Calibration and use of a broadband ADCP to measure zooplankton volume scattering strengths

Abstract

A 1200 kHz broadband ADCP from RD Instruments was calibrated and used to collect quantitative volume backscattering data from zooplankton in the Gulf of Mexico. Voltages on the four receivers, reported in terms of ‘‘counts,’’ were linear with respect to received sound pressure level in dB re 1 μPa, with sensitivities of 2.376 to 2.434 counts/dB, depending on the receiver. Source levels ranged from 212.9 to 214.6 dB re 1 μPa at 1 m. The ADCP was mounted on the C/V Admiral Semmes and used to survey volume backscattering around an oil platform in the Gulf of Mexico. Volume backscattering strengths measured between −40 and −90 dB, which were generally consistent with independent observations of the numbers and sizes of scatterers present in the water column. These results suggest that, with careful calibration, ADCPs may be used for quantitative zooplankton research.