Development and Testing of an Acoustic Plankton Recorder
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Recent years have brought cross-disciplinary focus on possibilities, constraints and consequences of large scale zooplankton harvesting. Development of acoustic measurement technology is an important part of that work. Because of the small size of the plankton, the measurement frequencies have to be high compared to fishery acoustics. Based on a model of the size and shape of the plankton and its physical properties, the use of multiple frequency measurements will allow inverse modeling of the size and concentration of plankton. This thesis presents the development and test results of an Acoustical Plankton Recorder (APR). The system uses three frequencies, 200 kHz, 710 kHz, and 1 MHz. The system parameters are designed with a focus on measuring the zooplankton Calanus finmarchicus, which plays an important role in the Norwegian Sea ecosystem. The APR is a prototype instrument built to gain experience for future generations of instruments for plankton measurements. Different aspects of multi-frequency acoustical measurements are discussed with a focus on uncertainties and critical factors. The results from various experiments and measurements are presented. The estimated concentration of scatterers from data recovered by the Acoustical Plankton Recorder shows good agreement with biological samples.