Design and tests of a trawl-resistant package for an acoustic Doppler current profiler

A package designed to protect an RD Instrument Ltd. acoustic Doppler current profiler survived several passages of a bottom trawl. The package, in the shape of a truncated pyramid, has a base 4 m by 3.3 m and a height of 53 cm. The authors describe the package, its deployment method, and field test results where a trawl was repeatedly dragged over the unit. The device has been used successfully three times on the continental shelf. Some acoustic measurements were also made to ascertain the effect of the package on the beam pattern. The results show that this design can protect the instrument from bottom trawls and the acoustic beams are minimally affected by the plastic plate in front of the instrument transducers