Phase 1B Underwater Archaeological Report for the Onondaga ...

FINAL
Phase IB Underwater Archaeological Resources Report for Onondaga Lake Superfund Site
Figure 24. EdgeTech 4125-D sonar towfish (LCMM Collection).
Figure 25. EdgeTech sonar towfish being deployed from the bow of RV Lophius (LCMM Collection).
Sonar data were processed using Chesapeake Technology, Inc.’s SonarWiz software to map the locations
and dimensions of objects on the bottom and to merge adjacent sonar files into a seamless mosaic of
the lakebed (i.e., plan view image of sonar data). Raw side scan sonar data processing consisted of
corrections for towfish layback (i.e., the distance between the towfish and the DGPS antenna), data
adjustments for signal attenuation, and sonar imagery georeferencing (i.e., projection of the sonar data
into real-space coordinates). Water column portions of the acoustic returns were removed through
inspection and digitizing the nadir (first surface return from the lakebed) for each channel on a survey
transect. The raw data were then position corrected by applying the measured offset between the
DGPS antenna and the towfish to each of the data files. Georeferenced transect data and mosaics were
created from these processed data (Figure 26).
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