Zooplankton abundance measurements from acoustic Doppler current profilers

In a pilot intercomparison study, C. N. Flagg and S. L. Smith (1989) showed for the first time that under optimal conditions acoustic Doppler current profilers could produce zooplankton biomass estimates with considerable accuracy and resolution. Optimal meant that the profiler was bottom mounted and thus operated in a low-noise environment, that the 307-kHz operating frequency was relatively high and thus more sensitive to small scatterers, and that there was little chance for variations in size class distributions over the short deployment interval. In the present work, the authors extended the investigation by increasing the database for intercomparison with a long-term deployment during which there will be significant size class changes and by an extension of the techniques to 150-kHz shipboard systems. Preliminary results confirm the pilot study for the bottom mounted units. The 150-kHz shipboard units have also been shown to produce good results, although they appear to be less sensitive than the 307-kHz units.