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/>
Field activities 2009-002-FA and 2010-004-FA: Navigation was acquired with a Coda Octopus F180 Differential Global Positioning System + Wide Area Augmentation System (DGPS+WAAS); which are accurate to + or - 1 to 2 meters, horizontally. All DGPS data are referenced to WGS84. The SWATHPlus transducers were mounted on a rigid pole, approximately 2.46 m below the water line, along the starboard side of the M/V Megan T. Miller. The DGPS antenna was located on the same pole approximately 4.3m above the sea surface. These offsets were corrected within the SWATHPlus acquisition software.
Field activity 2011-004-FA: Navigation was acquired with a Coda Octopus F180 Differential Global Positioning System + Wide Area Augmentation System (DGPS+WAAS); which are accurate to + or - 1 to 2 meters, horizontally. All DGPS data are referenced to WGS84. The SWATHPlus transducers were mounted on a rigid pole, approximately 2.17 m below the water line, along the starboard side of the M/V Scarlett Isabella. The DGPS antenna was located on the same pole approximately 4.6m above the sea surface. These offsets were corrected within the SWATHPlus acquisition software.
The DGPS horizontal positional accuracy is estimated to be within 3-5 m; WAAS enable DGPS accuracy is estimated to be within less than 3 m and the accuracy of RTK-GPS (which was not applied to the horizontal positions for these surveys) is estimated to be less than 1 m. However, the U.S. Coast Guard maintains a maritime DGPS service providing 10 meter accuracy for the coastal areas of the continental US; therefore, a very conservative, worse-case estimate of the horizontal positional accuracy of this survey data is approximately 10 meters (although these systems have been shown to be reliable to less than 2m). (sources: <http://www.noaa.gov>; <http://www.nos.noaa.gov>; <http://www.ngs.noaa.gov>; <http://www.nstb.tc.faa.gov/>; <http://www.navcen.uscg.gov>).
USGS field activities 2009-002-FA, 2010-004-FA and 2011-004-FA: Vertical accuracy of the raw data based on system specifications may approximate 1% of water depth, 0.10.4 meters within the survey area. However, overall vertical accuracies on the order of 50cm or more are assumed based on the following considerations: The Coda Octopus F180 Attitude and Positioning system was used to correct for vessel roll, pitch, heave, and yaw, which has a theoretical vertical accuracy of a few mm. Tidal offsets were corrected to MLLW using Real-Time Kinematic GPS (RTK-GPS) heights in post-processing (see process steps). Corrections were sent via cellular modem and VHF radio to the ship from the base station on land. The primary reference station is located at the USGS Marine Operations Facility (MOF) in Falmouth, MA. Field tests using submerged targets suggest that the vertical accuracy of the RTK-GPS tidal correction is less than 30cm. Refraction artifacts were minimized by acquiring a range of sound velocity profiles with a hand-casted Applied MicroSystems SV Plus sound velocimeter during survey 2009-002-FA and an ODIM MVP30 moving vessel profiler during surveys 2010-004-FA and 2011-004-FA. Sound velocity data are entered into the SWATHPlus acquisition software to model the sound velocity structure of the water column. Gridding algorithms and cell sizes for these data could introduce errors as great as 3m along the edges of the data, but gridding-induced errors are likely much smaller (less than 20cm) for most of the survey area. Changes in ship draft due to water and fuel usage were not considered.