Comparison of acoustic backscatter measurements from a ship-mounted Acoustic Doppler Current Profiler and an EK500 scientific echo-sounder

We compare the calibration of a 150 kHz RD Instruments Acoustic Doppler Current Profiler against the 200 kHz channel of a SIMRAD EK500 scientific echo-sounder. Over a range of mean volume backscattering strength of -88 to -68 dB (relative to a scattering cross-section of 1 m(-1)), from 10 to 90 m depth, the data from the two instruments were well correlated but with significant slope and offset errors (approximate to 10% and +/- 3 dB, respectively). After correction for these systematic errors the residual differences between the ADCP and the EK500 were less than 1 dB. This accuracy is sufficient for many qualitative studies of the coupling of ocean physics and biology. (C) 1996 International Council for the Exploration of the Sea.