Woods Hole Group was contracted to perform bathymetric and side scan sonar surveying of a proposed cable route in the lower Narragansett Bay.  The purpose of the survey was to map the bottom bathymetric features of the cable corridor, to report any significant cable obstructions, and to calculate the length of cable required to cross the seafloor.  The bathymetry was conducted using a differential Global Positioning System (GPS) linked to a high precision fathometer through integrated navigation software running on a laptop field computer.  Vertical control was obtained by deploying a tide gauge near the study region for the duration of the survey.  The tide data were used to adjust the raw soundings data to remove the influence of tidal height variations.  The bathymetry data were collected along a series of transects spaced 20 meters apart.  Both east-west and north-south transects were run to tie the survey lines together.  Dual-channel side scan sonar imagery of the seafloor in the vicinity of the cable also was obtained.

The survey tracklines were designed to provide 100% overlap of the side scan images between adjacent tracklines.  The side scan images were evaluated for obstructions in the vicinity of the proposed cable route, such as the boulders and sunken dinghy in the image to the right.  A computer program was developed to calculate the desired cable length.