Coastal Single-Beam Bathymetry Data Collected in 2025 From Midnight Pass, Florida

GNSS Acquisition: As reported on the FPRN FLSC CORS station datasheet, the base station was equipped with a Leica Geosystems® GR50 GNSS receiver using a Leiar20 SCIT antenna recording at a rate of 1.0 seconds (s) equal to 1 hertz (Hz). The roving vessels were each equipped with a Spectra Precision® SP90M GNSS receiver using Spectra Precision® SPGA Rover GNSS antennae recording full-carrier-phase positioning signals from satellites at a rate of 0.1 s, or 10 Hz. Post-survey, the base station data files were downloaded from the FDOT FPRN online server location in the non-proprietary Receiver Independent Exchange Format (RINEX [https://igs.org/wg/Rinex/]) format version 3.04 (e.g. FLSC17600.250). The proprietary Spectra Precision G-files (e.g. GWVR1A24.176) from the rovers were converted into RINEX format version 3.04 (e.g. WVR100000_R_20251762001_02H_10Z_MO) which converts all the satellite constellations tracked by the antenna (GPS, GLONASS, BeiDou, and Galileo). Example of the RINEX 3.04 filename is FLSC176l00.25O, where the convention FLSC is the four-letter site name, 176 is the day of year, I is the session A-Z, 00 is the time, 25 is the year, O represents the observation file, N is the navigation file, M is meteorological file, and G is the GLONASS navigation message file. Example of the RINEX 3.04 filename WVR100000_R_20251762001_02H_10Z_MO where the convention WVR100000 is the nine-letter site name, R is the data source (R - receiver), 20251762001 is the year (2025), day of year (176), and Coordinated Universal Time (UTC) start time of the file in HHMM (2001), 02H is the file time (2 hours), and the 10Z is the recording rate (10 Hz), MO is the mixed observation file, MN is the mixed navigation file, and MM is meteorological file.

Single-Beam Bathymetry Acquisition: A total of 47 line-km of SBES data were collected as part of FAN 2025-313-FA: the R/V Shark (WVR1 - subFAN 25BIM03) collected 24 line-km, and R/V Chum (WVR2 - subFAN 25BIM04) collected 23 line-km of data. Boat motion (heave, roll, pitch) was recorded on each vessel at 50-millisecond (ms) intervals using a SBG Systems Ellipse Series A motion sensor. HYPACK®, a marine surveying, positioning, and navigation software package, managed the planned-transect information and provided real-time navigation parameters, course corrections, data quality parameters, and instrumentation-status to the boat operator. Depth soundings were recorded at 50-ms intervals using a Teledyne® Odom Echotrac CV100 echosounder with a 4-degree, 200-kilohertz (kHz) transducer on WVR1 and WVR2. For each vessel, data from the GNSS receiver, motion sensor, and echosounder were recorded in real-time 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 UTC. Sound velocity profile (SVP) measurements were collected using SonTek® Castaway Conductivity, Temperature, and Depth (CTD) instruments. The CTD units were cast overboard to record changes in water column speed of sound (SOS) spatially and temporally. A total of 6 casts recorded sound velocities ranging from 1546.45 to 1550.33 meters per second (m/s) at water depths ranging from a minimum of -0.15 m to a maximum of -5.55 m.

Differentially Corrected Navigation Processing: All navigation data were acquired in WGS84 (G2296)/International Terrestrial Reference Frame of 2020 (ITRF2020). The FLSS coordinates used for post-processing the navigation collected during this survey were 27° 13' 02.19597" North, 82° 24' 17.10539" West, -16.907 m ellipsoid height, and epoch 2025.0073 obtained from the FPRN FLSC datasheet (https://www.myfloridagps.com/ds/pdfs/flsc.pdf). The rover data, base data, and the base station coordinates were imported into GrafNav (NovAtel, 2023). Each kinematic GNSS data session from the survey vessel was post-processed to the concurrent static base GNSS data session. GNSS data plots and data information generated by GrafNav including satellite health (satellite lock, satellite cycle slips), rover trajectory maps, and pre-processing logs were used to modify the processing parameters to attain trajectory solutions (between the base and the rover) that resulted in fixed positions. Primary examples include: 1) excluding satellites, flagged by GrafNav, with bad health or frequent cycle slips, 2) omitting satellite time segments that introduce positional errors which prevented a fixed solution, or 3) adjusting the satellite elevation mask angle to improve the position solutions (NovAtel, 2023). The final differentially corrected, precise DGPS positions were computed at 0.1s and exported as a single data point epochs in ASCII text format (.txt) in WGS84 (G2296) UTM Zone 17N geodetic datum.

