Processing steps 1 and 2 produced a preliminary bathymetry dataset. Processing to further edit the data, correct for tides, and to produce a final grid of the merged 1996, 1998, and 2000 data included:
1. Correct errors in soundings due to sound refraction, caused by variations in sound velocity profile, using the SwathEd refraction tool. These artifacts can be recognized in a cross-swath profile of a relatively flat patch of sea floor. When viewing the swath data across a profile, the sea floor will appear to have a "frown" or "smile" when in fact the data should be flat across the profile. Insufficient and/or erroneous sound velocity information, which is usually due to widely spaced or non-existent velocity profiles within an area, results in an under or over-estimate of water depth which increases with distance from the center of the swath. For a discussion of how this effect can be recognized in a swath bathymetric data file, see
2. Remove erroneous soundings that were not edited in the field using the SwathEd program.
3. Adjust the measured elevations for tidal fluctuations by subtracting tidal elevations and mean sea level predicted by the ADCIRC tidal model (Westerink and others 1994; Luettich and Westerink, 1995; see cross references). A MATLAB script was used to interpolate the ADCIRC constituents along the ship track and then calculate the tidal elevation and mean sea level at the time of the survey. The vertical datum of the ADCIRC correction is NAVD88.
Using the adjusted tidal elevations, create a binary tide file to be used in merging the tidal heights with the bathymetric soundings.
Command line: binTide -year YYYY asciiTideFile BinaryTideFile
The program mergeTide brings the swath soundings to NAVD88 and corrects for predicted tide.
Command line (tides): mergeTide -tide BinaryTideFile filename.merged
4. Correct near-nadir beams for depth offset caused by error in EEPROM programming for 1996 and 1998 datasets (see Logical Consistency Report)
Command line: deHump -depscale 0.0105 filename.merged
5. Create a final 12-meter grid of the edited bathymetric soundings from each line file (filename.merged) using the SwathEd routine weigh_grid.
Command line: weigh_grid -fresh_start -omg -tide -coeffs -mindep -2 -maxdep -800 -beam_mask -beam_weight -custom_weight EM1000_Weights -butter -power 2 -cutoff 24 -lambda 6 gridFile filename.merged
Note: Errors in the UNB gridding software were identified in 2003 and 2007. These data were processed with corrected software.