Measurements of the material properties of live marine organisms and their influence on acoustic scattering

Accurate acoustic interpretation of zooplankton scattering data requires a reliable knowledge of the material properties of the zooplankton. The lack of ability in predicting or measuring in situ material properties of these marine animals greatly affects and limits the capability to estimate the zooplankton biomass acoustically. To provide in situ measurements of the material properties, a new apparatus, the Acoustic Properties Of zooPlankton, (APOP) was developed. The system combines acoustic and resistivity measurements and can be used for in situ applications. This system can be operated under various environmental conditions (temperature and pressure). In addition, a new method (dual-density) of measuring density of live zooplankton is presented. A series of laboratory and in situ measurements were made on various marine organisms using the APOP system. The results from these measurements suggest that the material properties obtained from laboratory measurements, even if they are accurate and reliable under certain environmental conditions, may vary significantly in the ocean under different environmental conditions. Therefore, to correctly model and interpret the zooplankton acoustic survey data, one needs to take into account the variations in zooplankton material properties as a function of the environmental conditions, or oceanographic parameters