Hydroacoustic measurement of detritus from the Delaware Bay estuary

During boreal spring run-off there is a significant quantity of detrital material in the water of the Delaware Bay estuary. Collected samples show that the detritus is comprised of approximately 88% grass, primarily Phragmites australis and Spartina alterniflora. Detrital material was measured hydroacoustically using a 420 kHz digital echosounder, first in a controlled laboratory test and then on site. Controlled tests on both small matted masses and individual grass strands produced signals clearly visible (6-15 dB) above background noise. Field tests were performed using a ship-mounted downward looking sonar and echo integration software to characterize and quantify the detrital biomass by depth strata. A vertical series of plankton nets, slightly downstream of the echosounder, and flow velocity measurements by a 1200 kHz acoustic Doppler current profiler (ADCP) slightly upstream provided ground-truth information of local concentrations