Appendix C - Oak Island Geophysical Survey

APPENDIX C

OAK ISLAND GEOPHYSICAL SURVEY

Oak Island Geophysical Survey: Phase 2

Descriptive Report

June 2019

Submitted to:

Submitted by:

310 A Greenfield Drive
Newport, NC 28570
252-247-5785
www.GeodynamicsGroup.com

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TABLE OF CONTENTS
1.0 INTRODUCTION ................................................................................................... 6
1.1 Background.................................................................................................................. 6
1.2 Survey Area ................................................................................................................. 6
1.3 Survey Objectives ........................................................................................................ 7
1.4 Data Deliverables Format and GIS Database .............................................................. 7
1.5 Report Purpose ............................................................................................................ 8
2.0 SURVEY LOGISTICS ........................................................................................... 8
2.1 Mobilization .................................................................................................................. 8
2.1.1 Survey Vessel ....................................................................................................... 8
2.2 Survey Equipment........................................................................................................ 9
2.3 Survey Schedule .........................................................................................................11
2.4 Personnel ...................................................................................................................11
2.5 Weather ......................................................................................................................11
3.0 METHODOLOGY ................................................................................................ 14
3.1 Navigation and Position ..............................................................................................14
3.1.1 Applanix POS MV ................................................................................................14
3.1.2 Horizontal Control ................................................................................................15
3.1.3 Vertical Control ....................................................................................................15
3.1.4 Towed Sensor Positioning ...................................................................................15
3.2 Multibeam Survey .......................................................................................................17
3.2.1 Multibeam Data Acquisition ..................................................................................17
3.2.1.1 Data Acquisition Software .............................................................................17
3.2.1.2 Sensor Offsets, Orientation and Alignment ...................................................17
3.2.1.3 Multibeam Calibrations .................................................................................18
3.2.1.4 Attitude Correctors ........................................................................................19
3.2.1.5 Dynamic Draft Correctors .............................................................................19
3.2.1.6 Sound Speed Corrections .............................................................................19
3.2.1.7 Tide / Water Level Corrections ......................................................................21
3.2.2 Bathymetric Data Processing ...............................................................................22
3.2.2.1 Data Processing Software ............................................................................22
3.2.2.2 Processing Workflow ....................................................................................23
3.2.2.3 Post-Processed Attitude and Positioning ......................................................23
3.2.2.4 Vessel Configuration File ..............................................................................23
3.2.2.5 Raw Data ......................................................................................................23
3.2.2.6 Water Level Correction (Tides) .....................................................................24
3.2.2.7 TPU and CUBE Surface Generation .............................................................24
3.2.2.8 Surface / Line Filters .....................................................................................25
3.2.2.9 Sounding Review ..........................................................................................25
3.2.2.10 Refraction Editing .........................................................................................26
3.2.2.11 Finalized Surface ..........................................................................................26
3.2.2.12 Data Quality Review .....................................................................................26
3.2.3 Backscatter Data Processing ...............................................................................26
3.2.3.1 Data Processing Workflow ............................................................................27
3.2.3.2 Manual Editing ..............................................................................................28
3.2.3.3 Finalized Mosaic and Exporting to Backscatter Products ..............................29
3.3 Side Scan and Magnetometer Survey .........................................................................29
3.3.1 Side Scan and Magnetometer Survey Software ...................................................29
3.3.2 Side Scan Sonar ..................................................................................................30
3.3.2.1 Side Scan Workflow ......................................................................................30
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3.3.2.2 Data Acquisition ............................................................................................31
3.3.2.3 Data Processing ...........................................................................................32
3.3.3 Marine Magnetometer ..........................................................................................34
3.3.3.1 Magnetometer Workflow ...............................................................................34
3.3.3.2 Magnetometer Data Acquisition ....................................................................35
3.3.3.3 Magnetometer Data Processing ....................................................................35
3.4 Sub-bottom Survey .....................................................................................................36
3.4.1 Sub-bottom Workflow ...........................................................................................36
3.4.2 Sub-bottom Survey Software ...............................................................................37
3.4.3 Sub-bottom Data Acquisition ................................................................................37
3.4.4 Sub-bottom Data Processing & Interpretation ......................................................39
3.4.5 Final Data Export and GIS Products ....................................................................40
4.0 SURVEY RESULTS AND DISCUSSION ............................................................ 41
4.1 Side Scan Sonar (Jay Bird) .........................................................................................42
4.2 Magnetometer (Jay Bird).............................................................................................44
4.3 Multibeam (Jay Bird & Central Reach) ........................................................................47
4.4 Sub-bottom Sonar .......................................................................................................52
4.4.1 Data Results ........................................................................................................52
4.4.1.1 Jay Bird SBP Description ..............................................................................55
4.4.1.2 Central Reach SBP Description ....................................................................57
4.4.2 Data Products ......................................................................................................60
5.0 SUMMARY .......................................................................................................... 62
APPENDIX A: Project Scope of Work ........................................................................ 63
APPENDIX B: Calibration Documents ....................................................................... 73
APPENDIX C: Multibeam QA/QC Documentation ..................................................... 77

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LIST OF FIGURES

Figure 1. Survey map illustrating the bounding areas (in black) of the Central Site offshore of Oak
Island, NC. Proposed MBES survey lines are displayed in red. ................................................. 6
Figure 2. Survey map illustrating the bounding areas (in black) of the Jay Bird site offshore of Oak
Island, NC. Proposed SBP survey lines (with concurrent MBES) are displayed in red. ............. 7
Figure 3. R/V 4-Points. .............................................................................................................. 8
Figure 4. Tidal and meteorological conditions from Leg 1. ........................................................12
Figure 5. Tidal and meteorological conditions from Leg 2. ........................................................13
Figure 6. Fort Fisher CORS station is the nearest station that was used to transmit RTK Global
Navigation Satellite System (GNSS) corrections to the survey vessel. The VRS network utilized
a solution derived from several nearby base stations. ...............................................................14
Figure 7. POS MV system used for navigation and attitude corrections. ..................................15
Figure 8. Towing winch and cable counter aboard the R/V 4-Points used for deploying, acquisition
and retrieving the magnetometer and side scan sonar towing configuration. .............................16
Figure 9. Side scan sonar (left) and magnetometer (right) survey configuration. Figure extracted
from Edgetech’s “4200 Magnetometer Interface” addendum. ....................................................16
Figure 10. Map showing patch test data for the R/V 4-Points in the Morehead City Port. The
NOAA chart 11547-1 is displayed in the background. ...............................................................18
Figure 11. AML Micro SV used for real-time sound speed corrections. The probe is located on
the R/V 4-Points sonar mount near the transducers. .................................................................19
Figure 12. AML Smart SV&P used for sound speed profiles. ...................................................20
Figure 13. Sound speed profiles taken throughout the Jay Bird full coverage MBES survey (~3
days). The graph doesn’t include casts taking on survey days collected specifically for SBP
vertical alignment. .....................................................................................................................20
Figure 14. Sound speed profiles taken throughout the Central Reach full coverage MBES survey
(~2 days). The graph doesn’t include casts taking on survey days collected specifically for SBP
vertical alignment. .....................................................................................................................21
Figure 15. Graphic showing the major steps in bathymetric data processing. ..........................23
Figure 16. Subset view showing a cross-section of multiple days of data that used an SBET for
processing the ERS tidal corrections. The different colors of the soundings represent separate
line files. The data agrees vertically throughout the cross-section through several days of data
collection. The data has a 30x vertically exaggeration. .............................................................24
Figure 17. Screen capture showing multiple lines loaded in the Subset Editor. The yellow slice
bar inside the red oval, seen in the top plan view, is represented by the 2D subset view in the
lower left, while the 3D view, in the lower right window, shows the entire subset view box (entire
yellow outlined box within the red oval). ....................................................................................25
Figure 18. Screen capture showing one line of sonar data opened in CARIS’s Swath Editor. The
Swath Editor shows a slice of the data, colored by port and starboard beams, looking from the
rear direction. The section viewed is displayed in the top plan view. .........................................26
Figure 19. Workflow diagram showing the major steps in backscatter processing for this project.
.................................................................................................................................................28
Figure 20. Image illustratrating the “cut segment” tool in FMGT. ..............................................28
Figure 21. Side Scan Sonar Workflow .......................................................................................30
Figure 22. Example of Geodynamics’ Edgetech 4200 HFL side scan sonar towfish, as it was used
during the survey. .....................................................................................................................31
Figure 23. Example of real-time waterfall view in Discover monitored for SSS data quality. .....32
Figure 24. Image displays example of raw side scan sonar data (left) and the effect of applying
the EGN filter (right). .................................................................................................................33
Figure 25. Marine Magnetometer Workflow ...............................................................................34
Figure 26. SeaSPY 2 Overhauser magnetometer. ....................................................................35
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Figure 27. Sub-bottom workflow ................................................................................................36
Figure 28. Photo showing the surface tow of the SB-512. ........................................................38
Figure 29. Screen capture showing typical sub-bottom sonar data acquisition in Discover.......39
Figure 30. Illustration of towfish geometry relative to the sea surface, showing the seafloor and
multiple ray paths. .....................................................................................................................40
Figure 31. Location maps of scan sonar targets across the Jay Bird Shoals survey area. .........43
Figure 32. Magnetic anomalies identified and provided by Tidewater Atlantic Research, Inc. ..45
Figure 33. Distribution of magnetic anomalies as seen from the gridded normalized gamma
dataset, with a digitization of the observed linear anomaly. .......................................................46
Figure 34. Bathymetric surface for Jay Bird. The surface is overlaid with 1 ft contours and is at
a 5 ft spatial resolution. .............................................................................................................48
Figure 35. Backscatter mosaic for Jay Bird. The mosaic is at a 5 ft spatial resolution. ............49
Figure 36. Bathymetric surface for Central Reach. The surface is overlaid with 1 ft contours and
is at a 5 ft spatial resolution. ......................................................................................................50
Figure 37. Backscatter mosaic for Central Reach. The mosaic is at a 5 ft spatial resolution. ...51
Figure 38. Color scheme used for core units at both Jay Bird and Central sites. ......................52
Figure 39. Sub-bottom profile navigation tracklines, with line and file names, start points, and
arrow indicators for line direction for Jay Bird. ...........................................................................53
Figure 40. Sub-bottom profile data navigation tracklines, with line and file names, start points,
and arrow indicators for line direction for the Central area. .......................................................54
Figure 41. The shallow, surface bounding horizon (blue) at the Jay Bird Shoal site. The faint
dashed green lines denote 10 ft depth intervals. .......................................................................55
Figure 42. 3D image of showing the bathymetry overlaid on the profiles, showing the horizons
thin in deeper waters (blue) away from the shoal. .....................................................................56
Figure 43. The base reflector (light blue) in the E portion of the Jay Bird Shoals area. .............56
Figure 44. 3D view of the NE corner of the Central area displaying some of the characterizing
nature of the two depictable horizons. .......................................................................................57
Figure 45. The eastern box of the Central survey area, showing the extents of the “shallow”
reflector (dark orange) in the NE corner over the shallowest portion of the survey area. Below,
the “base” reflector (lime green) marks the deepest, continuous reflector. ................................58
Figure 46. 3D view of the northern end of the survey area, focused on the area between the two
boxes to show the paleo channel feature (tip of North arrow) that underlies the bathymetric
escarpment that extends from the western end of the eastern box (Box 2). ..............................59
Figure 47. 3D view of the Central area, showing the base reflector shoaling towards the surface
in the western part of the survey area with minimal acoustic penetration below the reflector. ....59
Figure 48. Isopach grid and contours developed from reflectors digitized in sub-bottom profile
imagery. ....................................................................................................................................60
Figure 49. View of the ArcGIS platform with the embedded profiles accessible as attachments by
clicking the trackline with the “i” tool. .........................................................................................61
Figure 50. Hyperlinked PDF of sub-bottom profile imagery, with start and end of lines marked
along with the cardinal direction of that start/end point. .............................................................61
Figure 51. 3D interactive web page, allowing pan, tilt, zoom and vertical exaggeration. ...........62
Figure 52. Cross-line to main scheme surface comparison at Jay Bird. Since the cross-line only
surface is not a deliverable and cross-lines are not included in the final bathymetric surface, fliers
may exist in this surface. Therefore, the large min/max values can be attributed to these fliers/the
lack of data for CUBE generation in the cross-line only surface. The mean (0.00 m) and standard
deviation (0.06 m) are the more meaningful results. Note the statistics are in meters. .............78
Figure 53. Cross-line to main scheme surface comparison at Central Reach. Since the cross-line
only surfaces are not a deliverable and cross-lines are not included in the final bathymetric
surface, fliers may exist in this surface. Therefore, the large min/max values can be attributed to
these fliers/the lack of data for CUBE generation in the cross-line only surfaces. The mean (0.00
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m, 0.03 m) and standard deviation (0.06 m, 0.04 m) are the more meaningful results. Note the
statistics are in meters. .............................................................................................................79
Figure 54. The yellow slice within the red box (top view) is illustrating the data displayed in the 2D
subset view (bottom image). In the 2D subset view, the tan soundings represent the cross-line,
while all other main scheme lines are displayed in various colors. The data is exaggerated to 20X
and shows good agreement. .....................................................................................................80
Figure 55. The yellow slice within the red box (top image) is illustrating the data displayed in the
2D subset view (bottom image). In the 2D subset view, the light blue soundings represent the
cross-line. The data is exaggerated to 20X and shows good agreement ..................................81
Figure 56. Displaying the difference surface derived from differencing 2015 R/V Benthos
multibeam data from the 2019 R/V 4 Points data. The graph displayed in the upper left potion of
the figure shows the statistics generated from this differencing. Overall, the data shows
agreement between datasets. ...................................................................................................82
Figure 57. NOAA chart comparison in the Central Reach. The 2019 data was transformed to
MLLW (using NOAA Vdatum) for this comparison. In CARIS, the mouse is hovered over the
charted sounding and the white information bar displays the value attributed to the bathymetric
surface. Overall, the datasets show agreement. .......................................................................83

