Assessing the Reliability of ADCP-Derived Echo Intensity Under Variable Scattering Conditions: Roles of Sediment, Zooplankton, and Bubbles

초록

An acoustic Doppler current profiler (ADCP) is widely used to measure current velocity and estimate suspended particulate matter (SPM) through echo intensity. However, acoustic signals are affected by diverse scatterers, including sediments, zooplankton, and vessel-induced bubbles, which can alter data reliability. This study evaluates the influence of these scatterer types on mean volume backscattering strength (MVBS) and Percent Good (PG) using moored observations in Onsan Bay, Korea. The analysis revealed that PG and data reliability followed the order: suspended sediments > vessel-induced bubbles > zooplankton. Sediment-dominated periods maintained high PG (> 89%) due to the homogeneous size and density of fine particles, ensuring stable backscatter even at high SPM. Zooplankton aggregations caused irregular scattering and marked PG reduction, especially when MVBS < - 60 dB or SPM > 70 mg l(-1), increasing measurement uncertainty. Vessel-induced bubbles produced short-term PG decreases but minimal long-term degradation. PG threshold selection strongly influenced SPM flux estimates under zooplankton-rich conditions. Applying PG > 50% reduced overestimation to < 10% compared with PG > 70%, whereas unfiltered data overestimated flux by 128%. These findings highlight the need for adaptive PG thresholds tailored to environmental conditions to improve the accuracy of ADCP-based SPM monitoring in dynamic coastal environments.

키워드