A study on the range performance of acoustic Doppler current profilers

The range of an acoustic Doppler current profiler depends on several factors, e.g. on the level of the power output and on the acoustic backscatter level. In this article results from a study on the range performance of a profiler are discussed. Two tests were carried out in October, a time of year when Norwegian fjords are fairly clear. The tests showed that the range of the instrument changes significantly during short periods of time, follow the biological rhythm of zooplankton. To avoid predators, the zooplankton migrate down the water column during the day and up during the night (diel vertical migration). When the acoustic backscatter level was at its highest, the range was longer than the specified maximum range. During day, the maximum range was almost halved compare to the range at night. The output's power level had less influence on the range than the backscatter level. Almost the same range was obtained in low power mode as in high power mode.