HomeMy WebLinkAboutAttachment 4 - Radio Island Beach Fill Survey Report Geodynamics, an NV5 Company
310 Greenfield Dr., Suite A,
Newport NC 28570
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1.0 Introduction ......................................................................................................... 1
Project Description ....................................................................................................... 1
Project Area ................................................................................................................. 1
Report Purpose ............................................................................................................ 3
2.0 Survey Approach ................................................................................................. 3
Equipment ................................................................................................................... 3
2.1.1 Vessel ................................................................................................................... 3
2.1.2 Hardware .............................................................................................................. 4
2.1.3 Software ............................................................................................................... 5
Geodesy ...................................................................................................................... 5
Project Schedule and Weather..................................................................................... 6
3.0 Methodology ........................................................................................................ 8
Acquisition ................................................................................................................... 8
3.1.1 Navigation and Sensor Positioning ....................................................................... 8
3.1.2 Bathymetry ........................................................................................................... 8
3.1.3 Topographic Elevations ........................................................................................ 8
Processing ................................................................................................................... 9
3.2.1 Bathymetry ........................................................................................................... 9
3.2.2 Topographic Elevations ........................................................................................ 9
3.2.3 Digital Elevation Modelling .................................................................................... 9
Quality Assurance and Quality Control ........................................................................10
4.0 Results ............................................................................................................... 11
4.1.1 Bathymetry ..........................................................................................................11
4.1.2 Topographic Elevations .......................................................................................13
4.1.3 Digital Elevation Modeling ....................................................................................15
5.0 Discussion ......................................................................................................... 19
6.0 Appendix ............................................................................................................ 20
Multibeam Sonar – Patch Test ....................................................................................20
Survey Control ............................................................................................................22
Sediment Samples ......................................................................................................23
Scope of Work ............................................................................................................40
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List of Figures
Figure 1. Survey extents for the topographic and bathymetric elevations. .................................. 2
Figure 2. RV 4Points .................................................................................................................. 3
Figure 3. VDatum online settings for converting Geoid12b data to Geoid18. .............................. 5
Figure 4. Tides throughout the survey. ....................................................................................... 6
Figure 5. Barometric pressure throughout the survey. ................................................................ 6
Figure 6. Air temperature throughout the survey. ....................................................................... 7
Figure 7. Wind speed and direction throughout the survey. ........................................................ 7
Figure 8. Statistics of the difference values from the UAV LiDAR elevations subtracted from the
2m rod elevations across profiles. .............................................................................................10
Figure 9. Statistics of the difference values from the bathymetric surface elevations subtracted
from the 2m rod elevations across profiles. ...............................................................................11
Figure 10. Statistics of the difference values from the bathymetric surface elevations subtracted
USACE singlebeam soundings collected on 7/20/21. ................................................................11
Figure 11. Multibeam bathymetry survey extents and results. ...................................................12
Figure 12. Topo-bathy profile data developed from 2m rod RTK shot points and the bathymetric
surface. .....................................................................................................................................14
Figure 13. Digital Elevation Model of the LiDAR, multibeam bathymetry, and alongshore XYZ shot
points. .......................................................................................................................................16
Figure 14. Map of LiDAR and multibeam bathymetry extents and the XYZ shotpoints collected to
aid the modeling process, highlighting the area of interpolation. ...............................................18
Figure 15. Statistics comparing 2m shot points on Profiles 1 – 4 within the interpolated area to the
elevations from the digital elevation model. ...............................................................................19
List of Tables
Table 1. General Vessel Specifications of the R/V 4-Points. ...................................................... 3
Table 2. A list of all hardware used for topographic and bathymetric data acquisition. ............... 4
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Project Description
Geodynamics was contracted by Moffatt and Nichol to perform a shoreline hydrographic and
topographic survey of approximately 2,850 ft of shoreline along Radio Island next to Gallants
Channel, Beaufort, NC. This survey included recording elevation data across 5 profiles,
multibeam echosounder (MBES) bathymetry nearshore, Light Detection and Ranging (LiDAR)
and orthoimagery data collected by a UAV for topographic elevations, and XYZ scatter data along
the lower extents of the shoreface in between the extents of the LiDAR and bathymetry. The
datasets were ultimately combined to generate a comprehensive topo-bathy digital elevation
model (DEM). Additionally, 4 – 5 sediment samples were collected across morphologic zones
along the profiles for sediment analysis.