LIST OF TABLES

Table 1. General Vessel Specifications of the R/V 4-Points. ..................................................... 9
Table 2. Table listing all survey equipment utilized for the project. ...........................................10
Table 3. Survey activities throughout Phase 2 data acquisition. ...............................................11
Table 3. A list of all survey personnel and management staff for this project. ...........................11
Table 4. Processing software utilized throughout the survey for multibeam sonar data. ...........22
Table 5. Table listing software used in backscatter data processing. .......................................27
Table 6. Software used by Geodynamics in geophysical data acquisition and processing. ......29
Table 7. Software used in geophysical data processing. ..........................................................37
Table 8. Attribute table generated for point shapefiles showing extents of digitized reflectors. .41
Table 9. Attribute table generated for the navigation tracklines shapefiles. ..............................41

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1.1 Background
Geodynamics was contracted by Moffatt and Nichol to perform a series of reconnaissance
surveys in support of future re-nourishment efforts on Oak Island, North Carolina (NC). This
report is in reference to Phase 2 of the project, which includes a combination of multibeam sonar
(MBES), side scan sonar (SSS), marine magnetometer (MAG), and sub-bottom profiling (SBP) at
two potential borrow sites offshore of NC.

The SSS and MAG data were acquired for object detection, identification of hard bottom areas,
and general characterization of the seafloor. The SBP data was acquired to determine the shallow
sediment distribution, identify subsurface features, and for geologic interpretations. The MBES
data was acquired to determine accurate depths at potential borrow areas and aid in SBP data
processing (vertically align the seafloor surface of the SBP to the bathymetry).

The overall survey scheme for the Jay Bird borrow area required full coverage MBES and SSS,
<100 ft spaced MAG lines, and SBP at a 1000 ft line spacing, forming a grid pattern (with
concurrent MBES). For the Central Reach borrow area, the overall survey scheme required full
coverage MBES and SBP at a 1000 ft line spacing forming a grid pattern (with concurrent MBES).
The Central Site only required SBP and MBES because the site was previously surveyed with
SSS and MAG in Phase 1 of the project.
1.2 Survey Area
The two potential borrow sites are approximately 1-3 nmi offshore of Oak Island, NC (Figure 1-
2). Sites include Central Reach (2 inset areas) and Jay Bird, as specified in the Scope of Work
(SOW) located in Appendix A.

Figure 1. Survey map illustrating the bounding areas (in black) of the Central Site offshore of Oak
Island, NC. Proposed MBES survey lines are displayed in red.
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Figure 2. Survey map illustrating the bounding areas (in black) of the Jay Bird site offshore of Oak
Island, NC. Proposed SBP survey lines (with concurrent MBES) are displayed in red.
1.3 Survey Objectives
The specific goals of this survey were to create the following deliverables:
• MBES:
o GIS Raster Dataset and Grid XYZ of bathymetric surface
o GIS Feature Class of elevation contours
• Magnetometer:
o GIS Feature Class and ASCII of Mag Anomalies with applicable descriptions
o GIS Raster Dataset of MAG Anomaly Surface
o GIS Feature Class of MAG Anomaly Contours
• Side scan:
o GIS Feature Class of SSS Targets with descriptions, linked to SSS target PDF
sheets
o GIS Raster Dataset of SSS Mosaic
• Sub-bottom Profiler:
o GIS Feature Class of SBP lines (Polyline) and in a PDF form with contacts and a
navigation map
o GIS Feature Class of SBP start and end points
o GIS Raster Dataset and Grid XYZ data of Isopach maps
• Cumulative Products (if applicable):
o GIS Feature Class of Points, Polygons, and Lines of interest
1.4 Data Deliverables Format and GIS Database
The data deliverables will be supplied on an external hard drive and when applicable, in a GIS
Database for overall usability and analysis of the final datasets. For a complete list of deliverables
refer to the ReadMe document on the deliverable drive.
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1.5 Report Purpose
The purpose of this document is to summarize the survey activities, report on the acquisition and
processing methodology of the data collected, and present the findings in regards to the SOW.
Magnetic anomalies were picked and reported on by Tidewater Atlantic Research, Inc for the Jay
Bird site; refer to this separate report within the final deliverable package for more information.

2.1 Mobilization

The Research Vessel (R/V) 4-Points (Figure 3, Table 1), owned and operated by Geodynamics,
was selected to support the MAG, SSS, MBES, and SBP survey of the borrow sites offshore of
Oak Island, NC. The R/V 4-Points was initially mobilized at Geodynamics’ headquarters in
Newport, NC and again on-site in Oak Island for a complete integration of the combined sensors.

Figure 3. R/V 4-Points.

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Table 1. General Vessel Specifications of the R/V 4-Points.
General Vessel Specifications
Vessel name R/V 4-Points
Owner Geodynamics
Dimensions: 25' x 10' x 1.2’
USCG: Designated Research Vessel
Flag: U.S.
Registry: North Carolina
Reg No: NC 5443 WV
Tonnage: 4.5
Lab space: 2 Operator Stations
Lavatory: Full head
Max Speed: 30 knots
Min. Survey Speed: 2.5 knots
Propulsion: 2 x 140HP Suzuki Outboard Motor -2011
Auxiliary Power: 5kW Fischer Panda Generator
Fuel Cap.: 120 gallons
GPS: Lowrance HDS-10
Magnetic Compass: Richie
Radar: Lowrance Broadband
Autopilot: Simrad AP-28
VHF: ICOM 504
Internet: Verizon 4G LTE JetPack
2.2 Survey Equipment
Table 2 lists the survey equipment used for this project.

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Table 2. Table listing all survey equipment utilized for the project.
Hardware Equipment Function Manufacturer Model
Na
v
i
g
a
t
i
o
n

&

A
t
t
i
t
u
d
e

Primary GNSS Receiver -
Positioning and
Orientation System for
Marine Vessels (POS MV)
Position/Attitude/Heading Applanix 320 v5
Primary GNSS Antenna
(port) Position/Attitude/Heading Trimble/
Aeroantenna Zephyr II
Secondary GPS-GNSS
Antenna (starboard) Position/Attitude/Heading Trimble/
Aeroantenna Zephyr II
Inertial Motion Unit (IMU) Position/Attitude/Heading Applanix IMU-38
2 GPS Cables (20 m) Position/Attitude/Heading Trimble n/a
IMU Cable (30 m) Position/Attitude/Heading Applanix IP68
Cellular Internet Mobile Internet Verizon Jetpack
Trimble SPS 461 Position (DGPS) Trimble 461
Cable Counter (SSS &
MAG) Layback Position CMAX CM2
SS
S

SSS (300-600 kHz) Object Detection Edgetech 4200 HFL
Operator station Acquisition Edgetech n/a
SSS deck cables (30m) SSS Telemetry Edgetech n/a
Ma
g
n
e
t
o
m
e
t
e
r
Magnetometer Anomaly Detection SeaSPY2 M-SM1000-
P03
Isolation Transceiver 48V Diagnostic Tool SeaSPY2 MS-SS3003
Tow cable Mag. Telemetry SeaSPY2 TC1000
Test cable SSS Integration Test
Cable SeaSPY2 M-SS2210
Test cable SSS Integration Cable SeaSPY2 TCSSS-S
MB
E
S

Sonar Processing Unit
(PU) Bathymetry Kongsberg 2040C PU
2 15m Sonar Cables Bathymetry Kongsberg EM2040
Surface Sound
Velocimeter Bathymetry Applied
Microsystems
Micro Sound
Velocity (SV)
Sound Profile Velocimeter Bathymetry Applied
Microsystems Smart SVP
2 Sonar Heads Bathymetry Kongsberg 2040C-Dual
Head
Su
b
-bo
t
t
o
m
SBP (0.5-12 kHz) Imagery/Geology Edgetech SB-512i
Poly-balls SBP Surface Towing n/a n/a
Operator station Acquisition Edgetech n/a
SBS deck cables (30m) SSS/SBS Telemetry Edgetech n/a
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2.3 Survey Schedule
Survey activities were conducted from June 16 – June 29, 2019, in two separate legs, totaling a
period of 10 days. Table 3 shows a generalized timeline of mobilization, acquisition and
demobilization activities.

Table 3. Survey activities throughout Phase 2 data acquisition.
Date Julian
Day Description of Survey Operations
6/13/19 164
Prep vessel and transit with trailered vessel to Southport Marina in
Southport, NC. Launch vessel, dry test of equipment, and dock vessel in
slip.
6/14/19 165 SSS, MAG, and MBES collection at Jay Bird. All three systems were run
simultaneously.
6/15/19 166 Continue SSS, MAG, and MBES survey of Jay Bird.
6/16/19 167
Continue SSS, MAG, and MBES survey of Jay Bird. Completed shallow
portion of the survey area during high tide. Completed all MBES
recoveries. All SSS, MAG, and MBES in Jay Bird was completed.
6/17/19 168 Transit back to Morehead City with vessel.
6/25/19 176
Transit with vessel down to Southport. Launch vessel, utilize boat lift at the
marina to get SBP in the water, and tie-off SBP to vessel. Take vessel to
slip and test computers and equipment.
6/26/19 177 SBP of Jay Bird. MBES was run simultaneously. Shallow sections were
run during high tide. SBP of Jay Bird was completed.
6/27/19 178
SBP of Central Reach site. MBES was run simultaneously. All SBP
collection in the Central Reach site was completed. Only MBES remaining
at that site.
6/28/19 179 Continue MBES in the Central Reach site.
6/29/19 180 Finish MBES in the Central Reach site. Use boat lift at marina to get SBP
out of the water. Trailer vessel and head back to Morehead City.
2.4 Personnel
See Table 3 for a list of all survey personnel and management staff involved in this project.
Table 4. A list of all survey personnel and management staff for this project.
Participant Title Affiliation
Chris Freeman President, Project Administrator Geodynamics
Dave Bernstein Chief Hydrographer, Project Manager Geodynamics
Ben Sumners Vessel Captain, Surveyor, Principal
Investigator Geodynamics
Nick Damm Surveyor Geodynamics
Davis Batten Surveyor Geodynamics
2.5 Weather
Meteorological observations from the nearby tide station at Wrightsville Beach, NC for each day
of survey (Figure 4-5).
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Figure 4. Tidal and meteorological conditions from Leg 1.
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Figure 5. Tidal and meteorological conditions from Leg 2.
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3.1 Navigation and Position
Each data point obtained during the survey activity had a geographic location associated with it
to facilitate database entry and display of these data within a Geographical Information System
(GIS) framework. To obtain more accurate real-time corrections, position and elevation data were
provided through a Virtual Reference Station (VRS) network, with Real-Time Kinematic (RTK)
corrections received via an internet connection. The VRS network derives a solution from
numerous nearby base stations, the nearest being the CORS station at Fort Fisher (Figure 6).

