Aircraft laser sensing of sound velocity in water: Brillouin scattering

Abstract

A new real-time data source for sound speed in the upper 100 m has recently been proposed for exploratory development at the Naval Oceanographic and Atmospheric Research Laboratory. This data source would be generated via a ship- or aircraft-mounted, optical pulsed laser using the technique of spontaneous Brillouin scattering. This system should be capable (from a single 10 ns 500 mJ pulse) of yielding range resolved (≈ 1 m resolution) sound speed profiles in water to depths of 75–100 m to an accuracy of 1 m/s. At aircraft speeds of 300 miles/h (134 m/s) and a laser pulse repetition rate of 10 pps, vertical profiles of sound speed would be obtained spatially every 13 m. These 100 m profiles would provide the capability of rapidly monitoring the upper-ocean vertical structure for much of the world's oceans and for most seasons. They would provide new perspectives on upper-ocean mixing and the oceanic internal wave field. These profiles would also provide an extensive, new, subsurface-data source to existing real-time, operational ocean nowcast/forecast systems. The present systems are dependent on sparse bathythermograph data and information inferred from sea-surface data. Extension of the 100 m profiles to depth using existing and proposed techniques would further increase the value of the laser-derived information.