Acoustic properties of macrophytes: Comparison of single-beam and multibeam imaging with modeling results

Macrophytes are an important part of marine habitats, as primary producers and shelter for marine life. Some species, like Laminaria digitata, have acoustic properties very close to water, in terms of density and impedance, but their imaging is possible using high frequencies. This paper focuses on the comparison of multibeam and single-beam measurements of macrophytobenthos in Arctic, using Biosonics DTX (420-kHz frequency) single-beam and Imagenex Delta-T 837 imager (260-kHz frequency). This comparison investigates the role of angular response for bottoms covered by macroalgae, supplementing these field results with measurements of macrophytes suspended in the Arctic water column (i.e. without bottom influence). Detailed measurements of the morphology of dominant, Arctic seaweed species were taken to specify their acoustic properties. Data about mean leaf size, body density and undulations or roughness of macroalgae thallus surface were collected for Laminaria digitata and Saccharina latissima. It helps to estimate how much of the acoustic energy is reflected, absorbed and scattered by the seaweed layer and how much bottom substrata influence this process.