An Acoustic Ocean-Transport Meter

An acoustic method is discussed for measuring mean currents by accurately measuring time-of-flight differences for sound to travel in two opposite directions along a path in the ocean. The acoustic path is a "sing-around" vertical triangle with a base about 3 km long; the determines the mean horizontal component of velocity averaged through the water column. The measurements are made by adapting a programmable inverted echo sounder (IES) and two transponders. These are used in a master/ slave mode where the IES transceiver records all data and provides the timing reference. The two slave transponders are each located -3 km from the master, all near the bottom. Each master / slave pair and the ocean surface form two vertical triangular "sing-around" loops whose planes are orthogonal. The sources of error such as detector scatter, mooring motion, and variations in sound speed are discussed. The results of the field tests are presented along with comparisons against Pegasus vertical profiles of velocity.