Generating Bathymetric Grid: University of New Brunswick, Ocean Mapping Group (OMG) SwathEd Multibeam Processing Software (Beaudoin, 2002)
1) Bathymetric data (raw SXR files), sound velocity profiles, and system configuration information (antenna offsets, transducer offsets, water level, attitude and positioning) were used to generate a composite bathymetric grid using the University of New Brunswick's Ocean Mapping Group (OMG) SwathEd multibeam processing software. The raw Submetrix 2000 Series data were "unraveled" and reformatted into the OMG format. This process creates several files on disk:
a) bathymetric soundings (*.merged) b) raw backscatter (*.ss) c) navigation (*.ascii_nav and *.nav) d) parameter files describing the configuration of the system (i.e. offsets between motion reference unit and GPS antenna, etc.). This process also incorporates the sound velocity profiles in order to properly account for any refraction due to fluctuations in the speed of sound within the water column. (All data were processed, however only lines 43 - 112 were used to generate the bathymetric grid).
2) The OMG formatted bathymetric data (*.merged) were then graphically edited on a line-by-line basis using the SwathEd multibeam processing software. This enabled editing individual lines on a "ping-by-ping" basis, both in the across- and along-track dimension. Spurious or erroneous data were removed. The navigation data (*.nav) were also graphically examined for each line of data.
3) SwathEd Software was used to grid the bathymetric data at 1 m grid cell size utilizing the following 'weigh_grid' command.
weigh_grid -omg -butter -power 2 -cutoff 2 -lambda 0.5 bathy_grid *.merged
4) The gridded data were then viewed using the SwathEd Jview command in order to assess roll misalignment and any remaining navigational errors. The PatchTool (a Quality Control tool) was used to assess the roll misalignment of the data that can arise due to the minor offsets in the nominal transducer angles entered in the configuration file and used during data processing. After editing was completed, the corrected roll values and navigation were remerged with the OMG-formatted bathymetric data (*.merged) using the mergeNav and mergeAtt commands.
mergeNav -use_params 0 -nav *.nav -swath *.merged)
5) The remerged data were regridded to assess if further edits were needed.
weigh_grid -omg -butter -power 2 -cutoff 2 -lambda 0.5 bathy_grid *.merged
The roll misalignment artifacts were no longer visible in the gridded data and spurious navigation positions were removed.
6) The 1 meter grid was then exported to an xyz ASCII file format.
(r4toASCII -utm -merid -69 bathy_1m.xyz)