ExREI (Extended Range Environmental Interrogator) for Accurate Sound Velocity Profiling

The U.S. Department of Defense (DoD) uses a number of acoustic systems required for communication and sensing applications subsea. In order to most effectively use these acoustic systems, there must be a good understanding of the sound speed throughout the water column. The water temperature and salinity profiles vs. depth are the critical factors that influence the speed of sound in a body of water. Sound speed is highly variable in the upper part of the water column, where seawater temperature and—in the Arctic, especially—salinity can be both highly variable and dynamic in time and geographic location. Having an accurate real-time means of measuring the seawater temperature, and thus the sound speed in this upper part of the water column will provide critical information to improve vulnerability assessments of subsea platforms, and improve acoustic the effectiveness of surveillance systems. Moreover, geo-referenced, time-tagged seawater temperature and sound velocity profiles collected over time in areas of interest enable improved accuracy of Naval Oceanographic predictive models, and mission planners to more properly plan operations within an area, based on observed seasonal trends and patterns. To address this critical gap the Makai team is developing the ExREI (Extended Range Environmental Interrogator), a robust, reusable tether-based sensor that is interrogated to provide key environmental measurements that are processed in combination with the host UUV hotel sensors to generate accurate and timely sound speed profiles in real-time.