Data collected for the mapping cooperative have been released in a series of USGS Open-File Reports<http://woodshole.er.usgs.gov/project-pages/coastal_mass/html/current_map.html>. This spatial dataset is from the Cape Ann and Salisbury Beach Massachusetts project area. They were collected in two separate surveys in 2004 and 2005 and cover approximately 325 square kilometers of the inner continental shelf. High resolution bathymetry and backscatter intensity were collected in 2004 and 2005. Seismic profile data, sediment samples and bottom photography were also collected in 2005.
The zoning parameters SAIC created were: On Portland, ME (8418150) + 8 minutes ratio 0.964 On Boston Light, MA (8444162) +2 minutes ratio 0.972 All bathymetry data collected during the survey were corrected for water level variations using water level files. Water level files for each tide zone were created from downloaded preliminary NOAA tide data using the Survey Analysis and area Based Editor (SABER) Create Water Level Files tool. Water level files contain water level heights that are subtracted algebraically from depths to correct the sounding for tide and water level. These water level files were applied to the multibeam data using the Apply Tides tool within the SABER software.
Comparison of the zoned 6-minute water level heights computed from Boston Light, MA (8444162) to those computed from Portland, ME (8418150) shows an average height difference of 0.009 meters and a standard deviation of 0.042 meters. The maximum and minimum differences were +0.125 meters and -0.078 meters. Because the Portland, ME (8418150) gauge is a NOAA Primary Control Tide Station water level zoned heights from that station were used to correct the soundings.
Sound velocity casts were taken every 2-4 hours with a Brooke Ocean Technology MVP 30 System and Applied Microsystems Smart Sound Velocity Sensor.
A patch test was conducted at the beginning of the survey in order to measure roll angle offsets. Roll angle offsets can have a strong effect on the accuracy of depth measurements. The roll angle offset is the difference between the motion sensor vertical measurement and the nominal mount angle of the transducers. The calculated roll angle offsets were stored within the SABER acquisition software.
Once the data were in Newport and had been extracted to local machines, track lines were created by extracting the sounder position from the multibeam data. The tracks were reviewed to confirm that no errors in navigation existed and that the tracks extended to the outermost bounds of the survey area.
After the application of preliminary tides and interpolated draft, multibeam binned-depth grids were generated. A 5-meter Pure File Magic (PFM) grid was generated and edited in area based mode using MVE. The 5-meter projected PFM allowed multiple line editing which enhances visualization and proves efficient in the MVE process to ensure data quality. If any anomalies were found in the sounding bins, the edited multibeam files were re-examined and re-edited as necessary. When all multibeam files were determined to be satisfactory, the data were binned to a 5-meter and 2-meter cell size, populating the bin with the average of all soundings in the bin and maintaining the position of the center of the bin.
A new CARIS HIPS project (ver 6.1) was created with the projection information set to Universal Transverse Mercator (UTM) Zone 19, WGS84. The Processed GSF files for all main scheme lines were imported to CARIS using the import/conversion wizard A 5 meter Bathymetry and Statistical Error (BASE) surface was built from the line files. All previous edit flags were imported and no further editing was done in CARIS.