Processed high-resolution gridded multibeam bathymetry data from the New England Mud Patch

These multibeam bathymetry grids were collected in 2015 aboard the R/V Sharp, as part of the Office of Naval Research-sponsored Seabed Characterization Experiment (https://wwwext.arlut.utexas.edu/sbcex/). The rectangular survey region, oriented ~E-W in ~60-80 m water depths, measured ~11 km wide and 30 km long. It included 42 strike (E-W) lines spaced ~250 m apart that were used to form the data grids. Multibeam data were collected using a Reson 7125 instrument operating at 200 kHz, and processed using CARIS software. Differential GPS were used for navigation, and an Applanix POS MV inertial motion unit provided attitude control. Raw bathymetry were corrected for pitch, heave, yaw and roll. Raw bathymetry are also manually edited to remove erroneous echosounder pings, recognizable by large positive or negative anomalies from the norm. Conductivity-temperature-depth (CTD) casts were periodically collected and used to determine water depths from the swath soundings. However, this processing step posed a difficult challenge owing to the rapidly changing water masses in the survey region, which was influenced by eddies from the nearby Gulf Stream; CTD readings were insufficiently sampled both in time and space to adequately characterize the variability of the sound speed profile. Incorrect assumptions about sounds speed profile cause the cross-swath profile to either curve upwards (“smile” artifacts) or downward (“frown” artifacts). These effects can be empirically corrected within CARIS, but result in added uncertainty in the overall depth which are often expressed as mismatch between adjacent swaths. The data files are in NetCDF format (suitable for importing to GMT scripts), gridded at 1m to enhance visualization of small-scale features, which are numerous. Projection is in UTM Zone 19N. To keep file sizes manageable, the data grids are sectioned into eastern, central and western subregions.