Validation of a high-resolution acoustic imaging sonar method by estimating the biomass of submerged plants in shallow water

Acoustic sensing is often used for mapping and monitoring aquatic plants in shallow waters. Recently, high-resolution imaging sonar was applied to study a variety of aquatic organisms. This method can provide high-resolution, three-dimensional (3D) acoustic data on the spatial distribution of submerged plants. However, no commercial software packages are available to digitalize the images of submerged plants generated from imaging sonar data, and the high-resolution imaging sonar method has not been standardized because of a lack of empirical data. In this study, we measured the biomass of submerged plants in the north basin of Lake Biwa using high-resolution acoustic imaging sonar and compared the results to directly measured biomass values to validate the utility of high-resolution acoustic imaging sonar as a quantitative method. Biomass was calculated in 10 randomly selected quadrats (1 x 1 m) in Lake Biwa. The analysis of the resulting data indicated a strong correlation between the number of pixels in the digital images of submerged plants and their directly calculated biomass (R-2 = 0.91, p < .0001). The results suggest that the high-resolution imaging sonar method is a promising tool for estimating the biomass of submerged plants. Thus, this method is expected to contribute to a better understanding of aquatic ecology.