XSonar/ShowImage sidescan-sonar processing software was used to process the raw XTF sonar data following the methodology of Danforth, (1997). A 4 across track x 3 along track pixel median filter was applied to the raw sidescan-sonar data to remove speckle noise and a normalization of 4095 was applied to adjust the dynamic range within the output processed file. Processed data are stored as 8-bit. Navigation were also extracted from the raw data at 2-minute intervals and saved in an ASCII file. Quality checks were conducted on the navigation to eliminate spurious or duplicate navigation fixes. The sonar data were further processed to correct for towfish altitude (i.e. proper tracking of the lakefloor), and slant-range and beam pattern distortions inherent in the sonar data. Processed sonar files were then merged with the edited navigation. Processed sonar files were then mapped at a 1-meter resolution in UTM coordinates (UTM, Zone 19N, WGS 84, meters) and saved in two XSonar/ShowImage mosaic files representing odd and even (i.e. every other line) sonar tracklines, or files.
Below are the typical parameters for processing with XSonar: File Type: XTF, Low Frequency (132 kHz)
Setup Option: Navigation= Lat/Lon, Navigation Interval= 2 minute
Demultiplexing Range and Filter options: Across track=4 (pixels), Along track= 3 (pixels), Port/Starboard Normalize = 4095 (default), Port High Pass: 65535 (default,) Input= 16 bit, Normalize Image= yes.
Beam Pattern Correction options: Number of lines= 100, Ping overlap=50, Max beam angle= 90 (default), Response angle=55 (default), Data normalization (0-255)=1 (default), Port/Stbd Tone Adjustment= "on" and "Normal"
Jane F. Denny performed this and all subsequent process steps.