Bathymetry of the Hudson Shelf Valley (12-m resolution Esri binary grid and 32-bit GeoTIFF, Mercator, WGS 84)

Data processing and editing at sea
Processing of the data was carried out by USGS personnel with assistance from the Ocean Mapping Group at the University of New Brunswick (UNB), Canada. A suite of processing software (called SwathEd) developed by the Ocean Mapping Group (<Clarke, 1998; see cross reference>) was used to process, edit, and archive the bathymetric soundings. These routines are designed to be run on a Unix and/or Linux operating system.
The processing and editing steps carried out on board the ship were:
1. Demultiplex (unravel) the Simrad data files using RT to generate separate files for a given raw file (filename.raw_all) containing navigation (filename.nav), depth soundings (filename.merged), sidescan sonar backscatter values (filename.merged_ssdata), acquisition parameters (filename.param) sound velocity at the transducer (filename.sv_tdcr) and sound velocity profiler information (filename.svp).
Command line: RT -packdown -background -WRITE -em1000 -CnC -prefix RawFiles/ -suffix _raw.all -out ProcessedFiles/InputFilenamePrefix InputFilenamePrefix
2. Edit the navigation data on-screen using the SwathEd routine jview to remove undesirable points, including turns at the ends of survey lines. Jview also rejects stray GPS fixes outside of the survey area, as set by the operator.
Command line: jview -rejectnav -navedit filename.nav
3. Make a copy of the edited navigation, and then create a new navigation file that has the bad fixes deleted from it.
Command line: mv filename.nav filename.nav_all Command line: appendNav -goodonly -comp filename.nav filename.nav_all
4. Merge the edited navigation back into the file containing the depth soundings using just the prefix of the filename. The location of the antenna relative to the motion reference unit is also entered here, along with a maximum time gap (in seconds) allowed between navigation fixes.
Command line: mergeNav -ahead 5.379 -right 3.851 -below 4.244 -time_limit 300 filename
5. Edit the multibeam soundings for each trackline. SwathEd displays blocks of data across and along the trackline. Anomalous points were identified by comparison to other points and by an understanding of the sea floor geology and morphology. Anomalous soundings were removed.
Command line: SwathEd filename.merged
This methodology was followed in all years of data acquisition: 1996, 1998, and 2000

Map the bathymetric soundings from each processed data file onto a digital terrain model (DTM) in the Mercator projection using weigh_grid with grid nodes spaced at 12 meters. The weigh_grid program creates a DTM by summing up the weighted contributions of all the provided data into the DTM. The weighted contributions only extend to a user defined region around the true location of the estimate (the cutoff). The weight of an individual point contribution decays away from the node location based on the order of the Butterworth (inverse weighting) filter (-power n), the width of the flat topped radius of the weighting function (-lambda n.n), and the absolute cutoff limit (-cutoff) that will be used for data points contributing to a node. In addition, each beam/other value can be pre-weighted if required to account for its reliability. A custom weight file for each beam is created by hand and input into the weigh_grid program using the -custom_weight option. Three files are created which are used by the weigh_grid program. An ".r4" file, which contains the grid node values in binary format, an "r4_weights" file, and an "r4_weight_depth" file. To do the summing of the weights, the .r4_weights file contains the sums of the weights for each data point contributing to the node, and the .r4_weight_depth file contains the sum of the weights x the depths. The solution is: weight_depth/weights for each node. For more information, visit the OMG website at <http://www.omg.unb.ca>.
First a blank binary grid and the weights and weight_depth files must be created:
Command line: make_blank -float gridFile
This command commences a dialog to enable an 8-bit image and input the map boundaries and resolution. The program also prompts for the projection type and parameters to be used creating the binary map file (custom Mercator projection, central longitude of -75 degrees, latitude of true scale 40 degrees north).
The next command creates the weights and weight_depth files associated with the binary grid: Command line: tor4 gridFile
These two steps create all three files with a gridFile prefix.
Next, each individual data file (.merged suffix) is added to the grid using weigh_grid. The grid of Hudson Shelf Valle data were created with a grid node spacing of 12 meters, a cutoff radius of 24 meters, and an inner radius to the weighting function of 6 meters:
Command line: weigh_grid -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

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 < http://www.omg.unb.ca/AAAS/UNB_Seafloor_Mapping.html>.
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.

Convert binary bathymetric grid to Esri ASCII raster format:
Command line: r4toASCII gridFile.r4
This creates a file called gridFile.asc.
Creation of Esri grid
An Esri bathymetry grid was created by importing data from Esri ASCII raster format into Esri grid format.

The SwathEd processing software produced depth as positive values. Change depth from positive to negative using the Negate function in ArcToolbox - Spatial Analyst Tools - Math - Trigonometric (ArcGIS 9.3).

ArcGIS 10.3.1 was used to export the grid to a 32-bit TIFF image. The extent and spatial reference were set to the original dataset, as was the cell size. The compression type was set to LZW. The NoData value is the default -3.40282306074e+38. The process also creates the TIFF world file automatically.

Added keywords section with USGS persistent identifier as theme keyword.