Multibeam Bathymetry Data Collected in 2019 from Grand Bay and Point Aux Chenes Bay Alabama/Mississippi: Processed Elevation Point Data (x,y,z)

Acquisition: An ERS was conducted using a Teledyne Reson SeaBat T50-P multibeam echosounder. The multibeam transducer and receiver (standard bracket configuration, horizontally tilted 62.5 degrees to port as well as a flat configuration) were attached to a pole mount deployed over the port side gunnel of the R/V Jabba Jaw, a 22-ft fiberglass shallow draft center console catamaran. An Applanix POS MV Wavemaster II V5 inertially aided navigation system was used for timing, positioning, and attitude. The Inertial Measurement Unit (IMU) was mounted to a bracket attached to the pole, above the sonar bracket. Two Trimble GA830 Global Navigation Satellite System antennas were affixed to the top of the sonar mount pole, one meter apart, fore-aft. An AML Oceanographic Micro-X sound velocity sensor was used for speed of sound readings at the sonar head. A Sontek Castaway-CTD was used for measuring sound velocity profiles. Hydrographic survey acquisition and processing software, HYPACK/HYSWEEP (version 2018a) managed planned line and data inputs from sensors and produced two files (.RAW and .HSX). Data were collected in WGS84 [G1762] Universal Transverse Mercator (UTM) Zone 16 North (16N) coordinates.

Processing: Positioning and attitude data were post-processed in Applanix POSPac MMS (POSPac) software version 8.0 Service Pack 3. Raw position files 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 (SMRMSG) for each day of the survey. Bathymetric data were post-processed in CARIS Hydrographic processing software HIPS/SIPS version 11.3. HYPACK acquisition files (.HSX) were first imported into CARIS and then post-processed navigation files (SBET and SMRMSG) were imported and applied. Additionally, GPS tide (GPS tidal corrections utilize GPS height information from real time survey observations to obtain an ellipsoid height) was computed and sound velocity profiles were applied. Roll calibration was also performed, as necessary. TPU was calculated from real time values recorded in the HSX and the SMRMSG files. Data were filtered to exclude any points with RESON Quality flags of 0, 1, and 2 these flags are assigned to individual soundings at the time of acquisition and are a metric of pass/fail in regards to both brightness and collinearity: 0 = fail both, 1 = pass brightness only, 2 = pass collinearity only), as well as soundings that had a TPU greater than stated IHO Special Order standards (IHO, 2008). Refraction artifacts were addressed using Refraction Editor. Further editing was performed in Subset Editor. A visual and statistical inspection of the data was performed to serve as quality control. A 1-m bathymetric CUBE surface was computed utilizing data specific to sonar head configuration and the final surfaces were exported as an x,y,z ASCII file using the Base Surface to ASCII function.

Datum Transformation: Final x,y,z data were converted using NOAA’s VDatum software conversion tool v.4.0.1 (reported vertical transformation error is 7.6158 centimeters [cm]) from the WGS84 (G1762) realization with elevation data provided in ellipsoid height to NAD83 (2011) NAVD88, using the GEOID12A model (orthometric height).

Added keywords section with USGS persistent identifier as theme keyword.