Suspended sediment transport plays an important role in the coastal environment evolution. Thus, the observation of suspended sediments is of interest to coastal scientists, engineers, conservationists and planners, in their activities of harbour construction, land reclamation, coastal protection and coastal zone management. For the past two decades, optical and acoustical techniques have been applied to the measurement of the suspended sediment concentration (SSC) in ocean waters (Proni et al., 1975; Hay and Sheng, 1992; Lynch et al., 1997). Transmissometers and optical back scatters (OBSs) have been developed for point measurements, with some interference to the water column. On the other hand, the acoustic back scatters (ABSs) have an advantage of using a single sensor to obtain SSC profiles without disturbing the water column. Acoustic Doppler Current Profilers (ADCPs), originally designed for measuring three-dimensional current velocities, also have potential to retrieve remote SSC data. The backscatter data form the ADCP i.e. the echo intensity, have been used to measure the SSC by Thevenot and Kraus (1993). They deployed a 2.4 MHz Broad Band ADCP and a transmissometer at a station in the Chesapeake Estuary and found that the ADCP was capable of measuring SSCs with accuracy comparable to the transmissometer, especially when the concentration exceeded 50 mg L^-1.

The ADCP is mounted on a vessel moving at a speed of 2-3 ms^-1 was used to measure the profile of suspended sediment concentrations (SSCs) at the entrance to Jiaozhou Bay, Shandong Peninsula, where the water is characterized by low SSCs (bellow 30 mg L^-1), even during spring tides. The echo intensity data produced by the ADCP were regressed against the SSCs collected in situ and derived using the filtration method, in order to establish an algorithm to transfer the acoustic signals (i.e. the echo intensity data) into SSC data. The results show that the calibrated relationship can be used to calculate the SSC, with a relative error of 30%. Therefore, it is feasible to measure the SSC (even if the concentration is low) using the ADCP mounted on a moving vessel. Compared with OBS, ABS and other instruments for SSC measurements, the ADCP represents a potentially powerful tool to retrieve SSC data in continental shelf waters.