More information about the individual USGS surveys conducted as part of the Vineyard Sound project can be found on the Woods Hole Coastal and Marine Science Center Field Activity webpage:
2009-002-FA: <http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2009-002-FA>
2010-004-FA: <http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2010-004-FA>
2011-004-FA: <http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2011-004-FA>
Field activity 2010-004-FA: The Klein 3000 was towed from the stern A-frame of the M/V Megan T. Miller. Real-Time Kinematic (RTK) GPS position data were provided by the Novatel DL-V3 receiver and recorded to the raw data files (XTF) via SonarPro (version 11.0) on the sonar acquisition computer. The GPS antenna was mounted on the top of the SWATHplus (interferometric bathymetry) transducer pole, midship on the starboard side (the middle of the 3 bathymetry system antennas). On a few brief occasions the RTK-GPS signal was lost and the navigation system fell back to standalone DGPS or GPS mode. In these cases, the lower quality positions were used and no corrections were made for RTK navigation gaps. All GPS data during this survey were referenced to the WGS84 horizontal datum. The horizontal offsets between the GPS antenna and the sheave on the A-frame were measured prior to the survey (x:-4.1m; y:-14.94m; z:-1.33m). Additional layback position, accounting for the linear distance between the sheave on the A-frame and the towed sonar system were measured by a 3PS digital block cable counter on the winch that was used to deploy the sidescan-sonar towfish. All of the horizontal offsets were directly applied into the acquisition software so the navigation recorded in the XTF data reflect the position including the layback offset. The layback calculations do not account for fish motion behind the vessel, which is caused by sea state and vessel speed induced changes in the angle and scope of the tow cable. RTK positional accuracy is estimated to be within less than 1 m. Taking the additional fish motion, cable movement and RTK-GPS navigation dropouts into account, a conservative estimate of positional accuracy for this dataset is estimated to be within 10 m.
Field activity 2011-004-FA: The Klein 3000 was towed from the stern A-frame of the M/V Scarlett Isabella. Differential GPS (DGPS) position data were provided by the Ashtech BRG2 receiver and recorded to the raw data files (XTF) via SonarPro (version 11.0) on the sonar acquisition computer. The GPS antenna was mounted on the forward end of the acquisition lab van. All GPS data during this survey was referenced to the WGS84 horizontal datum. The horizontal offsets between the GPS antenna and the sheave on the A-frame were measured prior to the survey (x: +4.31m; y:-9.18m; z:0.0m). Additional layback position, accounting for the linear distance between the sheave on the A-frame and the towed sonar system were measured by a 3PS digital block cable counter on the winch that was used to deploy the sidescan-sonar towfish. All of the horizontal offsets were directly applied into the acquisition software so the navigation recorded in the XTF data reflect the position including the layback offset. The layback calculations do not account for fish motion behind the vessel, which is caused by sea state and vessel speed induced changes in the angle and scope of the tow cable. DGPS positional accuracy is estimated to be within 3-5 m; WAAS enable DGPS is estimated to be within less than 3 m. Taking the additional fish motion and cable movement into account, a conservative estimate of positional accuracy for this dataset is estimated to be within 10 m.
Setup Option: Navigation= Lat/Lon Navigation Interval= 1 minute
Demultiplexing Range and Filter Options: Across track=4 (pixels) Along track= 3 (pixels) Port/Starboard Normalize = 4095 Port High Pass: 65535 Input= 16 bit Normalize Image= yes.
During the demux step, a digital number value of 10 was used as the altitude Search Strength (DN) for the first bottom return. After demultiplexing, each line file (*.d) was reviewed using ShowImage (ver. 1.0) to ensure that the bottom picks were correct and a new bottom was digitized if required.
Next, each file was merged with the navigation created in the demux step and corrected for slant range (*.ds) and beam pattern corrections using the following parameters:
Number of lines= 150 Ping overlap=45 Max beam angle= 90 Response angle=55 Data normalization (0-255)=1 Port/Stbd Tone Adjustment= "on" and "Normal"
The navigation for the final line file (*.dsb) was reviewed using the "Navigation" option in the main Xsonar window. Duplicate points are deleted and navigation is remerged into the ds file if required.
The final step in Xsonar produces separate raster files at 1.0 meter resolution in UTM Zone 19 coordinates for even and odd line files Mosaic boundaries were defined within the survey trackline planning scheme such that the sonar images mapped in XSonar would have the same line orientation and keep the working mosaics to a manageable file size.