Acoustic detection of macroalgae in a dynamic Arctic environment (Isfjorden, West Spitsbergen) using multibeam echosounder

Acoustic imaging of seabed morphology and benthic habitats is a fast-developing tool for investigating large areas of underwater environment. Shallow, coastal bottoms are especially difficult to map, while only small boats can be used around these zones as research platforms. Working with a traditional multibeam echosounders from small open motorboats is a big challenge and has a lot of limitations in terms of equipment size and installation. Recent development of compact devices overcome this problem and allow for collecting high resolution and good quality acoustic data, ensuring quick mobilization and demobilization of the instrument with keeping hydrographic measurements up to IHO standards. Development of methodology and signal processing for underwater environment monitoring using multibeam echosounders is still an ongoing process, especially in terms of processing water column echoes and snippets. Very important tasks nowadays are detecting benthic habitats on a seabed and other scatterers in a water column (e.g., fishes, or suspended sediments). This study presents preliminary results of acoustic investigations of macroalgae in coastal zone of Isfjorden, Arctic fjord in Svalbard Archipelago. In Julys of 2016 and 2017 eight areas (4 northern and 4 southern of the fjord) were mapped using single-beam sonar Biosonix DTX (420kHz) and multibeam sonar Norbit iWBMS (330kHz). The project aim was to investigate spatial distribution of macroalgae in areas under the various influence of glacial melt water and was founded by Polish National Science Centre (project MAKAK: UMO-2015/17/B/NZS/02473). We covered 6.6 km 2 of seabed in shallow, coastal zone, collecting a unique data set combining acoustic data with very well correlated ground-truth images (video) and environmental measurements (CTD, turbidity, ADCP). Using signal processing techniques we analyzed bottom morphology, backscatter intensities (snippets) and water column data echoes from Norbit iWBMS sonar showing its capability for benthic habitat mapping. We also would like to demonstrate methodology for mapping and monitoring shallow, coastal areas in the Arctic using compact multibeam systems. We also believe that this methodology can be extended to other nearshore zones.