Coastal Single-beam Bathymetry Data Collected in 2022 off Seven Mile Island, New Jersey

GNSS Acquisition: Two Global Navigational Satellite Systems (GNSS) base stations were established on NGS benchmarks in which the roving vessels would be within 12-15 kilometers (km) of the base station at a given time. The primary benchmark JU04 (PID: JU0450) was located approximately in the middle of the survey extent where the secondary base station DP15 (PID: DP1533) was located to the northeast. The base stations were continually occupied and equipped with a Spectra Precision SP90M GNSS receiver recording full-carrier-phase positioning signals from satellites via Trimble Zephyr 3 Base GNSS antennas recording at a rate of 0.1 second (s).

Single-Beam Bathymetry Acquisition: The single-beam bathymetric data collected under the USGS Field Activity Number (FAN) 2022-309-FA, include two separate survey platforms; a floating seismic-sled towed by the R/V Sallenger (SLED - subFAN 22BIM03), and the R/V CHUM (WVR2 - subFAN 22BIM05), a 12-ft (foot) Yamaha PWC. The SLED collected 135.48 line-km (288 lines) and the WVR2 collected 145.46 line-km (60 lines). Boat motion was recorded at 50-millisecond (ms) using a SBG Ellipse A motion sensor. HYPACK A Xylem Brand (version 21.0.2.0), a marine surveying, positioning, and navigation software package, managed the planned-transect information and provided real-time navigation, steering, correction, data quality, and instrumentation-status to the boat operator. Depth soundings were recorded at 50-ms intervals using an Odom echotrac CV100 echosounder with a 4-degree, 200-kilohertz (kHz) transducer. Data from the GNSS receiver, motion sensor, and echosounder were recorded in real-time aboard all vessels independently and merged into a single raw data file (.RAW) in HYPACK, with each device string referenced by a device identification code and time stamped to Coordinated Universal Time (UTC). Sound velocity profile (SVP) measurements were collected using SonTek Castaway Conductivity, Temperature, and Depth (CTD) instruments. The instruments were periodically cast overboard to record changes in water column speed of sound (SOS). A total of 202 successful sound velocity casts were collected and ranged in depth from 0.15 to 3.26 m, and in sound velocity from 1490.30 to 1490.59 meters per second (m/s).

Differentially Corrected Navigation Processing: The NGS horizontal published numbers for Permanent Identifier (PID) JU0450, stamping STONE HARBOR 1932, was retrieved from the NGS datasheet database and converted from NAD83 (2011) UTM 18N into WGS84 (G2139) using the HTDP online transformation utility version 3.5.0 (https://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml). The resultant base position used for post-processing was 39°02’21.66695 North (WGS84-G2139), 74°46’08.81537 West (WGS84-G2139), and -34.526 meters (m) ellipsoid height (WGS84-G2139). The kinematic trajectories (rover to base) and base station coordinates were imported and processed using NovAtel’s Waypoint GrafNav software. Each kinematic GNSS data session from the survey vessel was post-processed to the concurrent base GNSS data session. Analyzing the data plots, trajectory maps, processing logs, satellite health plots, and other viewing utilities that GrafNav produces, provided measures to attain trajectory solutions (between the base and the rover) free of erroneous data that resulted in fixed positions. Some examples include 1) excluding satellites flagged by the program as having bad/poor health or cycle slips, 2) Excluding poor satellite time segments that have a negative influence toward a fixed solution, and 3) adjusting the satellite elevation mask angle to improve the position solutions. The final differentially corrected, precise DGPS positions were computed at 0.1 s and exported in American Standard Code for Information Interchange (ASCII) text format in WGS84 (G2139) UTM 18N geodetic datum.

Bathymetry Processing: All data were processed using CARIS HIPS and SIPS (Hydrographic Information Processing System and Sonar Information Processing System) version 11.4.23. First, a vessel file *.vhf unique to the platform, was created that contains the surveyed offsets measurements between the sensors. A CARIS project was created using the *.vhf file, and then the HYPACK .RAW and the SPV profiles *.SVP were loaded. Next, the differentially corrected navigation files were imported using the generic data parser tool. Then, the differently corrected navigation files overwrote every non-differential position in the HYPACK .RAW file based upon time. The bathymetric data components (position, motion, depth, and SOS) were then georeferenced and geometrically corrected in CARIS to produce processed x,y,z positional data. Once georeferenced, the data were reviewed and edited for outliers, including further review in the Subset Editor utility for crossing status, and questionable areas or data points were removed. The geometrically corrected point data were then exported as an x,y,z ASCII text file referenced to WGS84 (G2139) UTM 18N.

Quality Control, Quality Assurance (QA/QC) and Uncertainty Analysis: The single-beam data exported from CARIS HIPS and SIPS (x,y,z ASCII text file) were transformed in Esri ArcMap version 10.8.2.28388 to a point shapefile (.shp) utilizing the "Create Feature Class From XY Table" geoprocessing tool. The projection was set to WGS84 UTM 18N. The generated shapefile was visually scanned for any obvious outliers or problems. Next, a polyline shapefile (representing tracklines) was produced from the point shapefile using XTools Pro (version 22.0.4481) "Make Polylines from Points" geoprocessing tool for each survey platform (subFANs 22BIM03 and 22BIM05). Utilizing both the x,y,z (point) and trackline (polyline) shapefiles, a Python script was used to evaluate elevation differences at the intersection of crossing tracklines by calculating the elevation difference between points at each intersection using an inverse distance weighting equation with a search radius of 5 m. The root mean square (RMS) error for SLED (22BIM05), when crossing a trackline it previously surveyed, was 5.60 cm. The RMS error for WVR2 (22BIM03), when crossing a trackline it previously surveyed, was 4.65 cm. Once individual platform statistics were obtained, both datasets were merged into one file, and the crossing analysis yielded a 5.32 cm RMS error. These files were then exported from Esri ArcMap as x,y,z ASCII text (.txt) files using the XTools Pro "Table to Text" function. The resultant ASCII text file can be downloaded from this data release (Lyons and others, 2023) in Seven_Mile_Island_2022_SBES_WGS84_UTM18N_xyz.zip, and the trackline shapefile from Seven_Mile_Island_2022_SBES_WGS84_UTM18N_tracklines.zip.

Datum Transformation: NOAA/NGS's VDatum v.4.1 was used to transform the single-beam data points' horizontal and vertical datums (x,y,z). The first transformation was from WGS84 (G2139) UTM 18N into NAD83 (horizontal) UTM 18N and NAVD88 (vertical) using GEOID18. The second transformation was from WGS84 (G2139) UTM 18N into NAD83 UTM 18N and NAVD88 using GEOID12B. VDatum reports a nationwide standard deviation of 2.0 centimeters (cm) for ellipsoid - NAD83 transformations, and a nationwide standard deviation of 5.0 cm for NAD83 to NAVD88 transformations in the coastal regions of the continental U.S. For more information about the positional accuracy for these datum transformations, visit the Estimation of Vertical Uncertainties VDatum webpage, https://vdatum.noaa.gov/docs/est_uncertainties.html. The resultant ASCII text data files can be downloaded from this data release (Lyons and others, 2023) in Seven_Mile_Island_2022_SBES_NAD83_NAVD88_UTM18N_GEOID18_xyz.zip and Seven_Mile_Island_2022_SBES_NAD83_NAVD88_UTM18N_GEOID12B_xyz.zip.