Great Bay Single Beam bathymetric survey
Summer 2009
*Data is supplied as-is and is not warranted for any purpose including navigation
Contact: Paul Johnson
A bathymetric survey of Little Bay Estuary was conducted on 16 days in the months of February and March of 2013 using a dual-frequency (24 and 200 khz) single-beam sonar system. The survey extends from the General Sullivan Bridge to Adam's Point, and spans the width of the estuary to within 20-50 m of the high tide shoreline.
A total of 360 cross-estuary transects spaced at 20 m intervals were transited by the R/V Galen J, a 22 ft shallow-draft vessel equipped with the sonar system and differential GPS receiver with accuracy of 1-5 cm (based on RTK base corrections transmitted to the vessel from a nearby GPS base station). Sound speed corrections were applied to processed sonar data, and were determined from CTD casts obtained several times during each survey.
Full waveform backscatter intensity data from each sonar ping were recorded at about 14 hz. Bottom depths below transducer were determined from the 200 khz data with estimated accuracy of about 5 cm. Sonar depths were combined with GPS positioning to determine bathymetric maps with total uncertainty of about 10 cm. Surveys were referenced to the WGS84 ellipsoid. Backscatter data from each sonar frequency were also interrogated to estimate the maximum intensity, total integrated intensity of the bottom return, and width of the bottom return in an effort to begin examination of the acoustic signatures of the Little Bay bottom types (the subject of ongoing research).