Project Area
The survey area is oriented north-south along 2,850 ft of the Gallants Channel bounding shoreline
of Radio Island in Beaufort, NC.
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Figure 1. Survey extents for the topographic and bathymetric elevations.
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Report Purpose
This report provides a description of survey conditions, equipment, acquisition and processing
methodologies, and an overview of survey results.
Equipment
The RV 4Points was used for acquiring MBES data.
Figure 2. RV 4Points
Table 1. General Vessel Specifications of the R/V 4-Points.
General Vessel Specifications
Vessel name R/V 4Points
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: Bucket
Max Speed: 30 knots
Min. Survey Speed: 2.5 knots
Propulsion: 2 x 150 HP Yamaha Outboard Motors
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Auxiliary Power: 5kW Fischer Panda Generator
Fuel Cap.: 120 gallons
GPS: 2 x Simrad NSS Series
Magnetic Compass: Richie
Radar: Lowrance Broadband
Autopilot: Simrad AP-28
VHF: ICOM 504
Internet: Verizon 4G LTE JetPack
The following equipment was used for acquiring topographic and bathymetric elevations.
Table 2. A list of all hardware used for topographic and bathymetric data acquisition.
Hardware Equipment Function Manufacturer Model Navigation & Attitude 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 540AP
Secondary GPS-GNSS
Antenna (starboard) Position/Attitude/Heading Trimble/
Aeroantenna 540AP
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
Leica Smartnet RTK Corrections Leica RTCM 3 Topography Receiver XYZ Trimble R10
Survey Rod Fixed height measurement Trimble
2m w/flat base
on land and
point base for
benchmarks
Controller Recording Receiver data Trimble TSC3 MBES 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 Base X2
2 Sonar Heads Bathymetry Kongsberg 2040C-Dual
Head
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Geodesy
All survey data received corrections and/or was referenced with the NC Real Time Network
correction service, and either recorded in NAD83(2011) NC State Plane Feet using Geoid18 or
post-processed using Geoid18 and converted to NC State Plane Feet. Vdatum online was used
to convert topographic elevations from Geoid12b to Geoid18.
Figure 3. VDatum online settings for converting Geoid12b data to Geoid18.
Software Function Version Manufacturer
Qinsy Navigation 9.3.1 QPS
SIS Recording, plotting, and controlling multibeam
echosounder 4.3.2 Kongsberg
SeaCast Recording sound velocity profile data 4.2 AML
POSView Recording vessel/sensor attitude and
positioning 10.5 Applanix
Surfer Gridding XYZ datasets 9 Golden
Software
Hypack Planning and merging topo-bathy datasets 2019 Xylem
ArcGIS Pro Plan and develop deliverable products 2.8.0 ESRI
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Project Schedule and Weather
All survey activities took place on 7/20/21. Topographic data, including UAV flight was collected
in the morning during low tide. However, rain and mist prevented the UAV flight from being
performed at the lowest tide possible. Bathymetry data were collected in the afternoon during
peak high tide to maximize shoreward coverage. The following figures illustrate tide and
meteorological conditions for the duration of the survey.
Figure 4. Tides throughout the survey.
Figure 5. Barometric pressure throughout the survey.
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Figure 6. Air temperature throughout the survey.
Figure 7. Wind speed and direction throughout the survey.
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Acquisition
All spatial data were collected using DGNSS corrections from the North Carolina Real Time
Network (NC RTN) service. This service provides differential corrections over the internet to
obtain survey-grade accuracies using the NAD83(2011) ellipsoid. Although the data were
recorded with Geoid12b to reduce ellipsoid elevations to NAVD88, the data were post-processed
with Geoid18 or converted using VDatum as necessary.
Multibeam soundings were precisely positioned using the Applanix POS MV v5 Inertial-aided
navigation system for position, heading, attitude, heave and velocity in realtime and post-
processing. Attitude and navigation data for a mutual location near the transducers were provided
to the acquisition software, SIS, to be precisely co-referenced in terms of position and orientation
so that each transducer in SIS would appropriately record heave, pitch, and roll corrected
soundings with DGNSS quality positions with respect to the vessel reference frame defined in the
POS MV configuration. This information was also recorded through POSView, the POS MV
controller software, and used in post-processing to recompute GPS heights and positions in the
event that accuracies were degraded.
All offsets, orientations and settings were defined or verified prior to survey operations. A patch
test was performed prior to the survey to define and verify any potential biases in the
comprehensive integration between the vessel reference frame and the transducers’ orientations.
