5-meter per pixel acoustic backscatter mosaic collected by the U.S. Geological Survey offshore of Fire Island, NY in 2011 (FI_SONAR_5M, UTM Zone 18N, WGS 84, GeoTIFF)

Survey: Survey lines were run at an average speed of 5 knots. Lines 1 through 27 were run at a 75-m line spacing to achieve full coverage of the seafloor in a priority area of interest in the nearshore, in water depths less than 15 meters. Lines 28 through 109 were run at a 150-m line spacing, with the exception of tie lines (lines 52 through 60, 65 through 67, 89 through 92), which were run at approximately a 2-km line spacing. Sonar: Swath-bathymetric and acoustic-backscatter data were acquired with a SEA, Ltd., SWATHplus-M interferometric sonar operating at a frequency of 234 kHz and a variable range (increased or decreased manually depending on water depth). The system was operated with a transmit power: 80 percent, 4096 samples per channel, and a variable range (increased or decreased depending on water depth). The SWATHplus-M was mounted on the port side of the M/V Scarlett Isabella during survey operations. A Coda Octopus F180R Attitude and Positioning system recorded ship motion (heave, pitch, roll, and yaw). These data were transmitted via network connection to the SWATHplus-M acquisition software. The Octopus F180R Inertial Measurement Unit (IMU) was mounted directly above the SEA SWATHplus-M transducers, to minimize lever arm offsets that can lead to positioning errors. The F180R uses two L1 antennas for position and heading accuracy. The antennas are mounted on a rigid horizontal pole, positioned at the top of the sidemount, with a horizontal separation of 1 meter and are offset from the IMU in a forward/aft configuration. The forward offset of the primary antenna from the IMU is 0.5 meters, with no port/starboard offset. Sound Velocity Profiles: 135 sound velocity profiles were acquired during survey operations at roughly 1 to 3 hour intervals using an Odim MVP30 motion vessel profiler. The MVP30 failed during survey operations. Sound velocity profiles were only collected during JD140 through 149 (lines 1 through 47). While much effort was devoted to cleaning the data and minimizing survey artifacts, some artifacts may still be seen in the final GeoTIFF including an along track artifact at nadir (the ship track). These artifacts are especially noticeable in the shallow nearshore region of the survey. More information about this field activity and the data collected can be found at the Field Activity Web Page (http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2011-005-FA)