Abstract: Suspended sediment concentration (SSC) is a core parameter in estuarine and coastal sediment dynamics and marine hydrological observation. Using acoustic backscatter intensity from Acoustic Doppler Current Profilers (ADCP) to infer SSC has become a research hotspot owing to its advantages of non-contact operation, high spatiotemporal resolution, and simultaneous measurement of flow velocity and sediment concentration. On the basis of expounding the physical foundations, including seawater sound absorption, acoustic scattering and attenuation by suspended particles, and the backscatter-SSC calibration framework, this paper systematically reviews the evolution of single-frequency, multi-frequency, and acoustic attenuation inversion methods and their algorithms, and compares their advantages and limitations. The error sources in practical applications are analyzed in depth, covering sediment grain size and flocculation, sound attenuation and high-concentration effects, environmental interference from bubbles and temperature-salinity variations, instrument and calibration constraints, and insufficient algorithm universality. Improvement pathways are then proposed from the perspectives of multi-frequency collaborative inversion, grain-size correction and calibration standardization, acoustic-optical complementary observation, the acoustic mechanism of flocs, and data-driven inversion.. The analysis shows that acoustic SSC inversion can achieve high accuracy when the particle size is relatively stable, the attenuation is properly corrected, and in-situ calibration is adequate; multi-frequency and attenuation-scattering joint inversion as well as machine-learning-based intelligent inversion are expected to further broaden its applicability. Nevertheless,the deficiencies of single-frequency systems in decoupling the concentration-grain size coupling, correcting attenuation under high-concentration conditions, and generalizing calibration remain the key bottlenecks hindering its engineering application.

Key words: acoustic inversion, suspended sediment concentration, acoustic Doppler current profiler, acoustic backscatter, sound attenuation, grain size correction