Turbidity estimation from an acoustic backscatter signal in a tropical coral reef system

Abstract

This study investigated the estimation of Nephelometric Turbidity Units (NTU) from backscatter signals in a tropical coral reef system using a 1200-kHz towed Acoustic Doppler Current Profiler (ADCP). In order to perform the estimation, simultaneous acoustic backscatter and turbidity data were collected near the surface (above the pycnocline). Simultaneously, water samples at the same depths were analyzed to determine sediment composition. The results showed that a second-degree polynomial model provided the best correlation (r = 0.69) between backscatter signals and turbidity measurements, highlighting the nonlinear relationship between acoustic signals and turbidity values obtained from optical devices. The reef's bathymetry significantly influenced the seawater turbidity, revealing the importance of physical configuration and hydrodynamic conditions in sediment distribution. From the sediment composition, it was determined that 89% of the total suspended solids are terrigenous sediments. This integrated methodological approach provides a detailed understanding of sediment dynamics, essential for the conservation and sustainable management of coral reefs around the word in a noninvasive way.