Real-time reverberation inversion for acoustic seabed properties

Accurate environmental information is required for obtaining reliable predictions for the performance of low-frequency active sonar (LFAS) systems. This environmental information is, however, often unreliable or unavailable. For example, the acoustic seabed parameters relevant for the scattering and reflection of sound at the seabed are commonly deduced from a coarse map or database, only providing a rough indication as a result. Echo sounders can provide real-time information on acoustic seabed properties. Nevertheless, since an echo sounder operates at different frequencies and only covers the area underneath the ship, one may question whether the echo sounder provides reliable input for LFAS sonar performance prediction. Within the EDA Rumble-2 project, a through-the-sensor approach has been developed. A demonstrator system has been constructed that determines relevant acoustic seabed parameters from the LFAS reverberation data in real time. As a result, the information is directly available for the assessment and prediction of the sonar performance and can be used as a tactical decision aid. The demonstrator system is validated in several sea trials conducted off-shore Bergen in Norway. These trials demonstrate that the obtained seabed parameters have a good correspondence with ground truth information available for this area. In addition, consistent results for the acoustic seabed parameters are obtained in trials conducted in June and October with different environmental conditions. This suggests that the results can be used for reducing the uncertainty in reverberation and transmission loss prediction.