Ocean Current Profiling With A Shipboard Doppler Acoustic Backscatter System

An acoustic Doppler backscatter current profiler and associated data logging equipment were recently installed aboard the NOAA research vessel RESEARCHER. The system transmits 115 KHz acoustic pulses from a hull mounted three beam transducer and measures the doppler frequency shift of the backscattered signal as the pulses propagate down through the water column. The motion of the water is then computed from the Doppler frequency shifts to yield a profile of the relative currents beneath the ship. The system has been operated extensively in the Straits of Florida and the eastern equatorial Pacific Ocean in conjunction with other current profiling instruments.Maximum effective depth penetration of the acoustic profiler was approximately 250 meters and good agreement was obtained with the other profilers over this depth range. Although the conversion from ship-referenced to absolute current profiles is hampered due to the lack of reliable, continuous navigation coverage over wide areas of the ocean, the data to date has proven to be scientifically interesting and useful. The referencing problem should be alleviated in the future with the implementation of newer satellite navigation systems.