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MAPPING BATHYMETRY AND BOTTOM TYPE IN A SHALLOW ESTUARY
Citation:
Abdelrhman, M. MAPPING BATHYMETRY AND BOTTOM TYPE IN A SHALLOW ESTUARY. Presented at EMAP Symposium 2001, Pensacola Beach, FL, April 24-27, 2001.
Description:
Bathymetry and bottom type are important in characterizing estuaries and their ecology but hard to map, especially in shallow estuaries. Acoustic backscattering was used to remotely sense these properties in the shallow Slocums River Estuary of Massachusetts. Acoustic pulses were transmitted and their reflections from the bottom received by a downlooking 430-kHz transducer attached to a survey vessel. The first reflection defined the depth and type of bottom below the transducer: the peak provided depth, the rising limb hardness, and the falling limb roughness. The estuary was surveyed along transects separated
by 25-100 m, and at a vessel speed and a transmit/receive rate that gave a record every 4-8 m. The records were located to <1 m by a differential global positioning system. A total of 30,000 records were collected from the estuary. Hardness and roughness defined the bottom types, under the assumption that softer bottoms are smoother than harder ones. The data was classified into distinct clusters of these two variables that represented mud, sand, and rock. A global information system mapped the resulting bathymetry and bottom type over the estuary. Preliminary ground truthing supported the general characterization of the estuary.