A patch test document can be found in the Appendix.
Multibeam bathymetry was recorded in SIS software. The EM-2040c DH system was operated at
300 kHz, equidistant beam spacing and angles between 72 - 80̊ to maximize coverage over
adjacent slopes or features when necessary. Qinsy software was used for navigation and
verification of coverage across the survey extents. A sound velocity cast was performed on site
before any acquisition and integrated in realtime for accurate beamforming through the water
column. A MicroSV sensor mounted at the transducers allowed monitoring of realtime surface
sound velocities with respect to the profile values at that depth (~0.8 m). Sound velocities
remained constant, and one cast was used for the survey. Survey speeds were maintained
around 3-4 kts to safely navigate the vessel traffic, current, jetties, and potential shoreline features
that complicate navigation. This also allowed for excellent data density across the jetties and
bedform features throughout the channel.
Topographic elevations were collected using a TSC3 and a Trimble R10 on a 2m survey rod with
a flat base to accommodate the sand. Prior to data acquisition, this system was used with a point
base to verify the alignment of the NC RTN correction service with a nearby NC Geological Survey
(NCGS) benchmark, “Betty” (see Survey Control Report in Appendix).
Across the profiles, data were collected at ~3 ft intervals or at breaks in morphology from either
the start of the profile or to the extents of access. Given the weather conditions that had prevented
the UAV from acquiring LiDAR data at peak low tide, a series of XYZ shot points were collected
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along the shoreline at a lower depth to fill in gaps in coverage between the UAV and bathymetry
data.
Processing
Bathymetry data were processed using CARIS HIPS software and POSPac software. POSPac
provided a platform to post-process the attitude and navigation data for a few instances of
dropouts in the NC RTN service and compute a smoothed best estimate of trajectory (SBET) to
override the realtime records in HIPS. This process used the same nearby CORS station that
provided realtime DGNSS corrections to reintegrate the recorded raw satellite and ephemeris
data with the raw vessel navigation and attitude stored in the POSPac file. HIPS integrated the
positions and attitude correctors and the GPS Height from the SBET to reduce the soundings
from the NAD83(2011) ellipsoid to NAVD88 orthometric elevations using Geoid18, and finally
compute a projected surface in NC State Plane coordinate reference system. The surface and
swath data were reviewed in 2D and 3D subsets where erroneous soundings or artifacts were
removed from the dataset. The final surface was computed at 3 ft resolution and exported for
further development in ArcGIS software. One-foot contours were generated and used to further
review the dataset for logical consistency of the contours and any potential misalignments of the
overlapping swath dataset. The XYZ points were extracted in ArcPro to produce an XYZ dataset
item to integrate into a digital elevation modeling (DEM).
Hypack was used to merge the gridded cell values to the planned profile lines in Hypack software
to generate points with a “distance from baseline” (DBL) value; a distance interval computed from
the start of the planned survey line. Profile data were converted to a shapefile and ASCII file,
including the following fields: Profile Location, Profile Number, X, Y, Z_NAVD88, and Method
(Topo vs. Hydro).
Topographic data were set to only record when RTK accuracies were met in the TSC3. All data
were exported as an XYZ dataset and converted from NAD83(2011) NC SPF using Geoid12b to
elevations with Geoid18 using VDatum Online. Profile data were merged onto the profile lines in
Hypack software to generate DBL values. Profile data were then converted to a shapefile and
ASCII file, including the following fields: Profile Location, Profile Number, X, Y, Z_NAVD88,
Distance from Baseline (DBL) and Method.
Scatter XYZ data collected alongshore were exported as an XYZ dataset to integrate in the DEM
process and provided as a point shapefile.
To remove any false depths below the water level at the time of the UAV survey, orthoimagery
recorded during the flight was used to clip the LiDAR grid at the water line alongshore. The grid
was exported to provide as an XYZ dataset and for integration into a comprehensive DEM.
Development of the model included XYZ data from the clipped LiDAR grid, the bathymetry
surface, and the nearshore scatter data collected alongshore. The dataset was gridded at 3 ft
using a Kriging algorithm and clipped based on the extents of combined extents of the individual
datasets. Contours were developed at 1ft intervals and provided as a shapefile.
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Quality Assurance and Quality Control
In addition to pre-survey QAQC measures, individual datasets were reviewed and compared to
each other and third-party datasets.