Figure 6. Fort Fisher CORS station is the nearest station that was used to transmit RTK Global
Navigation Satellite System (GNSS) corrections to the survey vessel. The VRS network utilized a
solution derived from several nearby base stations.

The Applanix Positioning and Orientation System for Marine Vessels (POS MV) 320 V5 Global
Positioning and Inertial Reference System was installed on the R/V 4-Points prior to mobilization
(Figure 7). The system was primarily used to monitor and integrate vessel attitude with horizontal
positioning information obtained from the dual-antenna spread, which supports Global Navigation
Satellite System (GNSS) satellites, and then provides navigation to HYPACK. This system
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provides real-time roll and pitch accuracy Root-Mean-Square (RMS) to 0.02°, heading to 0.02°
(with a 2 m antenna baseline), heave accuracy to 5 cm or 5% (whichever is greater), and
positional accuracy to ±1.0 m using standard Differential GPS (DGPS) receivers.

Figure 7. POS MV system used for navigation and attitude corrections.

Data were acquired in North American Datum of 1983 (NAD83) 2011 North Carolina State Plane
coordinate system with U.S. Survey Feet units. The horizontal control was provided by the POS
MV system and was corrected using DGPS/GNSS technology. In the event the real-time network
corrections service was to go out, the navigation system was setup to receive the differential
corrections from a nearby DGPS station using an auxiliary DGPS antenna.

The post-processed vertical datum for bathymetric data is NAVD88 (Geoid12b). Survey data was
collected using vertical corrections from the VRS real-time network. These corrections provided
the necessary information for the ellipsoid heights to be post-processed to NAVD88 by integrating
GPS Tides and the geoid model. Multibeam bathymetry data was ultimately controlled vertically
by post-processing the logged navigation and attitude file (*.000) in POSPac and integrating the
smoothed best estimated trajectory (SBET) back into the bathymetric data in CARIS (Section
3.2.2.3).

The MAG and SSS were towed from the center, stern of the vessel and were separated by a 30-
ft tether (Figure 8-9). A towing winch was used to deploy and retrieve both devices, while an
attached cable counter accurately measured cable out length. Cable out length was entered and
monitored in HYPACK navigation software to determine, and apply, magnetometer and SSS
layback. Reciprocal survey lines were run for post-processing verification of accurate layback
corrections, as well as review of intersections during post-processing.

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Figure 8. Towing winch and cable counter aboard the R/V 4-Points used for deploying, acquisition
and retrieving the magnetometer and side scan sonar towing configuration.

Figure 9. Side scan sonar (left) and magnetometer (right) survey configuration. Figure extracted
from Edgetech’s “4200 Magnetometer Interface” addendum.
The SBP towfish was deployed with a set of poly-balls attached to the towpoint. This maximized
the distance between the towfish and the seafloor, therefore, the depth of the reflector. For more
information see Section 3.4.

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Figure 10. The SBP towed behind the R/V 4Points, using the surface-tow poly-balls.
3.2 Multibeam Survey

3.2.1.1 Data Acquisition Software
The HYPACK software suite was used during survey preparation in order to create survey line
plans and evaluate the overall survey scheme. HYPACK was also used during the survey in
order to record navigation, as well as to modify line plans on the fly (OTF) as necessary, log
targets of importance and provide the captain with line tracking.

Seafloor Information System (SIS) by Kongsberg was the data acquisition and user interface
software to accompany the EM2040C-D system. All multibeam data collected during the survey
were acquired using this software. SIS was also used for OTF identification of “holidays” or gaps
in the data and real-time quality assurance/quality control (QA/QC) of the multibeam sonar data.

The POSView software by Applanix was used with the POS MV system. The software provides
the platform to view and monitor the tightly-coupled integration of the attitude measurements
recorded by the IMU as well as the position, heading measurements, and accuracies recorded by
the GNSS antennas. POSView logged a POSPac file which contained all the attitude, positioning,
heading, and error estimate data. This file provides a QA measure to inspect the recorded
accuracies and/or post-process using Inertially-Aided Real Time Kinematic (IARTK) solutions.

Sound speed profiles (SSP) were acquired by the AML Smart SV&P velocimeter. The AML Smart
SV&P SSPs were processed in SeaCast, exported as Standard Code for Information Interchange
(ASCII) Sound Velocity Profiles (ASVP) files, and loaded directly into SIS to correct for sound
speed during data acquisition.
3.2.1.2 Sensor Offsets, Orientation and Alignment
The vessel offsets were measured during the initial system installation and mounting on the R/V
4-Points and checked during mobilization. Vessel offsets are entered in SIS and the POSMV to
ensure an accurate merging of IMU data with multibeam soundings.
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3.2.1.3 Multibeam Calibrations
Prior to survey, calibration of the GNSS Azimuth Measurement Subsystem (GAMS) system was
verified. The calibrations followed the auto-start procedure laid out in the POS MV V5 Installation
and Operation Guide. The GAMS parameters in the setup menu were initially set to zero, except
for the heading calibration threshold, which was set to 0.500°. The vessel then made aggressive
figure-8 maneuvers until the GAMS solution came online and the values in the parameter setup
menu were automatically updated.

The patch test for the R/V 4-Points was performed in April 2018 (systems have remained the
same). The patch test site was selected due to extensive prior survey operations performed by
Geodynamics, as well as for its numerous bottom features such as flat areas, submerged debris
and slopes (Figure 10). RTK-GNSS was utilized during the patch test and data were processed
on-site using the SIS patch utility and CARIS. The pitch, roll, and heading biases obtained for the
port and starboard transducers were entered in the Installation Parameters menu in SIS. Any
additional pitch, roll, and heading biases determined during post-processing were then entered in
the CARIS HVF. The latency between GNSS reception from the tightly-coupled POS MV and
integration by the acquisition system was also measured during the patch test. The patch test
followed the procedure laid out in the SIS EM2040C Reference Manual, How to calibrate a dual
head system. Complete details of the multibeam system calibration and results can be found in
Appendix B.

Figure 10. Map showing patch test data for the R/V 4-Points in the Morehead City Port. The
NOAA chart 11547-1 is displayed in the background.
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3.2.1.4 Attitude Correctors
Attitude or complex vessel motion corrections were provided by the POS MV. The Applanix POS
MV unit was setup to receive phase-differential position corrections through a VRS Network. This
configuration allowed the POS MV to integrate decimeter positional solutions with highly-accurate
vessel attitude measurements obtained from the IMU. When the GAMS was online, positional
solutions were being received from five or more satellite fixes with a Positional Dilution of
Precision (PDOP) equal to or less than three. Throughout the entire survey, POSView was
configured to log a file which contained all the attitude, positioning, heading, and error estimates
data (POSPac .000 file).
3.2.1.5 Dynamic Draft Correctors
Dynamic draft is the summation of the static draft, settlement, and squat corrections, and is a
required corrector for survey-grade echo soundings. Using VRS RTK-GNSS, the ellipsoid-based
vertical corrections received from the base station provided the survey vessel with an accurate
real-time elevation based on the vessels position in the water. This worked to factor out the static
draft, settlement, and squat of the survey vessel.
3.2.1.6 Sound Speed Corrections
Real-time surface sound speed was collected with an AML Oceanographic MicroSV (Figure 11).
The real-time surface sound speed information is used to correct for the refraction of sound in the
water to ensure accurate beam information throughout the survey.

Figure 11. AML Micro SV used for real-time sound speed corrections. The probe is located on the
R/V 4-Points sonar mount near the transducers.
The AML Smart SV&P velocimeter were used during the survey in order to obtain accurate sound
speed profiles throughout the survey area (Figure 12). The device measures sound speed directly
using “time of flight” technology, automatically compensating for pressure, salinity, and
temperature.

The sound speed profiles are downloaded via serial cable, where the survey technician then logs
the sound speed profile data and coordinates of the cast once the probe is recovered. The sound
speed profile is then imported directly into SIS for real-time corrections.

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Figure 12. AML Smart SV&P used for sound speed profiles.
The real-time sound speed at the transducers was automatically compared to the respective
depth and sound speed from the sound speed profile being used at any given time. To ensure
accuracy, Geodynamics has both sensors calibrated annually to minimize the effect of small
deviations in surface sound speed to beam forming accuracy. When the two sound speeds
deviated by approximately 2 meters per second (m/s), a warning would alarm the survey
technician of the potential for changing oceanographic conditions. Excluding multibeam collection
specific for SBP vertical alignment, a total of 14 sound speed profiles were taken during the full
coverage multibeam survey at Jay Bird and 5 sound speed profiles at Central Reach (Figure 13-
14).

Figure 13. Sound speed profiles taken throughout the Jay Bird full coverage MBES survey (~3
days). The graph doesn’t include casts taking on survey days collected specifically for SBP
vertical alignment.
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Figure 14. Sound speed profiles taken throughout the Central Reach full coverage MBES survey
(~2 days). The graph doesn’t include casts taking on survey days collected specifically for SBP
vertical alignment.
While routine sound speed profiles were taken whenever changes were observed in the surface
water, interactions with the bathymetry as well as upwelling, inlet/waterway flow, and thermal
exchange can introduce variations in sound speed profiles during the survey. For the duration of
this survey the sound velocity was rather consistent, however, a strong tide-line did have some
effect on sound speed corrections in Jay Bird. All pre-cautions in the field and office were taken
to accurately account for such change (additional casts, beam clips, SV correct in CARIS, etc.).
3.2.1.7 Tide / Water Level Corrections
Precision bathymetric survey data require accurate water level corrections in order to reference
the millions of individual depth measurements, or “pings”, to a common vertical datum of NAVD88.
Astronomic tides typically have the most significant effect on water level over a given area of
seafloor and are commonly accommodated for by using predicted tide zonation models.
However, meteorology and localized phenomena and features (i.e., salinity or temperature fronts)
can also have a measurable impact on water level at any given time. Tide zonation models
forecast water levels at a given date and time based upon astronomic tidal harmonics, but cannot
account for the short-term modification of tidal behavior due to inlet-based tidal effects, the effects
of barometric pressure, winds, seawater density and nearby currents (i.e., Gulf Stream intrusion),
distance from gauge, etc.

Therefore, to minimize Total Propagated Uncertainty (TPU) in the bathymetric survey data,
observed water level measurements were obtained throughout all hydrographic survey
operations. RTK-based water level measurements, relative to the ellipsoid, were continuously
recorded throughout the survey by the POS MV (POSPac .000 file). The GPS height determined
by the POS MV was integrated into the raw multibeam sonar data file in SIS. After converting the
raw data in CARIS, the GPS tide was computed, and the ellipsoid-based tidal measurements
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were then reduced to NAVD88 by integrating a local Geoid 2012b model. The GPS Tide is
computed in CARIS such to provide accurate tidal corrections and as a supplement to the IMU
for removing heave.

