GeoTIFF image of interferometric backscatter data collected by the USGS within Red Brook Harbor, MA, 2009 (RB_Backscatter_1m)

Bathymetric and backscatter data were collected using a Systems Engineering and Assessment, Ltd. SWATHplus (234 kHz) interferometric sonar system. The SWATHplus transducers were mounted on a rigid pole, approximately 0.5 m below the water line, from the bow of the of the R/V Rafael of Woods Hole, MA. A CodaOctopus F-180 Attitude and Positioning System, mounted directly above the SWATHplus transducers, measured vertical displacement (heave) and attitude (pitch and roll) of the vessel during data acquisition. An Applied Microsystems Ltd. Micro SV sound velocimeter, mounted adjacent to the SWATHplus transducers, continually measured changes in sound-velocity near the sea surface, and a hand-casted, Applied MicroSystems SV Plus sound velocimeter was used to collect sound-velocity profiles of the entire water column at least once each survey day. SWATHplus acquisition software was used to control the transducers and digitally log sonar data across an 80 m swath in SWATHplus raw (SXR) format. To obtain 100 percent coverage of the seafloor, survey lines were spaced approximately 30 m apart. The R/V Rafael maintained an average speed of 5 knots during survey operations. An empirical gain normalization was applied to backscatter data to optimize the dynamic range of recorded intensities, and data was interpolated across gaps at nadir that resulted from the filtering methods applied to the bathymetric soundings.