More information about the individual USGS surveys conducted as part of the Buzzards Bay project can be found on WHCS Field Activity Web pages:
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>
Information about the NOAA survey can be found at:
H11319: <http://surveys.ngdc.noaa.gov/mgg/NOS/coast/H10001-H12000/H11319/DR/>
This shapefile includes trackline navigation from all the sidescan sonar data that was collected within the survey area; however only quality sonar data along the main survey lines were included in the sidescan sonar mosaic that is found on this report (BB_backscatter1m.tif). Noisy or poor quality data were not mosaicked. Data were omitted where it overlapped with equal or better quality data from an adjacent survey line (as was generally the case for lines less than several hundred meters long). Data from parts of lines l130f2_090606081500 and l131f1_090606091400 were omitted as they extended beyond the extent of the survey area and into an area covered by a previous sidescan sonar survey (<http://pubs.usgs.gov/of/2006/1357/>).
Some of the raw (.XTF) files for the sidescan-sonar survey lines were originally named without an underscore between the concise linename and the SonarPro generated timestamp part of the filename. Before processing the navigation files, all XSonar generated navigation files (.nav) were made consistent to have the underscore (e.g. l1f1090528041200.nav became l1f1_090528041200.nav).
Field activity 2010-004: 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). The side-scan tow cable was deployed through a 3PS digital block cable counter attached to the A-frame. Real-time cable-out measurements were transmitted via serial connection to the SonarPro acquisition software, which calculated tow-fish layback. All horizontal offsets were directly applied in 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 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: 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). The side-scan tow cable was deployed through a 3PS digital block cable counter attached to the A-frame. Real-time cable-out measurements were transmitted via serial connection to the SonarPro acquisition software, which calculated tow-fish layback. All horizontal offsets were directly applied in 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 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.
2009-002-FA SonarPro version: 10.0 nav: from the antenna on the aft end of the acquisition van into the Ashtech BRG2 receiver (DGPS) sheave offsets x: -2.0m; y: -8.35m; z: +2.0m
2010-004-FA SonarPro version 11.0 nav: from the center antenna on the SWATHplus pole into the NovAtel DL-V3 receiver (RTK) sheave offsets x: -4.1m; y: -14.94m; z: -1.33m
2011-004-FA SonarPro version 11.0 nav: from the antenna on the fwd end of the acquisition van into the Ashtech BRG2 receiver (DGPS) sheave offsets x: +4.31m; y: -9.18m; z: 0.0m