XSonar (versions: 1.1 in 2009 and 2.0 in 2010 and 2011) was used to apply a median filter (4 pixels across track by 3 pixels along track) to the raw sidescan-sonar data (XTF) to remove speckle noise. The data were further processed to correct fish altitudes, reduce slant-range and beam-angle distortions, and merge navigation (Danforth, 1997). Adjacent sidescan sonar lines were mapped out separately from XSonar into north-heading and south-heading sonar mosaics at 1 meter/pixel resolution. Sidescan areas were defined within the survey trackline planning scheme such that the sonar images mapped in XSonar would have the same line orientation and keep the working mosaics to a manageable filesize.
Below are the typical parameters for processing with XSonar:
File Type:
XTF, Low Frequency (132 kHz)
Setup Option:
Navigation= Lat/Lon
Navigation Interval= 1 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= 90
Ping overlap=45
Max beam angle= 90 (default)
Response angle=55 (default)
Data normalization (0-255)=1 (default)
Port/Stbd Tone Adjustment= "on" and "Normal"
Processing occurred in 2009, 2010, and 2011.