GPS Tide = GPS Height – Datum Height + Antenna Offset – Heave + Dynamic Draft – Waterline

The following sections discuss the steps taken in processing the multibeam bathymetry data
acquired with the EM2040C-D sonar. All bathymetric survey data were processed using CARIS
Hydrographic Information Processing Systems (HIPS) and Sonar Information Processing System
(SIPS) software and gridded in a Combined Uncertainty and Bathymetry Estimator (CUBE)
surface for each site at a final resolution of 5 ft. A surface resolution of 5 ft was chosen for the
final bathymetric data products based on data density and quality.
3.2.2.1 Data Processing Software
All multibeam bathymetric data processing software is listed in Table 4. Multibeam bathymetry
data were processed in CARIS HIPS and SIPS 11.1.0. This software provides a comprehensive
package to integrate time-tagged position, attitude, water level and sensor information into
sounding data to calculate an accurate CUBE surface. CARIS HIPS and SIPS also provided the
platform to clean and review sounding information, as well as assess TPU of individual soundings
and resulting surfaces.

Post-processing and inspection of position, attitude and navigation data as well as vessel and
sensor alignment and other QA measures were performed using the Applanix software, POSPac
Mobile Mapping Solutions (MMS) 8.3. The “In-Fusion Smart Base” method was utilized to post-
process navigation.

ArcGIS 10.5 software was used to project georeferenced datasets and various computational
surfaces, including maps and charts delivered for this project.
Table 5. Processing software utilized throughout the survey for multibeam sonar data.
Software Function Version Manufacturer
CARIS HIPS &
SIPS Bathymetry Processing 11.1.0 CARIS
POSPac Navigation/Attitude ]
Post-Processing 8.3 Applanix
Sound Speed
Manager SVP Comparison Graphs 2019.1.2 HydrOffice
ArcGIS Generating Final GIS Products 10.5 ESRI
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3.2.2.2 Processing Workflow

Figure 15. Graphic showing the major steps in bathymetric data processing.
3.2.2.3 Post-Processed Attitude and Positioning
POSPac MMS is a user-friendly suite of tools used to create an accurate solution of position,
orientation and dynamics from the GNSS and IMU data collected with the POS MV. Raw POS
data collected in the field is imported into POSPac MMS and an SBET is created using various
methods of post-processing. The post-processed SBET is then integrated into the multibeam
sonar data to enhance horizontal and vertical accuracy and the reliability of the GNSS data.
3.2.2.4 Vessel Configuration File
The CARIS vessel configuration file, called the HIPS Vessel File, is an Extensible Mark-up
Language (XML) file that can describe details of the installation and calibration of the instruments
installed and their precise positioning relative to each other and the vessel’s reference frame.
Embedded information within the HVF is used by multiple processes in CARIS to merge sensors,
offsets and calculate sounding uncertainty. For this project, measured sensor offsets and
calculated patch test offsets were applied to SIS or POSView prior to acquisition. Therefore, the
“apply” option for most offset values in the HVF, except for a few correctors applied in post-
processing, were set to “no”. However, sensor offsets are still placed in the HVF as well as other
manufacturer specifications to properly account for TPU.
3.2.2.5 Raw Data
The raw multibeam bathymetry data collected in SIS provides rough estimates of water depth and
morphology. In order to view the raw data and water levels as it was collected, a zero-tide must
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be applied which neglects all tidal influences on depths. Corrections applied to the raw data in
real-time included sound speed corrections from the most recent and appropriate sound speed
cast, as well as initial heave, pitch, roll, and heading corrections from the POS MV. However, raw
data may still include possible errors, including unaccounted for water level corrections, sonar
orientation biases, and errors in sound speed.
3.2.2.6 Water Level Correction (Tides)
Tidal observation data must be loaded for every track line before the soundings can be viewed
as depths and positions, correcting for astronomical and meteorological changes in water levels.
As this project is an Ellipsoidally Referenced Survey (ERS), real-time tidal and water level
changes were corrected by computing “GPS Tides” in CARIS. This procedure uses the GNSS
height and vessel heave to dynamically deduct the vessel’s vertical displacement through the
water column as well as correct for the astronomical changes in water level heights over the
course of the survey. Furthermore, with the addition of post-processed SBETs, the quality of the
GNSS heights is increased, thus producing a more reliable tidal correction (Figure 16).

Figure 16. Subset view showing a cross-section of multiple days of data that used an SBET for
processing the ERS tidal corrections. The different colors of the soundings represent separate
line files. The data agrees vertically throughout the cross-section through several days of data
collection. The data has a 30x vertically exaggeration.
3.2.2.7 TPU and CUBE Surface Generation
A CUBE surface is a surface which uses multiple hypotheses to represent potential depth
variances along the seafloor based on a TPU that is calculated in CARIS. The CARIS TPU
module computes horizontal and vertical uncertainty values, requiring user-entered estimated
error values for the tide, sound speed measurements and published errors from equipment
specifications. TPU calculations are used in the CUBE algorithm to calculate a surface where
‘nodes’ or ‘tiles’ are assigned to soundings with the lowest vertical uncertainties and are internally
self-consistent.
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3.2.2.8 Surface / Line Filters
Upon initial QC inspections and reviews for targets or features on the seafloor, a combination of
swath and surface filters were executed in CARIS to reduce manual editing. The main filter
utilized was a swath filter to remove erroneous outer beams.
3.2.2.9 Sounding Review
One of the last steps of multibeam processing is to manually “clean” or remove erroneous data
inherent to all multibeam echosounders. This is commonly due to aeration, pelagics, multiples,
or outer swath artifacts. Soundings were edited using a combination of Subset Editor and Swath
Editor. Subset Editor was used as a means of reviewing the data and cleaning erroneous
soundings (Figure 17). Multiple overlapping lines are loaded into the Subset Editor, providing the
processor with a confidence check for detecting features, assessing systematic errors, and
flagging fliers. This technique provides the user flexibility to review the data in both 2-dimensional
(2D) and 3-dimensional (3D) views.

Figure 17. Screen capture showing multiple lines loaded in the Subset Editor. The yellow slice
bar inside the red oval, seen in the top plan view, is represented by the 2D subset view in the
lower left, while the 3D view, in the lower right window, shows the entire subset view box (entire
yellow outlined box within the red oval).
Swath Editor provided an initial editor to review and clean individual lines, providing a slice that
preserves both large and small-scale features in the swath and reveals true outliers (Figure 18).
The erroneous data were flagged as rejected as to not be included in the final surface. The
Swath Editor also provided a means for reviewing the navigation and attitude data for spikes or
gaps and adjusting refraction coefficients if warranted. Surfaces were constantly recomputed
and reviewed for remaining fliers and cleaned as necessary.

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Figure 18. Screen capture showing one line of sonar data opened in CARIS’s Swath Editor. The
Swath Editor shows a slice of the data, colored by port and starboard beams, looking from the
rear direction. The section viewed is displayed in the top plan view.
3.2.2.10 Refraction Editing
While sound speed casts were taken routinely and as needed to properly beam-form the swath
data, rapid and spatially variable changes in sound speed due to environmental conditions
(inlet/waterway inputs, wind events, etc.) led to some minor issues with sound speed corrections.
In order to adjust the data with refraction issues, the Refraction Editor in CARIS HIPS was utilized.
A visual inspection was completed on all track-line data in sub-sections to analyze and adjust the
refraction coefficients. The trademark errors caused by sound speed discrepancies are a
“smiling” or “frowning” of the overlapping bathymetric sounding swaths (higher or lower predicted
sound speeds). Rather than leaving the refraction issue in the data and reducing the overall
quality of the final product, this method of refraction editing in CARIS was selected because of
the predictable bathymetric relief of the seafloor and ample swath coverage by which to gauge
the proper refraction correction values to be applied to the data.
3.2.2.11 Finalized Surface
The final surfaces are 5 ft resolution and were chosen to maximize data quality and realistically
account for data density for a given depth.
3.2.2.12 Data Quality Review
For this project, 3 main methods of data quality assessment were performed: (1) comparison of
main scheme to cross-lines (2) a junction analysis with overlapping 2015 Geodynamics multibeam
data; and (3) a NOAA Chart comparison. Details about each of these methods and the results
of the assessment can be found in Appendix C.

The dual-head EM2040C-D collected backscatter intensity information when the multibeam was
operating. The following sections outline the information and steps included in processing the
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multibeam backscatter data. Although this was not a direct requirement, Geodynamics believed
this product would be useful in analysis.

Processing of the multibeam backscatter data was performed in the QPS software, Fledermaus
Geocoder Toolbox (FMGT) (Table 5). The software is designed to visualize and analyze
backscatter data from multibeam sonars, performing a series of corrections aimed to maximize
the information content within the backscatter signals. The software utilizes Geocoder, a software
tool that implements geometric and radiometric corrections of backscatter intensities from the
sonar and corrects for variable acquisition gains, power levels, pulse widths, ensonification areas
and incidence angles to provide high-resolution and more accurate geo-referenced images of
seafloor morphology and physical properties.

ArcGIS 10.5 software was used to project georeferenced datasets and various computational
surfaces, including maps and charts delivered for this project.
Table 6. Table listing software used in backscatter data processing.
3.2.3.1 Data Processing Workflow
The backscatter was processed into one FMGT project per site. The data was processed using
the Automatic Processing method in FMGT. This method first adjusts the backscatter data by
performing backscatter extraction and then applies radiometric corrections based on sonar type
and bottom topography. Next, it performs filter processing, which includes angle varying gain
(AVG) adjustments as well as anti-aliasing of the backscatter data. As this stage progresses, the
results of the backscatter adjustment are incorporated into the project hierarchy and a mosaic is
created.

For this project, the backscatter was processed into a “time series” mosaic. The mosaic resolution
was defined at a resolution appropriate for the depth and data density. Once the mosaic was
created, the processor manually edited the lines within the mosaic to clean out erroneous
areas/data. Following manual editing, the mosaics were exported for use in ArcGIS. The ArcGIS
grids contain a processed backscatter value in decibel (dB) for each pixel.

The overall workflow of backscatter processing in FMGT is shown below in Figure 19.

Software Function Version Manufacturer
FMGT Backscatter Processing 7.7.9 QPS
ArcGIS Generating Final GIS Products 10.5 ESRI
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Figure 19. Workflow diagram showing the major steps in backscatter processing for this project.
3.2.3.2 Manual Editing
Once the data was imported, specific lines were selected to create a mosaic and the processor
manually edited sections of the data that contained errors. The processor generally excluded
cross-lines, turns, and erroneous lines when creating the mosaic. However, when entire lines
could not be excluded, the processor used the “cut segment”, and “add segment” in FMGT to
manually edit the data. The cut segment allows the processor to exclude portions of the line that
have errors due to turns, aeration, noise in the water column, and other erroneous backscatter
situations (Figure 20).

Figure 20. Image illustratrating the “cut segment” tool in FMGT.
The “add segment” tool is the same concept, however, lets you add back in segments that may
have been deleted or excluded.

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3.2.3.3 Finalized Mosaic and Exporting to Backscatter Products
Following the manual editing of the mosaics, the mosaics were exported as ASCII grids. The
ASCII grid files were then converted to ArcGrids, clipped based on survey area extents and
appropriate resolution, and exported as final ArcGrids. The final backscatter mosaics were
created at 5 ft resolution to mimic the final bathymetric products.
3.3 Side Scan and Magnetometer Survey
The following section outlines the equipment, software, and methods of acquiring and processing
MAG and SSS data aboard the R/V 4-Points. Each section serves to illustrate critical steps for
collecting and processing of the geophysical data.

All geophysical data acquisition and processing software used by Geodynamics is detailed below
and listed in Table 6. The POS MV integrated RTK-GNSS corrections for the vessel throughout
all geophysical data acquisition. In the event RTK corrections were lost, the Trimble SPS 461
DGPS provided corrections for vessel positions within +/- 1 m.

