The development of acoustic mapping of ocean currents in coastal seas

Coastal oceanography is characterized by a high spatial and temporal variability, limiting the observational and predictive capability for environmental protection. Among various measurement techniques for studying ocean dynamics, the method of ocean acoustic tomography (OAT) is particularly useful for obtaining the spatial variation of current fields in the ocean interior. Traditionally, with only a limited number of the moored acoustic tomographic sensors, the inversion of currents in coastal areas still suffers insufficient sampling of the water volume. Recently, incorporating a ship-towed sensor has attracted considerable attention due to their capability of resolving the small spatial scale of ocean features. In this talk, we will review the fundamentals of moving ship tomography and signal/data processing algorithms for current estimation using the difference of reciprocal travel times. The central idea is to increase the number of ray paths that sample the ocean column at various angles, per the projection slice theorem. The concept has been further extended by using an autonomous underwater vehicle (AUV) or an unmanned surface vehicle (USV) as an alternative carrier for the sensor. This configuration has been demonstrated by recent experiments. This talk concludes with a discussion of future research activities and applications.