Evaluation of a vessel-mounted acoustic doppler current profiler for use in rivers and estuaries

A shallow water, 1.2 Megahertz Acoustic Doppler Current Profiler (ADCP) specifically designed to provide earth-referenced water velocity profiles from a moving vessel was evaluated. The ADCP is a four transducer system with a 1-m depth cell resolution and a depth range of 4 to 29 m. Velocity data are recorded and processed using a microcomputer based data-acquisition system. Lake and river tests indicate that the ADCP provides a good measure of velocity during low- to medium-flow conditions (15 to 100 cm/s), providing that an averaging interval of 20 s or more is maintained. The ADCP short-term random error using a 1-s averaging period was determined to be 6.5 cm/s, but was reduced to 2.3 cm/s by using a 20-s averaging period. The ADCP system should be usable for making moving-boat discharge measurements. Some ADCP velocity bias with depth was detected during some river tests which indicate that further tests at higher river flows and in temperature and salinity stratified water are needed to completely evaluate this ADCP.