The HYPACK software suite was used during the survey to manage and integrate navigation for
towed sensors and line tracking. In addition, HYPACK provided layback corrected SSS towfish
position through cable out measurements from a CMAX pulley, sending the final layback
corrected positions directly to the Discover acquisition software. Magnetometer data were
acquired through a separate HYPACK driver.

Discover 4200 Series 4.0 is a version of Edgetech’s native acquisition software specifically
designed for the acquisition of SSS with Edgetech systems. It provided a waterfall data display
for both the high and the low QA/QC. Discover logged all RAW data along with time and navigation
stamps in Edgetech’s proprietary JSF file format file for high and low frequency SSS data.

SSS data were processed and interpreted in SonarWiz 7 version 7.00.0008. Alongside the ability
to process, analyze, and interpret the SSS data, SonarWiz provides a platform to review and
process the navigation data and can then export deliverables for direct inclusion in GIS charts
and reports.

Magnetometer data were initially reviewed by Geodynamics, then sent to Tide Water Atlantic
Research to be processed and interpreted. HYPACK was the only software used by Geodynamics
for magnetometer acquisition and initial processing of the data into X, Y, Gamma edited files, as
well as layback adjustments.

ArcGIS software was used to assimilate data products and perform interpretations in one
comprehensive platform. Data products and maps were generated to be displayed in this GIS
platform.
Table 7. Software used by Geodynamics in geophysical data acquisition and processing.
Software Function Version Manufacturer
HYPACK
Navigation management, cable out and
navigation pass-through / Magnetometer
data acquisition
2018 HYPACK
Discover 4200 Side scan sonar interface and recording 4.00 Edgetech
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3.3.2.1 Side Scan Workflow

Figure 21. Side Scan Sonar Workflow
SonarWiz Side scan and Sub-bottom sonar processing
and interpretation V7.7.0008 Chesapeake
Technology
ArcGIS
Develop, mosaic and assimilate
targets/anomalies, comprehensive
interpretations
10.5 ESRI
Project Planning
•GIS Development
•Survey Design
•Client Revisions
•Final Survey Plan

Survey Control Logistics
•Confirm survey control
requirements and measure
offsets
•Check survey position
verification location
•Create detailed digital notes

Side Scan Setup
•Input Vessel Survey Offsets
•Perform Dry Rub Test
•Perform Wet Test, Range Test,
Resolution Test
•Assess Results and Quality

Survey Data Acquisition
•Log Data with Navigation in Discover
•Log Targets of Interest/Importance
•Maintain Towfish Altitude
•Complete Daily Survey Notes
•Backup All Data
Survey Data Processing
•Import data into SonarWiz
•Apply gains & filters
•Adjust layback (if needed)
•Review/repair navigation
•Log targets and features of
significance
•Export Data/Maps/Products
Final Reporting
•Create Final Report Document
•Assimilate Data, Notes, QA/QC
•Use Official SOW as Checklist
•Finalize Report and Data Products
•Produce final Data Product and
interpretations for delivery and
backups
QA-QC
•Check Vessel Survey #’s and
Software Input
•Verify Settings in line with SOW
•Documentation of System Setup
•Verify calculated position of
sensor with MBES positioning
QA-QC
•Navigation & SSS Altitude/ Health
Checks
•On-site calibration line for settings
•Data Quality and Data Coverage
Check, I.E. Range Test
•Overall Survey Coverage
Assessment
•Review processed data quality in
SonarWiz QA-QC
•Coverage/Density
Assessment
•NAV Quality
Assessment
•Line-to-Line Feature
Assessment
•Target agreement in
overlap

Mobilization
•Secure all gear/equipment and
backups for project
•Vessel/install equipment
•Perform/Confirm dimensional control
and document system integration
•Comms test
•Test Vessel Nav/GPS
•Load HYPACK Navigation Project

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3.3.2.2 Data Acquisition
Side scan sonar data were acquired with an Edgetech 4200 HFL dual frequency sonar (Figure
22). Navigation was provided by the POS MV with RTK-GNSS corrections via wireless internet
connection. The corrected position was sent from the POS MV into HYPACK and then given a
lever-arm offset to the tow point and cable out measurement from the cable counter. This towfish
navigation solution was interpreted by HYPACK Survey and then exported as a GGA string via a
RS-232 cable back to the Edgetech 4200 topside unit, where it was integrated and recorded in
Edgetech’s Discover software on the geophysical control computer. Data were recorded in JSF
format files (used in processing), containing both the 300 and 600 kHz frequencies. The range
setting for the towfish was set at 25 m (e.g. 50 m swath) for the entire survey. Survey speeds
were maintained around 3-4 knots (kt). Towfish altitude was monitored at the acquisition station
and adjusted via a winch remote, maintaining an altitude of ~ 10 – 20% of the SSS data range.
This maintained altitude correlated to around 3 – 4 m above the seabed, with the primary goal to
have the MAG below 6 m altitude.

Figure 22. Example of Geodynamics’ Edgetech 4200 HFL side scan sonar towfish, as it was used
during the survey.
Real-time acquisition data quality and coverage was constantly monitored in the Discover
waterfall view (Figure 23). Targets were logged and noted in the field as observed targets,
however, final targets and features presented in the results were documented and verified during
post-processing. Sonar swath range was constantly monitored for full range performance while
maintaining optimum altitude of the magnetometer and a line spacing ≤100 ft.
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Figure 23. Example of real-time waterfall view in Discover monitored for SSS data quality.
3.3.2.3 Data Processing
Individual SSS JSF files were imported into SonarWiz, which generates a corresponding
Chesapeake Tech Sonar Format (CSF) file. Navigation and heading from the layback driver to
the towfish was smoothed using “course made good” and an average of 300 pings was used to
smooth the navigation. Each SSS file was bottom tracked to remove water column data. The
Empirical Gain Normalization (EGN) filter (Figure 24) was then applied to all SSS lines to improve
and harmonize gains and appearance.

Side scan sonar targets were picked on individual SSS lines and confirmed on adjacent lines,
when available. Data were reviewed for areas/features of significance and evidence of potential
hardbottom. Areas that may suggest potential debris that could possibly interfere with dredging
and/or cultural resources were marked and included in a point shape file and target report with
final deliverables. Final products include target dimensional attributes and description, where
applicable.

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Figure 24. Image displays example of raw side scan sonar data (left) and the effect of applying the
EGN filter (right).
To generate the final SSS mosaic, data were exported into a 1-ft cell size, 8-bit, 4 band mosaic
TIFF, exported with higher values representing more reflective material.
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3.3.3.1 Magnetometer Workflow

Figure 25. Marine Magnetometer Workflow

Project Planning
•GIS Development
•Survey Design
•Client Revisions
•Final Survey Plan

Survey Control Logistics
•Confirm survey control
requirements
•Check survey position
verification location
•Create detailed digital
notes
Magnetometer Setup
•Input Vessel Survey Offsets
•Calibrate / Measure Tow Cable
•Configure MAG in HYPACK
•Perform Ferrous Dry Test
•Perform Wet Test
•Assess Results and Quality

Survey Data Acquisition
•Log HYPACK Navigation
•Log MAG Data
•Log Targets of Interest/Importance
•Complete Daily Survey Notes
•Backup All Data
Survey Data Processing
•Import MAG Data into HYPACK
Mag editor
•Process Navigation
•Correct & Normalize Data
•Select Anomalies (Tidewater)
•Export Targets (Tidewater) &
Line Data
•Produce GIS
Data/Maps/Products
Final Reporting
•Create Final Report Document
•Assimilate Data, Notes, QA/QC
•Use Official SOW as Checklist
•Finalize Report and Data
Products
•Produce final data products for
delivery and backups
QA-QC
•Check Vessel Survey
#’s and Software Input
•Verify navigation and
MAG data
•Documentation of
System Setup

QA-QC
•Navigation & MAG Altitude
Health Checks
•Data Quality and Data
Coverage Checks
•Overall Survey Coverage
Assessment
•Review/Assess Targets
QA-QC
•Coverage Assessment
•Line-to-Line Feature
Assessment
•Anomaly Location
Assessment

Mobilization
•Secure all gear / equipment
and backups for project
•Ship / bring / install equipment
•Perform dimensional control
and document system
integration
•Install and connect
magnetometer
•RS232 test / Ferrous Test
•Test Vessel GNSS

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3.3.3.2 Magnetometer Data Acquisition
A SeaSPY 2 Overhauser magnetometer was used to acquire magnetic anomaly data (Figure 26).
RTK-GNSS corrected positions were input into HYPACK (for layback position) to control
navigation and data collection during the MAG survey. To ensure proper altitude per archeological
recommendations, the SSS/MAG configuration was towed approximately 3-4 m above the seabed
and no more than 6 m above seabed.

MAG data were acquired in HYPACK after being passed through Discover. Corrected SSS
towfish navigation data was given an additional 35-ft offset, as to account for the MAG sensor
position behind the SSS. Data were recorded in HYPACK’s RAW file format, where the gamma
value is recorded as the Z value.

Figure 26. SeaSPY 2 Overhauser magnetometer.
3.3.3.3 Magnetometer Data Processing
Magnetometer data were sent to Tidewater Atlantic Research in Washington, NC to be processed
and interpreted.

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3.4 Sub-bottom Survey
The following section outlines the equipment, software and methods of acquiring and processing
geophysical sonar data aboard the R/V 4-Points. Each section serves to illustrate individual,
critical steps for collecting or processing of the geophysical data.

Figure 27. Sub-bottom workflow
Project Planning
•GIS Development
•Survey Design
•Client Revisions
•Final Survey Plan

Survey Control Logistics
•Confirm survey control
requirements
•Check survey position
verification location
•Create detailed digital notes

Chirp Setup
•Input Vessel Survey Offsets
•Perform Dry Ping Test
•Perform Wet Test, Chirp Sweep &
Power settings
•Assess Results and Quality

Survey Data Acquisition
•Log Data with Navigation (in
Discover)
•Log Targets of Interest/Importance
•Maintain Towfish Altitude and cable
out
•Complete Daily Survey Notes

Survey Data Processing
•Import data into SonarWiz
•Apply gains & filtering
•Apply datum correction
•Integrate cores
•Interpret horizons & targets
•Produce GIS
Data/Maps/Products
Final Reporting
•Create Final Report Document
•Assimilate Data, Notes, QA/QC
•Use Official SOW as checklist
•Finalize Report and Data
Products
•Produce final data product for
delivery and backups
QA-QC
•Check Vessel Survey
#’s and Software Input
•Verify Settings in line
with SOW
•Documentation of
System Setup
QA-QC
•Navigation & SBP Altitude Health
Checks
•On site calibration line for settings
•Data Quality and Data Coverage
Checks
•Overall Survey Coverage
Assessment
•Review/Assess Penetration and
Targets QA-QC
•Coverage/Density
Assessment
•Line-to-Line Feature
Assessment
•Sub-bottom
penetration
assessment

Mobilization
•Secure all gear/equipment and backups
for project
•Install equipment
•Perform dimensional control and
document system integration
•Connect hydro winch and connect
towfish
•Comms test
•Test Vessel GPS & corrections
•Load HYPACK Navigation Project

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All geophysical data processing software is detailed below and listed in Table 7. The geophysical
survey equipment was operating independent of the multibeam system. The POS MV provided
DGNSS navigation for all geophysical data.

The HYPACK software suite was used during the survey to manage navigation and line planning
as well as serve as an interface between the POS MV navigation output and the towfish to provide
manual layback corrected position and heading to the SBP controller software.

Discover SBP is a version of Edgetech’s native acquisition software specifically designed for the
acquisition of SBP for Edgetech systems. It provided a rolling data display of sub-bottom
penetration and resolution, allowing real-time QA/QC. Discover logged all RAW data along with
time and navigation stamps in Edgetech’s proprietary JSF file format, as well as XTF and SEGY
for posterity.