Single-beam Bathymetry Processing: All data were processed using HYPACK® 2023 following steps outlined in the HYPACK® 2023 User Manual (Xylem, 2023). First, the HYPACK® project geodesy settings were verified, ensuring the correct UTM Zone and "K-N from User" settings with "height of ellipsoid above chart datum" value of '0.00 were selected. Next, the .RAW data files were imported into HYPACK® Single Beam Editor (64 bit). The following "Read Parameters" were selected within the Survey Tab 'Elevation Mode' and the project information was verified. Within the Corrections Tab: the sound velocity profiles (SVP) were added as .VEL format, and 'Time and Position' was selected for the SVP interpolation method. Within the Devices Tab: the vessel offsets were added and the RTK Tides box was selected. Within the Processing Tab: 'Apply Heave Correction', 'Correct Induced Heave', 'Remove Heave Drift', 'Avoid Double Heave', 'Merge Tide Data with Heave', 'Interpolate Draft', 'Apply Pitch and Roll Corrections', and 'Steer Sounding Beam' (4 degree for the WVR1, and WVR2) were all selected. The data was then processed within HYPACK®'s Single Beam Editor (64 bit). Next, the GPS Adjustment tool was used to merge the post-processed navigation trajectory epoch solutions with their respective HYPACK® data files (.RAW). Using the Editor Profile window, these processed soundings were visually scanned for any resultant outliers which were manually removed using the editor tool. The data were then smoothed using the smoothing option with the 'number of samples for average" set to 60. Finally, the x,y,z data (easting, northing, ellipsoid height) and associated attributes (calendar date, UTC time, and line number) were exported as a single text file per line. The text files were them combined into one file per subFAN/vessel using the ArcGIS Pro's "Merge (Data Management)" geoprocessing tool, resulting in two main text files.

Quality Control, Quality Assurance (QA/QC) and Uncertainty Analysis: Using ArcGIS Pro, the processed single-beam datasets were then transformed into feature classes using the "Create Points From Table > XY Table to Point" geoprocessing tool and the spatial reference was set to WGS84 UTM 17N. Next, a polyline feature class (representing tracklines) was produced from the point data using XTools Pro "Make Polylines from Points" (the selection criteria being HYPACK® line name and then ordering by UTC time). Utilizing both the point and polyline feature classes, an ArcGIS Pro Python script was used to evaluate the elevation differences at the intersections of tracklines. The script does this by calculating the elevation difference between points at each intersection using an inverse distance weighting equation with a search radius of 1 m. The crossing analysis yielded a Root Mean Square Error (RMSE) of 4.00 centimeters (cm) for all crossings. When the WVR1 crossed one of its own lines, the crossing analysis yielded an RMSE of 7.1 cm. When the WVR2 crossed one of its own lines, the crossing analysis yielded an RMSE of 6.4 cm. The crossings in ArcGIS Pro were solely used as a QA/QC, not as a means of editing the data.

Datum Transformation: NOAA NGS's VDatum software was used to transform the single-beam data points' horizontal (x,y) and vertical (z) datums from WGS84 (G2269) UTM 17N (horizontal), WGS84 (G2269) ellipsoid height (vertical) using epoch year 2025.479 (start of the survey) to NAD83 UTM 17N (horizontal), NAVD88 orthometric height (vertical) using GEOID18 epoch year 2010.000. The VDatum-reported vertical uncertainty is 0.032 m. 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.

Digital Elevation Model (DEM) Creation: Using ArcGIS Pro version 3.2.3 and the single-beam point data file (Midnight_Pass_2025_SBES_WGS84_G2296_UTM17N_xyz.txt), a 1 x 1-m cell resolution DEM was generated using ArcGIS geoprocessing tools. First, a polygon feature class was created using "Create Feature Class (Data Management)" tool and was shaped to the single-beam data file extent using ArcGIS Pro "Edit Vertices" tool. This polygon feature class was then converted to a 1 X 1-m cell size raster using the "Feature to Raster (Conversion)" tool. Second, using the single-beam point data file (Midnight_Pass_2025_SBES_WGS84_G2296_UTM17N_xyz.txt), a 1-m DEM was generated using the "Natural Neighbors" (Spatial Analyst) tool. Third, the DEM was clipped to the 1-m raster (created in the first step) using the "Extract by Mask (Spatial Analyst)" tool. The computation results produced minimum and maximum ellipsoid height values of -25.96 to -31.87, which closely resemble the single beam point data values of -25.93 to -31.88. Last, to quantify how closely the 1-m DEM represents the single-beam point data, the "Extract Values to Points (Spatial Analyst)" tool was used. This tool extracts the value from the DEM at each single-beam data point location. The 1-m DEM represented 460,721 of 462,569 data points with 1,848 (0.40%) reported as null values. Using the generated feature class and associated attribute table, the RMSE was calculated as 0.023 m. The DEM was then exported as a Geographic Tag Image File Format (GeoTIFF, .tif) file with the symbology set to stretch.