The geophysical mapping utilized a suite of high-resolution instrumentation to map the surficial sediment distribution, depth and sub-surface geology: dual-frequency 100/500 KHz sidescan-sonar system, 234-KHz interferometric sonar, and 500 Hz -12 KHz chirp sub-bottom profiler. The survey was conducted aboard the M/V Megan Miller August 9-13, 2007. The study area covers 35 square kilometers from about 0.2 km to 5-km offshore of the south shore of Martha's Vineyard, and ranges in depth from ~ 5 to 20 meters.
Data files were recorded by SEA software SWATHplus in the SWATHplus SXR format. Data collection parameters are saved into a SWATHplus session file in SEA's sxs format that can be later used for data replay.
Pitch, roll, heading, and heave information were recorded using a Coda Octopus F180R motion reference unit (MRU) (see: <http://www.codaoctopus.com/motion/f180/index.asp>) and transmitted via network connection to the SWATHplus data collection software. The MRU sensor was mounted directly above the SWATHplus transducers, thereby minimizing "lever arm" offsets which can lead to positioning and depth errors in the bathymetric data. The F180R series MRU uses two L1 antennas for position and heading accuracy. These were mounted directly above the MRU with an offset of 6.76 meters. The antennas are mounted on a rigid horizontal pole with a separation of 1 meter and are offset from the MRU in a forward/aft configuration. The forward offset of the primary antenna from the MRU is 0.5 meters, with no port/starboard offset.
Sound Velocity Profiles (SVP): Fourteen sound velocity casts were collected at various intervals during the USGS cruise 07011 using an Applied Microsystems SV Plus v2 instrument (see <http://www.appliedmicrosystems.com/products/productDetails.aspx?id=1> for details). Sound velocity profiles (SVP) were generally collected at the eastern and western ends of the survey area, corresponding to the start and/or end of geophysical line data collection. This procedure was primarily followed to coordinate collection of SVP casts with the beginning or end of trackline. This was acceptable because only small variations in the speed of sound were noted throughout the survey area and negligible refraction artifacts were visible within the swath bathymetric data.
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