Intercomparison of acoustic and electromagnetic current meters during leeway drift tests

The U.S. Coast Guard Research & Development Centre (USCG R&DC) and Analysis & Technology, Inc. (A&T) have been investigating technigues to estimate the leeway drift of targets for possible search and rescue applications. In previous leeway drift studies, the InterOcean S4(R) electromagnetic current meter was used to measure search target velocity relative to the 1-meter surface layer. A recently developed compact Doppler current sensor, the Aanderaa DCS 3500, may provide a new technique to measure the motion of floating objects relative to the surrounding water. The smaller size and larger sampling capability of the DCS 3500 make it a good candidate for use with small leeway targets. Intercomparisons of the DCS 3500 and S4(R) were conducted by towing the meters in-line behind a large leeway target in Long Island Sound and offshore of Delaware Bay. The results of the comparisons reveal that the differences in velocity between the two sensors are within expected variances. However, there does seem to be a slight bias in the direction measured by the DCS 3500 when compared with the S4(R).