Santa_Rosa_Island_2021_SBES_xyz: Single-Beam Bathymetry Data Collected During USGS Field Activity Number 2021-322-FA Offshore of Santa Rosa Island, Florida

Acquisition: A single-beam bathymetry survey was conducted in June 2021 aboard the R/V Sallenger, a 26-foot (ft) fiberglass research vessel outfitted with an ODOM CV100 echo sounder system with a 200 kilohertz (kHz) transducer for depth, an Applanix POS MV Wavemaster II V5 inertially aided navigation system (IANS) for timing, positioning, and attitude, and a Sontek CastAway Conductivity, Temperature, and Depth (CTD) sensor was used to measure sound velocity profiles. The ODOM echosounder and the Applanix Inertial Measurement Unit (IMU) were mounted in line vertically to a mounting pole on the starboard gunnel. The IMU was mounted above the sonar and was the center of reference point (0.00 mmeters [m]) for all the sensors used in this survey. When the pole was deployed, the instruments were approximately 1-m below the water surface. The topside part of the Applanix POS MV consisted of two Trimble GA830 Global Navigation Satellite System (GNSS) antennas that were affixed atop the cabin approximately amidships of the vessel, two meters apart, port-starboard (secondary antenna and primary antenna respectively for the R/V Sallenger) and all cables ran into their respective topside control boxes within the cabin. HYPACK version 2021.0.2 hydrographic acquisition and processing software managed incoming sensor data. All sensor data strings were referenced with a device identification code, time stamped to Coordinated Universal Time (UTC), and saved into a single raw (.RAW) data file. Sound velocity measurements were collected using Sontek Castaway CTD units to record changes in water column speed of sound (SOS). CTD profiles were collected based on time and space with inclusions for shallow water, deep water, offshore, inshore, and channel areas. Data were collected in WGS84 [G1762] Universal Transverse Mercator (UTM) Zone 16 North (N) coordinates and WGS84 ellipsoid height.

Navigation processing: Positioning and attitude data files from the Applanix POS-MV Wave Master II V5 were post-processed in Applanix POSPac (POSPac) Mobile Mapping Suite (MMS) software version 8.6. Raw position files from the POS MV were imported into POSPac and processed with the IN-Fusion PP-RTX processing mode utilizing Trimble CenterPoint RTX technology, creating smoothed best estimate of trajectory (.sbet) files and dynamic error files (.smrsmg) for each day of the survey. Data file recording was automated and preset to a maximum file size of 12 megabytes (MB) before opening a new file. File extensions for each survey day started with *.000 and incremented sequentially (*.001, *.002) until recording stopped. File naming convention was 2021_154_USB.000 where 2021 is the year, 154 is the Day of Year (DOY), USB is the digital media storage used, and .000 is file extension as previously described.

Single-beam bathymetry processing: Bathymetric data were post-processed in CARIS Hydrographic processing software HIPS/SIPS version 11.3.6. First, a vessel file specific to the R/V Sallenger equipment offsets and equipment specifications was created (*.vhf) in the "Vessel Editor" application. Next, the HYPACK acquisition files (.RAW), the post-processed navigation files (.sbet and . smrmsg), and the sound velocity profiles (.svp) were imported into CARIS. The bathymetric data components (position, motion, depth, and SOS) were geometrically corrected using the "Georeference Bathymetry Tool" to produce processed XYZ data. Additionally, during this process, the Global Positioning System (GPS) tide component (GPS tidal corrections utilize GPS height information from real time survey observations to obtain an ellipsoid height) was computed and were applied to the data. Next, a loosely defined moving average filter was applied line by line to reduce noisy and erroneous data points. A visual and statistical inspection of the data was further performed in the Subset Editor 2-Dimensional (D) and 3-D utility for crossing status agreements and any questionable areas. The dataset was exported as an XYZ American Standard Code for Information Interchange (ASCII) file using the CARIS HIPS and SIPS Data Export HIPS to ASCII function as WGS84 (G1762) UTM Zone 16N and ellipsoid height in meters.

Single-beam bathymetry error analysis: The ASCII file described in the previous step was imported into ArcMap version 10.8.1 and two shapefiles were created. One shapefile was created to display the data points, the second shapefile was created using the XTools Pro "Polylines from Points" ArcScript to display the tracklines. An Esri ArcMap add-in script using an inverse distance weighted equation was written locally, by a USGS staff member to evaluate the elevation differences at the intersection of crossing lines. The script uses the point and trackline shapefiles concurrently and produces another shapefile with the results. If discrepancies were found at a crossing, the source of the discrepancy was identified and, if needed, the line or segment of data points in error was statically adjusted, removed, or reprocessed. This crossing program was reiterated to produce a final numerical assessment of the crossing range for the SBB dataset. Results from 159 crossings report the minimum is 0.00 m, the maximum is 0.13 m, and a standard deviation of 0.02. Crossing values > 0.15 m = 0% and crossing values > 0.10 = 1%.

VDatum version 4.3 transformation: The xyz point dataset was also converted from WGS84_UTM16N into NAD83(2011) and NAVD88 (orthometric height) with respect to GEOID 12A with a vertical uncertainty reported for this transformation of 0.0605876 m. The reported maximum cumulative uncertainty for the Florida - Perdido, Pensacola and Choctawhatchee Bays VDatum region (https://vdatum.noaa.gov/docs/est_uncertainties.html#estTransform) is 8.3 centimeters (cm).