Sub-bottom Compressed High-Intensity Radiated Pulse (CHIRP) data were processed using
SonarWiz 7 version 7.00.0008 x64 software. The final processed data have been datum aligned
(snapped to the NAVD88 bathymetry) and processed with an envelope function and custom gain
settings to improve reflector continuity and interpretability. SonarWiz also provided the ability to
integrate available boring (core) data, digitize and interpret horizons, visualize continuity between
sub-bottom sonar line intersections and other datasets, export sediment thickness products, and
produce data reports.

Surfer software was used to develop the horizon grids. ArcGIS software was used to create
isopach grids, assimilate data products and perform interpretations in a single comprehensive
platform. Data products and maps were also generated to for use with this GIS platform.
Table 8. Software used in geophysical data processing.

The Edgetech SB-512 chirp system was used for sub-bottom profiling during this survey. Within
the towfish the chirp consisted of an electronic control bottle and a dual function transmitter-
receiver which interrogated the seafloor directly under the tow body. The SB-512 was towed with
a set of poly-balls to float the unit roughly 2 – 3 m below the water surface and ~75 ft behind the
vessel using a side davit and winch, and tethered to the Kevlar reinforced data cable (Figure 28).
The Edgetech 3200 deck-unit provided power and an Ethernet interface which connected to the
Discover software on the acquisition/control computer.

Software Function Version Manufacturer
HYPACK Navigation, cable out and navigation pass-through 2018 HYPACK
Surfer Gridding software 9 Golden Software
Discover SBP Chirp sub-bottom sonar interface and recording 37.0.1.109 Edgetech
SonarWiz Sub-bottom sonar processing and interpretation V7.00.0008 Chesapeake
Technology
ArcGIS Develop, mosaic and assimilate targets/features,
comprehensive interpretations 10.5 ESRI
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Figure 28. Photo showing the surface tow of the SB-512.
Following mobilization and prior to deployment, the system was powered up on the deck at 2%
power to check communications between the towfish and Discover. Before commencing the
survey, the system was deployed on site to test environmental performance, conducting several
test lines to determine the optimal system setup. During the test lines, the chirp sweep (frequency
range and pulse length), shot interval and the system power were all adjusted. Following the test
lines, settings were chosen to include a 30 millisecond (ms) sweep from 0.5-7 kHz at 100% power
and with a ping rate maximized for optimal resolution. The resolution and penetration of a sub-
bottom system are dependent on both the acoustic signal and the sediments encountered. The
selected settings were chosen as to identify potential sand sources with depth. The system
imaged 3 - 50 ft beneath the seabed through various continuous, semi-continuous, and paleo-
feature reflectors, showing the system’s adequacy for the requirements set forth in the SOW.
Detailed results from the sub-bottom sonar calibration can be found in Appendix B.

During the survey, sub-bottom data were continually monitored in the Discover software where
display-only gains could be applied to improve visualization. The towfish altitude was controlled
with a set of poly-balls to maintain the maximum altitude, which helped to keep the sea-surface
multiple as deep as possible in the sonar record. Layback was manually entered in HYPACK
software and did not change throughout the survey. Speeds were maintained around 3.5 kt. This
was important for the sub-bottom data quality to maintain an acceptable level of signal attenuation
in the water column and prevent unnecessary heaves (Figure 29).
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Figure 29. Screen capture showing typical sub-bottom sonar data acquisition in Discover.
The sub-bottom data were recorded in Discover software using Edgetech’s proprietary JSF
format. This format is preferred over the generic SEG-Y or XTF format because the JSF records
both the imaginary and real components of the raw signal.

Raw data quality was very high, with excellent signal-to-noise ratio (S/N). This permitted the
data to be processed using the following simple 4-step workflow:

Step 1 – JSF Import: Import JSF files with initial scalar to optimize full envelope to CSF
file in SonarWiz

Step 2 – Review Navigation and Bottom Track: Layback was analysed and adjusted
as needed using bathymetric surface to align with features in SBP. Seafloor was
bottom tracked to develop the surface for datum alignment.

Step 3 – Datum Alignment: Using the unclipped bathymetric surface for more
coverage, the bathymetric grid was used to “snap” the seafloor reflector to the grid,
removing the vertical offsets from the SBP profile.

Step 3 – Image Enhancement: Each line was reviewed to determine the optimal gain
and image settings, to provide the best contrast and enhancement of reflectors from the
surface to depth.

Step 4 – Develop Project: Cores were developed in cross section using available
stratigraphic/boring logs where profiles intersected positions of cores. Reflectors were
digitized while cross-referencing available core information and inspecting intersections.

Available cores have been added to the sub-bottom profiler imagery. To note, cores that may be
directly on one line but also close to the nearby intersecting survey line were applied to both
crossing lines for inspection.
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The SB-512 has a published vertical resolution of 8-20 cm and a penetration of 20 m in coarse
calcareous sands to 200 m in clay. Tuning the sonar for maximum penetration resulted in slightly
less vertical resolution; however, it produced excellent penetration, detecting features and
reflectors down 5 – 40 ft below the seabed. Increasing the acoustic energy in the water column
can also reveal artifacts from the sonar technology itself. In some areas, specifically where the
seafloor surface was more acoustically reflective, a towfish multiple can be seen around 50 – 60
ft below the seafloor; essentially a mirror of the towfish altitude. Other artifacts inherent to sub-
bottom sonars include ghosts and multiples. These artifacts are a result of sonars’ acoustic
energy reflecting off the seafloor, sub-surface horizons, the sea surface or towfish, and then off
the seafloor and horizons and back to the towfish. This inherent phenomenon imprints “ghost” or
“multiple” reflectors on the data due to the increased travel time, creating an apparent deeper
reflector as an artifact. An illustration of these effects can be seen in Figure 30. Towing the SBP
at the surface was the best approach to minimizing the potential masking by these acoustic
interferences.

Figure 30. Illustration of towfish geometry relative to the sea surface, showing the seafloor and
multiple ray paths.

Digitized reflectors were exported as X,Y,Z-Navd88 (reflector to seafloor surface) text files and
gridded into 50 ft resolution horizons and point feature classes in ArcGIS (Table 8). These
horizon grids were used to generate isopach grids depicting the thickness from the seafloor to
each respective horizon, therefore, these isopachs are irrelevant to any specific datum.
Contours were then developed from the isopach grids.

Towfish Ghost
Sea Surface Multiple
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Table 9. Attribute table generated for point shapefiles showing extents of digitized reflectors.
Field Description
OBJECTID ESRI auto-generated
Date Type of shapefile
Time Date and time of acquisition
Lat Latitude WGS84
Lon Longitude WGS84
X Starting X coordinate of line (NAD83 2011 NC
SPF)
Y Starting Y coordinate of line (NAD83 2011 NC
SPF)
Z_NAVD88 Elevation of reflector in NAVD88 (ft)

A polyline shapefile was also developed to show the towfish navigation,
“OIP2_SBP_JayBird_Navigation” and “OIP2_SBP_Central_Navigation” (Table 9). For interactive
analysis, these polylines have the SBP profile imagery attached to the feature class within the
geodatabase, similar to hyperlinks but embedded within the geodatabase so that links are not
broken when moving files. Using the “i” (Info) tool in ArcGIS software will reveal the attachment
to open. All images are labelled with distance along the line, with contacts labeled at the start
and end of the planned lines to indicate the Start of Line (SOL), End of Line (EOL), and the
cardinal direction of that start or end point. A feature class of the start points for each line is
provided and should be used in GIS referencing the direction of lines.
Table 10. Attribute table generated for the navigation tracklines shapefiles.
Field Description
OBJECTID Thickness in feet
Shape ESRI auto generated
Start_X X coordinate in NAD83 2011 NC SPF
Start_Y Y coordinate in NAD83 2011 NC SPF
Tiff Name of tiff image for that trackline
Shape_Length Length of polyline
Line_Name Simple line file name created for reporting

The following section outlines the survey results and products generated for the Oak Island, NC,
Phase 2 Geophysical Survey. The Jay Bird Shoals and Central Reach survey areas were
surveyed between 6/13 – 6/29/19 over 10 survey days. Both sites included full coverage
multibeam bathymetry and sub-bottom profiling, with side scan and magnetometer data only
being collected at the Jay Bird Shoals site. Results from these datasets are provided in the
following sections.

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4.1 Side Scan Sonar (Jay Bird)
The side scan sonar mosaic depicts both large scale and fine scale features, including a series
of fingering shoals extending from the N/NE and out to deeper water (Figure 31). The brighter
patches of seafloor usually represent fine scale sand waves, with wavelengths measured from 1
– 2 ft. Softer material, displayed as darker patches, often bounds these shoals in slightly
depressed channels.

A total of 49 side scan sonar targets were identified by Geodynamics in the Jay Bird Shoal survey
area. In addition, the TAR report identifies 11 targets, of which some are redundant and some
identify portions of a cable-like feature in the side scan data. Of these targets, seven were
identified as tires and the remaining as unkown debris / features. Most of the features were
relatively small objects, with the maximum height ~2 ft above the seafloor, maximum length of ~7
ft, and scouring on only five targets. A target report has been genearted and included in the
“Report” folder within the deliverable. These targets are also supplied as a point feature class
with target images attached to the feature class.

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Figure 31. Location maps of scan sonar targets across the Jay Bird Shoals survey area.
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4.2 Magnetometer (Jay Bird)
Nearly 85 nautical miles (NM) of magnetometer data was collected at Jay Bird Shoals. A total of
226 anomalies were identified (within the survey extents) by Tidewater Atlantic Research (Figure
32). Of these, eight had possible or confirmed associations with SSS features by Tidewater
Atlantic Research. Most of these were small scale and associated with debris. One significant
finding was a linear anomaly that struck SW-NE ran across the middle of the survey area, fading
away from detection in the deeper SW corner. Although the anomaly is unknown, it has been
advised by Tidewater Atlantic Research to be avoided (Figure 33).

Additionally, background gamma values data showed some variations between day to day. For
this reason, the digital terrain model (DTM) of the magnetic anomaly was generated from a
normalized dataset, meaning the spikes and background data noise were smoothed to generate
a normalized background value for each survey line, and subtracted from the real-time gamma
values, creating a X, Y, Gamma Spike dataset that could then be gridded at 20 ft resolution and
contoured (Figure 33). It should be noted that magnetic anomalies were depicted from the pre-
normalized dataset to avoid any potential skew of the gamma spike range and intensity values,
and the DTM is primarily supplied for visualization.

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Figure 32. Magnetic anomalies identified and provided by Tidewater Atlantic Research, Inc.
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Figure 33. Distribution of magnetic anomalies as seen from the gridded normalized gamma dataset, with a digitization of the observed
linear anomaly.
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4.3 Multibeam (Jay Bird & Central Reach)
Multibeam results reveal elevations from -14.67 to -29.51 ft, NAVD88 at Jay Bird and backscatter
intensities ranging from -11.10 to -48.60 db. The overall bathymetry of Jay Bird reveals shoaling
features paired with textural changes, with a patch of finer sediment on the west side of the survey
area (also deeper) (Figure 34, Figure 35).

At Central Reach, elevations range from -33.20 to -41.43 ft, NAVD88 and backscatter intensities
range from -15.19 to -44.81 db. The overall bathymetry reveals distinct sand ridges with a rather
homogenous bottom type. Additionally, there is evidence of former dredging (distinct, linear
changes in bathymetric relief), which caused an escarpment on the west side of Box 2. The
northern part of this escarpment has the lowest backscatter returns of the survey area (Figure 36,
Figure 37).

