Autonomous quantification of kelp biomass on offshore aquaculture installations using side scan sonar

In recent years, global demand for macroalgae has grown as a sustainable food resource, potential tool for marine carbon dioxide removal (mCDR), and various pharmaceutical and cosmetic applications. Traditional commercial macroalgae monitoring is time-, labor-, and cost-intensive, with manual inspection limited to surveying small areas and shallow depth ranges. While advanced acoustic technologies such as side scan sonar (SSS) have long been established as a tool within the fishing industry, sonar use in commercial macroalgae aquaculture has been limited. Sonar allows for broad scales of qualitative and quantitative measurement and thus will be an important component in autonomous monitoring of offshore aquaculture installations to assess infrastructure integrity and crop growth. Here, we present a method for the analysis of side scan sonar observations on a commercial macroalgae installation. We utilize geometric principles to estimate kelp height on each farm line and approximate standing biomass. Our algorithm is applied to a commercial kelp installation offshore of Santa Barbara, California, validated with in situ measurements. Our work provides a stepping stone for increasing efficiency and informed decision-making of large-scale kelp installations, decreasing cost and labor for farmers in the face of a higher market demand.