Current measurement by differential acoustic travel-time reviewed

Since 1977 papers have been published and talks presented about measurement of fluid flow by differential acoustic travel-time. The technique is older than these publications but a compilation of these will serve as a research source for understanding the development of the technique through 2014. The earliest papers describe the differential acoustic travel-time technique as applied to a free-fall shear meter and then to a boundary layer array. Next are the benthic boundary layer studies that gave rise to the BASS tripods and their application to the deep-sea sediment transport problem. Deep-sea applications transitioned to shelf depths and the combination of waves and current in estimates of bottom stress. Studies of the upper boundary layer used bottom tripods suspended from surface floats or mounted on tower legs to study air-sea interaction and mixing under waves in the surface boundary layer. Free drifting velocity sensing arrays were deployed to study internal diapycnal mixing. There are a series of papers about Richardson number measurements from RiNo floats. Finally the development of a compact single-point sensor based upon the differential acoustic travel-time technique is described in papers that progress through analyses of performance and enhancements as well as applications of the Modular Acoustic Velocity Sensor, MAVS.