Multitemporal Acoustic Backscatter Data Analysis to Monitor the Dynamics of Seabed Surface Sediments

Backscatter strength is a product of underwater acoustic remote sensing. This study used a multibeam echosounder as an acoustic remote sensing instrument to collect backscatter strength data. These data are then used to classify the surficial sediment distribution. To monitor the difference in seabed sediment distribution, a time-series survey was performed to obtain multitemporal acoustic backscatter data. An EM 304 multibeam system from Kongsberg was mounted on the Research Vessel Baruna Jaya III from the Indonesia National Research and Innovation Agency (BRIN). It was used to collect backscatter data in the waters of Raja Ampat, Indonesia. The data were collected at different times, April and July 2021. Geometric and radiometric corrections were applied to these backscatter data. Based on the angular response curve analysis from acoustic backscatter strength, the research area can be classified into four seabed sediment types: boulder, gravel, sand, and mud. A comparison of both time series backscatter data shows that the boulder and gravel areas increased by 13.6% and 19.0%, respectively. Elsewhere, the area with sediment types of sand and mud diminished by 30.5% and 2.0%. The change in the sediment type area occurred as much as 50.5%, while the remaining 49.5% area remained unchanged. This resulting value is apparently derived from the steep topography that rapidly changes sediment distribution. One such suggestion is that sediment sampling should be performed to confirm the model from angular response curve analysis.