The first step was verifying the NC RTN service with published benchmarks to ensure proper
configuration and operation of the network service (see Survey Control Report). With this verified,
we compared all other datasets to the 2m rod heights. Considering the 2m rod collected XYZ
points over sand with a flat base, both the LiDAR and bathymetry datasets computed mean
differences of less than 0.1 ft.
Figure 8. Statistics of the difference values from the UAV LiDAR elevations subtracted from the
2m rod elevations across profiles.
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Figure 9. Statistics of the difference values from the bathymetric surface elevations subtracted
from the 2m rod elevations across profiles.
Additionally, the USACE performed a singlebeam echosounder survey of the Bulkhead Channel
Ranges 1-2A on the same day. This data overlapped with the bathymetry survey to provide a
verification of the recorded data. Statistics of the 3 ft bathymetric surface compared to the
individual singlebeam soundings reveal a mean of less than 0.1 ft.
Figure 10. Statistics of the difference values from the bathymetric surface elevations subtracted
USACE singlebeam soundings collected on 7/20/21.
Computing Total Propagated Uncertainties is a valuable metric to theoretically assess accuracies.
Additional methods include using ground-truthed datasets, such as that from the 2m rod and
comparing to validated, third-party datasets from vendors such as USACE. The series of statistics
computed herein using data results and comparisons across multiple data types, vendors and
platforms indicates the accuracy of the survey data meets and exceeds the accuracy of the survey
requirements in accordance to EM 1110-2-1003 standards.
The multibeam bathymetry survey spanned depths from -39’ to -1.9’ nearshore. The surface
captures the nearshore berm, sand waves, and the jetty structure. Data were not collected behind
the jetty between the structure and the shoreline due to safety. The 3 ft bathymetric surface
compared well to the topographic profile data and USACE singlebeam soundings to a mean of
less than 0.1 ft.
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Figure 11. Multibeam bathymetry survey extents and results.
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Topographic profile data captured the breaks in morphology and overlap with both the LiDAR and
bathymetry data with excellent agreement with a mean value less than 0.1 ft. The alongshore
XYZ dataset provides elevations that assisted in the DEM development. To extend the depth of
the profiles, elevations from the bathymetric surface were extracted for the seaward extents.
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Figure 12. Topo-bathy profile data developed from 2m rod RTK shot points and the bathymetric
surface.
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The comprehensive DEM is a combination of the LiDAR, multibeam bathymetry, and alongshore
XYZ shot points. Contours do not cross each other and gaps between the datasets interpolated
well.
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Figure 13. Digital Elevation Model of the LiDAR, multibeam bathymetry, and alongshore XYZ shot
points.
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Due to safety concerns, the RV 4Points was not able to access the area between the jetty and
the shoreline. XYZ shot points were collected to assist in gridding. The interpolated area appears
natural with no crossing contours but does show deviations from the elevations recorded on
Profile 5 from 0.5 to -2 ft and should be considered as a “best interpolation” area.
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Figure 14. Map of LiDAR and multibeam bathymetry extents and the XYZ shot points collected to
aid the modeling process, highlighting the area of interpolation.
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Elsewhere alongshore where the interpolated gap between the two datasets is smaller, the
elevations from the topo data on Profiles 1 – 4 is more consistent with the modeled elevations,
showing a standard deviation of 0.23 ft and a mean less than 0.1 ft for the elevation differences
from within this gap. A polygon of this interpolated region as seen in Figure 14 is provided in the
deliverables for guidance on usage of the comprehensive DEM. Another potential source of these
deviations is the DEM resolution of 3 ft will not reproduce the same resolution of single shot points,
especially when taken across breaks in morphology.
Figure 15. Statistics comparing 2m shot points on Profiles 1 – 4 within the interpolated area to the
elevations from the digital elevation model.
These individual datasets provided meet or exceed the standards set forth in the EM 1110-2-1003
and CETN II-38 documents and satisfy the requirements listed in the Technical Standards for
Beach Fill Projects document 15A NCAC07H.0312. The comprehensive DEM accurately displays
elevations for all areas of data coverage and interpolated areas match closely to ground-truthed
elevations with the exception of the larger gap between the jetty and shoreline where access was
a safety concern. Analysis of sediment samples can be found in the Appendix. The information
regarding methodology and quality control for the LiDAR and orthoimagery collected by the UAV
will be provided in a separate report.
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Multibeam Sonar – Patch Test
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Survey Control
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Sediment Samples
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Scope of Work
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