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Figure 34. Bathymetric surface for Jay Bird. The surface is overlaid with 1 ft contours and is at a 5 ft spatial resolution.
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Figure 35. Backscatter mosaic for Jay Bird. The mosaic is at a 5 ft spatial resolution.
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Figure 36. Bathymetric surface for Central Reach. The surface is overlaid with 1 ft contours and is at a 5 ft spatial resolution.
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Figure 37. Backscatter mosaic for Central Reach. The mosaic is at a 5 ft spatial resolution.
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4.4 Sub-bottom Sonar

Approximately 13 and 28.5 NM of sub-bottom profiler data were collected at Jay Bird Shoals and
the Central Reach area, respectively. Both sites were surveyed with the same settings and
configuration, with the exception of the sub-bottom being ~3-4 feet deeper in the water column
for the Central survey area. Available core data was used and applied to the nearest applicable
survey line and to multiple lines at intersections. Cores were color coded using an internal color
scheme to keep the comparisons of core units possible and their variability with respect to the
sub-bottom horizons interpretable (Figure 38). To preface for clarification, “reflector” refers to the
digitized break between “horizons”, which is described as the unit between the vertically bounding
reflectors. For each survey area, these are discussed from shallowest to deepest. Isopach grids
reference the thickness between the reflectors and the seafloor surface, therefore including the
thickness of the above horizons for successively deeper horizons. Horizon grids reference the
NAVD88 elevation of the gridded digitized reflector.

Figure 38. Color scheme used for core units at both Jay Bird and Central sites.

SW SW-SM SP ML SP-SM SM GC GP-GM GP
Well graded
sand
Well graded
silty sand

sand,
possible
shelly hash Sandy silt
Poorly graded
silty sand silty sand
Clayey
Gravelly Limestony Limestony
Rosy Brown OrangeRed Red SkyBlue Orange Yello Purple SeaGreen AliceBlue
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Figure 39. Sub-bottom profile navigation tracklines, with line and file names, start points, and arrow indicators for line direction for Jay
Bird.
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Figure 40. Sub-bottom profile data navigation tracklines, with line and file names, start points, and arrow indicators for line direction for
the Central area.
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4.4.1.1 Jay Bird SBP Description
The cores in the Jay Bird Shoal area are predominately some variation of poor to well graded
sands and some silty sand layers, all with varying shell content and variable thicknesses. To
note, although some units document limestone chips mixed in mid-core, these borings do not
document limestone or similar “cemented” material at their base to indicate a “depth to refusal”
on a hard substrate, nor does the sub-bottom record indicate a rock layer at the base of them.
Many of these cores show lenses or unit breaks in line with both the “shallow” and “mid” digitized
reflectors. The shallow reflector documents a mottled, variable, modern horizon in the sub-bottom
record, ranging from 2 – 8 ft thick to the surface (Figure 41). Cores mostly document a series of
multiple, thin units in the upper portions, consistent with a mottled acoustic record marking
variable densities. This unit is thickest towards the shoals and thins in the WNW portion of the
area.

Figure 41. The shallow, surface bounding horizon (blue) at the Jay Bird Shoal site. The faint
dashed green lines denote 10 ft depth intervals.
Below this horizon is the “mid horizon”, where cores still indicate variability in unit thickness and
content between each other, but the units are generally thicker than the upper units which
correlates well with the semi-clean acoustic signal documented between the mid and shallow
reflectors (Figure 42). This mid reflector is relatively faint in some areas but appears to match
breaks in core units and/or near the base of some. This unit is thickest near the shoals, and thins
towards the west, ranging from 5.5 – 21 ft thick (to the seafloor surface). This reflector marks an
unconformity that is not continuously lateral, but instead undulating as it marks this erosional
boundary. This unit and the above unit, although they have variability in grading, shell content,
and grain size spatially in both XY and Z, are mostly consistent with each other, and could present
a viable source for sediments if their overall content matches the requirements of the shoreface
to receive them.

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Figure 42. 3D image of showing the bathymetry overlaid on the profiles, showing the horizons
thin in deeper waters (blue) away from the shoal.
Below the mid horizon lies another horizon perched on a reflector marking an erosional surface,
labeled “base reflector” (light blue). This reflector is visible in the in the NE corner and is lost
below the sea surface multiple (dark purple) as it dips to the SW, ranging from 13 – 24.5 ft thick
(to the seafloor surface). The ringing acoustic signature of this reflector into the horizon below,
indicates the material may be acoustically impermeable and therefore compact, with only a few
paleo features and broad structures visible below. No cores penetrate through this unit (Figure
43).

Figure 43. The base reflector (light blue) in the E portion of the Jay Bird Shoals area.
North
North
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4.4.1.2 Central Reach SBP Description
In the Central Reach, most of these cores are relatively shallow compared to Jay Bird Shoals
cores and document a different depositional environment. These cores are mostly consistent in
their documentation of varying grades of sand, silty sand, sandy silt, trace shell content and/or
calcareous rubble. Nearly 25% of these cores document cementation and/or limerock fragments
at their base, with a few mid-units containing fragments of indurated material. Investigation of the
cores overlaid on the sub-bottom profiles reveals two laterally continuous horizons that are
consistent with unit breaks in the cores (Figure 44).

Figure 44. 3D view of the NE corner of the Central area displaying some of the characterizing
nature of the two depictable horizons.
The shallowest modern sediment lens is in the NE section of the eastern box of the Central area,
labeled Box 2. This “shallow horizon” was traced 1.5 – 7 ft thick over a fingering shoal feature.
Some portions of this reflector are faint and show little acoustical difference from the underlying
horizon, while some portions clearly reveal truncated strata at the base of the horizon, albeit
without a large contrast in acoustic signal. This is supported in the cores, as although they may
have many different units documented, they are only slight variations of each other. The cores in
this shallow unit mostly reveal poorly or well graded sand, silty sand, and varying trace shell
fragments.
East
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Figure 45. The eastern box of the Central survey area, showing the extents of the “shallow”
reflector (dark orange) in the NE corner over the shallowest portion of the survey area. Below, the
“base” reflector (lime green) marks the deepest, continuous reflector.
The second and underlying unit is similar to the shallow horizon in sediment content and variability
but has a much higher occurrence of limerock and/or calcareous content, either as fragments or
at the base of the cores. This is consistent with the SBP imagery, as many portions of this “base”
reflector mark a rugged, darker acoustic signal from the overlying strata, denoting a significant
change in density and or material. This base horizon is thickest in the eastern end of the survey
area and meets the surface at the most western extent of the survey area. It contains a few paleo
features and truncated strata, likely related to the reworked material in localized parts of the
horizon, as suggested by the high occurrence of limerock fragments and the rugged, undulating
nature. This is particularly noticeable in the survey data collected between the two boxes, as a
paleo channel underlies an escarpment, producing a pronounced surficial acoustic signal and
noisy horizon. Although most of this paleo feature is outside of the survey boxes, the additional
data collected helped to understand the overall geology and relationships between the bathymetry
and sub-bottom characteristics (Figure 46).

North
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Figure 46. 3D view of the northern end of the survey area, focused on the area between the two
boxes to show the paleo channel feature (tip of North arrow) that underlies the bathymetric
escarpment that extends from the western end of the eastern box (Box 2).
In addition, minimal acoustic penetration below this “base” reflector, even as it nears the seafloor
surface in the western survey area, suggests material below this reflector may be highly compact
and not as suitable for renourishment material (Figure 47).

Figure 47. 3D view of the Central area, showing the base reflector shoaling towards the surface in
the western part of the survey area with minimal acoustic penetration below the reflector.

North
North
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For both survey sites, the digitized reflectors were exported as X, Y, Z_NAVD88 point shapefiles.
These datasets were generated into 50 ft resolution grids and clipped to their respective data
extents to create the “horizon” grid. The multibeam bathymetry was subtracted from the
respective horizon grids to create the “isopach” grids, reflecting the thickness from the reflectors
to the seafloor surface. Contours were generated from the isopach grids (Figure 48).

Figure 48. Isopach grid and contours developed from reflectors digitized in sub-bottom profile
imagery.
To enhance the user experience for reviewing the sub-bottom profile imagery, three products
have been generated for multiple methods of review across various platforms. First, the profiles
were embedded within the geodatabase, attached to each profiles respective navigation trackline.
To review these profiles, the user can use the “i”, Info tool in ArcGIS software to view the
attachments (Figure 49). Sub-bottom profile images are marked with 1,000 ft distance intervals,
10 ft vertical intervals, and have been labeled with contacts to denote the start and end of the
planned line files with the cardinal direction labeled for referencing the map. A feature class
marking the start point of each line was generated to help comprehension of data coverages.

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Figure 49. View of the ArcGIS platform with the embedded profiles accessible as attachments by
clicking the trackline with the “i” tool.

Second, these GIS products were combined into an interactive PDF, constructed with hyperlinks
to each respective sub-bottom profile. The profile images contain links back to the main map
page in the bottom left corner (Figure 50).

Figure 50. Hyperlinked PDF of sub-bottom profile imagery, with start and end of lines marked
along with the cardinal direction of that start/end point.

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Third, a 3D interactive web page was generated during processing, allowing the user to pan, tilt,
zoom, and vertically exaggerate the sub-bottom profile fence diagram.

Figure 51. 3D interactive web page, allowing pan, tilt, zoom and vertical exaggeration.

The data collected for the Phase 2 geophysical and hydrographic survey are comprehensive to
investigate beach renourishment resources. The bathymetry datasets capture the overall relief
and trend of geomorphological features while the backscatter and SSS data help provide a
textural context to these features. The combination of SSS and MAG data provide valuable
information to identify potential objects that may have an influence on dredging or planning efforts.
The sub-bottom profiler data images below the depth of cores in both survey areas, providing
detailed information relative to the observed core units and their distribution both vertically and
horizontally. The MAG and SSS data reviewed by Tidewater Atlantic Research found many
magnetic anomalies at Jay Bird Shoals, however, there was no indication of culturally significant
anomalies based on size and duration of signatures. These datasets have been synthesized for
review in a single desktop application, ArcGIS. For a more comprehensive analysis of the sub-
bottom imagery, a 3D fence diagram can be viewed and manipulated via a web browser. A
README is provided to illustrate the structure of the deliverable items included within this
Deliverable. For any question, please contact Geodynamics directly.
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Survey Scope of Work (SSOW)
June 2019 – October 2019

Client(s)
Moffatt & Nichol / Town of Oak Island
Description of Work
This is the second phase of geophysical surveys for Moffatt & Nichol in support of future re-
nourishment efforts on Oak Island, NC. This phase includes 2 areas inside of the 3 nmi state
waters area, therefore, the surveys follow NC state guidelines. These surveys will make use of
multibeam sonar (MBES), side-scan sonar (SSS), marine magnetometer (MAG), and sub-bottom
profiling (SBP). This work entails a full survey report and geophysical assessment of the data
acquired.
Survey Area(s)
Surveys will take place at 2 main areas outside Wilmington Harbor. The “Jay Bird” site is surveyed
for complete coverage MBES and SSS along with 100 ft spaced MAG and a grid of SBP data.
The “Central Reach” site includes the same survey scheme, however, excludes MAG and SSS
data collection because this work was previously completed for Phase 1. Images illustrating the
survey areas and line plans can be found in Section 6 of this SSOW.
Horizontal Coordinate System
NC State Plane (NAD83-2011)

Horizontal Coordinate System Units
US Survey Feet

Vertical Coordinate System
NAVD88 (Geoid12b – Grid 7)

Vertical Coordinate System Units
US Survey Feet (Elevations)

Methodology
Real-time horizontal and vertical corrections are provided by Real-time Kinematic (RTK) North
Carolina CORS Virtual Reference Station (VRS) Network. When the Real-time VRS network is
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not available (no internet connection), corrections will be provided by DGPS. MBES data should
be corrected in post-processing by POSPac. Towed sensors will be positioned by layback
techniques.

