Multibeam water column filtering methods to improve data management and bio-acoustic interpretation

Abstract

Water column acoustic return data from a 400 kHz Reson 7125 SV2 multibeam sonar was examined within the Mississippi Bight to identify and map biomass throughout the region. The multibeam sonar acoustic data are traditionally considered relative measurements of water column scattering or impedance contrasts, which are difficult to correlate directly with biological and physical properties of the water column. To overcome this constraint, the multibeam sonar data has been collected simultaneously with imagery from a towed profiling In Situ Ichthyoplankton Imaging System (ISIIS) (with CTD, dissolved oxygen, PAR, and chlorophyll-a fluorescence sensors). There are many technical challenges associated with correlating the two datasets, as the multibeam sonar data are in three dimensions, they provide outputs on different temporal and spatial scales, and the acoustic scattering patterns are challenging to identify and extract. Developing an efficient and robust filtering algorithm to identify biologically and physically dynamic areas of interest requires tackling issues with scattering artefacts, such as transmit and receive beam pattern effects and the patchiness of water column layers. The goal of this work is to correlate the sonar data to imagery data from the ISIIS, and other sensor information, expanding the potential applications of multibeam water column data to include identification of scattering features and examination of fine scale oceanographic processes.