Reciprocal acoustic transmissions: Instrumentation for Mesoscale monitoring of ocean currents

By simultaneously transmitting acoustic pulses in opposite directions between two points in midocean, one can separate the effects of ocean currents on acoustic propagation from the effects of sound-speed structure. Reciprocal acoustic transmissions can therefore be used to measure ocean currents. Acoustic transceivers have been designed and built to measure the mean currents between two points separated by 300 km. The equipment functioned satisfactorily during a sbort test conducted during 1983. Preliminary analysis of that experiment has yielded differential travel times that appear reasonable, but more work is required to relate the differential travel times to meaningful ocean-current estimates.