Standards/Requirements
Data acquisition requirements should be guided by this SSOW such that data are deemed of high
enough quality for preliminary geotechnical and cultural investigations.
Survey Method: (Multibeam Sonar – Both Sites)
Purpose
MBES data is being acquired to determine accurate depths at potential borrow areas and aid in
SBP data processing (vertically align the seafloor surface of the sub-bottom profile to the
bathymetry). The survey design will be developed with full coverage bathymetry as the primary
goal. While backscatter data is concurrently acquired with the bathymetry, it is not a specific
component of this project, but may be provided to aid in analysis (not required).

Accuracy Requirements
MBES survey shall follow guidelines specified in the IHO-S44 for Order 1a surveys.
Patch test performed and documented for the survey vessel
Full Coverage MBES to provide the highest possible resolution
Minimum 2 SVP/day
Collection of cross-line data

Coverage Requirements
MBES data shall be 100% bottom coverage at both sites. Line spacing shall provide enough
overlap as to acquire ~130% coverage and density to support a full coverage surface.
Survey Method: (Side Scan Sonar – “Jay Bird” Only)
Purpose
SSS data is being acquired for object detection, identification of hard bottom areas and general
characterization of the seafloor at “Jay Bird”. Side scan data will be used in concert with the MAG
data for determination of objects and cultural assessments. SSS data will be processed by
Geodynamics and additional SSS targets may be identified by Tidewater Atlantic Research. SSS
in the “Central Reach” site was collected previously in Phase 1 and was therefore not a
component of the Phase 2 survey.

Accuracy Requirements
SSS layback review for position verification

Coverage Requirements
Full coverage SSS mosaic at highest allowable resolution

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Survey Method: (Marine Magnetometer – “Jay Bird” Only)
Purpose
MAG data is being acquired for object detection. MAG data will be used in concert with the SSS
data for determination of objects and cultural assessments. Magnetic anomalies are to be
processed and interpreted by Tidewater Atlantic Research and included within the final survey
report and deliverable package. MAG in the “Central Reach” site was collected previously in
Phase 1 and was therefore not a component of the Phase 2 survey.

Accuracy Requirements
Position verification via SSS layback verification (Mag fixed length behind SSS)

Coverage Requirements
Line spacing of 100 ft
Survey Method: (Sub-bottom Profiling – Both Sites)
Purpose
Sub-bottom profiler data is being acquired to determine the shallow sediment distribution and
identify subsurface features. SBP data will be used in concert with the MBES data for
identification of subsurface sediments and geologic interpretations.

Accuracy Requirements
Performance Report (environmental calibration)

Coverage Requirements
Line spacing to create a 100 ft grid pattern
Data & Reporting Deliverables
Listed below are deliverables associated with each type of data acquisition and cumulative
components for the project. This project contains full processing, analysis, GIS package, and
reporting.

Data Type Data Product Data Format Notes
Bathymetry Data
Bathymetric Elevations ASCII TXT XYZ Data 2 decimal precision
Bathymetric Contours ESRI Feature Class Contour interval TBD by data
quality (~1 ft)
Bathymetric Surface ESRI Raster Dataset Resolution TBD by data
quality/density (~5 ft)

Magnetometer Data
MAG Anomalies ESRI Feature Class /
ASCII TXT XYZ Data
Include: latitude/longitude,
eastings/northings, sensor
reading, sensor
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Depth, size when applicable,
and interpretation (Jay Bird
Only)
MAG Navigation ESRI Feature Class /
ASCII TXT XYZ Data
All processed MAG data
including latitude/longitude,
eastings/northings, sensor
reading
MAG Anomaly Surface ESRI Arc Grid Resolution determined in
processing
MAG Anomaly Contours ESRI Feature Class Polyline

Side Scan Sonar Data
SSS Targets ESRI Feature Class linked
with SSS target PDF
sheets
Include: latitude/longitude,
eastings/northings, range,
depth, height above seabed,
size, and interpretation
SSS Mosaic GeoTiff 3 Band

Sub-bottom Profile Data
Processed SBP Data Tiff SBP Profile with digitized
reflectors
SBP Navigation / Tracklines ESRI Feature Class /
ASCII TXT XYZ Data
Profile imagery embedded as
attachment
SBP Line Start/End Points ESRI Feature Class /
ASCII TXT XYZ Data

SBP Lines PDF Illustration of SBP data with
contacts and navigation map
Isopach Surface 1, 2, 3…. ArcGIS Grid / Grid XYZ
Data
Isopach Surface from digitized
reflector

Cumulative GIS Files (when applicable)
Point Features of Interest ESRI Point Feature Class Include: latitude/longitude,
eastings/northings,
and interpretation
Line Features of Interest ESRI Line Feature Class Include: length
and interpretation
Polygon Features of Interest ESRI Polygon Feature
Class
Include: area
and interpretation
Processing Specifications / Notes
MBES Data should be post-processed for improved navigation and GPS Tides
MAG data for “Jay Bird” will be processed / analyzed by Gordon Watts at Tidewater Atlantic
Research. Additionally, Gordon Watts may identify additional SSS targets.
SBP data will be “snapped” to the NAVD88 MBES Bathymetry

Horizontal Coordinate System and Units
All data will be provided in NC State Plane (NAD83-2011) US Survey Feet coordinates.

Vertical Coordinate System and Units
MBES and SBP data will be vertically referenced to NAVD88 (Geoid12b – Grid 7) and provided
in US Survey Feet.
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Reporting
Full Survey and interpretive report including description of findings for each survey component
and cumulatively for each region.
Report to contain QA-QC documentation including but not limited to MBES cross-line analysis,
MBES chart comparison, SSS feature alignment as well as the applicable ancillary QA-QC
components, and identification of any SBP artifacts/multiples that need descriptions.
Ancillary Components (Appendices in Report or Submitted as Separate Documents
in the Deliverable)
Daily Field Notes
SSS Position Verification documentation
MBES Patch / Verification documentation
SBP Performance Verification document
Vessel & Equipment Specs / Integration documentation
Delivery
Data will be delivered on portable hard disk drive(s) or Digital Video Discs (DVDs) and made
available via secure file transfer if necessary. Raw MBES, SSS, MAG, and SBP data will be
maintained by Geodynamics and made available upon request.
Points of Contact

Katie Finegan, PE (Main POC and project delivery)
[e-mail]
Moffatt & Nichol
4700 Falls of Neuse Road, Ste 300 | Raleigh, NC 27609
P 919-781-4626 ext.12152
D 919-645-0652
M 828-550-7272

Additional Contacts (to be included in project related communications):
Katie Finegan (main)
Jeff Crump [e-mail]
Brandon Grant [e-mail]
Mark Pirrello [e-mail]

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Gordon P. Watts, JR., PH.D, RPA (Archaeological / Cultural Investigation)
Tidewater Atlantic Research (TAR)
P.O. BOX 2494
5290 river road [shipping only]
Washington, NC 27889-2494
P 252-975-6659

Dave Bernstein (Project Manager)
[e-mail]
Geodynamics
310 A Greenfield Drive
Newport, NC 28557
P 252-247-5785
M 252-422-8428

Ben Sumners (Survey Team Lead)
[e-mail]
Geodynamics
310 A Greenfield Drive
Newport, NC 28557
P 252-247-5785
M 252-475-4710

Eric King
Southport Marina

606 W. West Street

Southport, NC 28461
P: 910-457-9900
M 910-508-8762
Dates of Importance
Deliverable(s) Due
Deliverable completed and submitted by 10/08/19
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C.1 - Multibeam Patch Test Document

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C.2 - Sub-Bottom Calibration Document

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C.3 - Side Scan Sonar Calibration Document

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C.1 Cross-line Analysis
A cross-line analysis was performed by comparing the final bathymetric surfaces, which use only
main-scheme lines, with surfaces containing only cross-lines. The two surfaces are differenced,
and the results are outlined in Figure 52 and Figure 53. It should be noted that large values for
min/max differences are heavily influenced by the cross-line only surfaces. These cross-line only
surfaces were not cleaned as a standalone product, which would be necessary because CUBE
surface generation relies heavily on adjoining data (density). These cross-line surfaces do not
have many, if any, adjacent lines, therefore the CUBE is generating a surface on less hypothesis,
so fliers are more prevalent in the cross-line only surfaces. Overall, cross-lines are not included
in the final surfaces and are not submitted in the deliverable, therefore, the cross-line surfaces
were left as is and the large max/min values are attributed to such. The more meaningful
information lies in the mean and standard deviation, which show agreement between the cross-
line and main scheme surfaces (Figure 52 and Figure 53). Additionally, examples of cross-line
to main scheme data alignment in a cross-sectional 2D view can be found in Figure 54 and Figure
55.

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Jay Bird

Figure 52. Cross-line to main scheme surface comparison at Jay Bird. Since the cross-line only
surface is not a deliverable and cross-lines are not included in the final bathymetric surface, fliers
may exist in this surface. Therefore, the large min/max values can be attributed to these fliers/the
lack of data for CUBE generation in the cross-line only surface. The mean (0.00 m) and standard
deviation (0.06 m) are the more meaningful results. Note the statistics are in meters.

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Central Reach
Box 1 (Eastern)
Box 2 (Western)

Figure 53. Cross-line to main scheme surface comparison at Central Reach. Since the cross-line
only surfaces are not a deliverable and cross-lines are not included in the final bathymetric
surface, fliers may exist in this surface. Therefore, the large min/max values can be attributed to
these fliers/the lack of data for CUBE generation in the cross-line only surfaces. The mean (0.00
m, 0.03 m) and standard deviation (0.06 m, 0.04 m) are the more meaningful results. Note the
statistics are in meters.

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Jay Bird

.

Figure 54. The yellow slice within the red box (top view) is illustrating the data displayed in the 2D
subset view (bottom image). In the 2D subset view, the tan soundings represent the cross-line,
while all other main scheme lines are displayed in various colors. The data is exaggerated to 20X
and shows good agreement.

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Central Reach

Figure 55. The yellow slice within the red box (top image) is illustrating the data displayed in the
2D subset view (bottom image). In the 2D subset view, the light blue soundings represent the
cross-line. The data is exaggerated to 20X and shows good agreement

C.2 Junction Analysis
At Jay Bird, Geodynamics had existing multibeam data in the area from a previous project in
2015. This 2015 multibeam data was collected by the R/V Benthos and was compared to the
2019 R/V 4 Points data collected for this project. The two bathymetric surfaces were compared
and showed agreement between datasets with a mean difference of 0.02 m and of standard
deviation of 0.12 m. This gives confidence in the dataset. It should be noted that many of the
differences could be attributed to natural change due to sediment transport. This is a dynamic
area near an inlet with higher currents and wave energy, therefore, natural change is likely
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between a span of four years. Figure 56 below displays the difference surface along with the
statistics generated from the differencing. Note the statistics and surface are in meters. This is
because the multibeam processing software utilizes meters and the transformation of the data to
feet happens in ArcGIS after exportation from the multibeam processing software.
Jay Bird

Figure 56. Displaying the difference surface derived from differencing 2015 R/V Benthos
multibeam data from the 2019 R/V 4 Points data. The graph displayed in the upper left potion of
the figure shows the statistics generated from this differencing. Overall, the data shows
agreement between datasets.

C.3 NOAA Chart Comparison
For Central Reach, the final bathymetric surface was compared to the NOAA nautical chart in the
area. To do this comparison, the 2019 Central Reach data was transformed to MLLW (chart
datum) using a transformation value of 3.02 ft (derived from NOAA Vdatum). The data was then
compared to nearby soundings on the chart. An example of this comparison is displayed below
in Figure 57. Overall, the data agreed with the NOAA charted soundings. It should be noted that
NOAA has a particular methodology to select which soundings go on the chart, as to reflect the
shoalest soundings in the region. Additionally, most of the data used for this chart was not recent
data.
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Central Reach

Figure 57. NOAA chart comparison in the Central Reach. The 2019 data was transformed to
MLLW (using NOAA Vdatum) for this comparison. In CARIS, the mouse is hovered over the
charted sounding and the white information bar displays the value attributed to the bathymetric
surface. Overall, the datasets show agreement.