A Study of Active Sonar Reverberation using Ultrasonic Experiments in a Shallow-water Tank

This paper describes a study of active sonar reverberation level (RL) estimates made using scaled ultrasonic water-tank data. Such laboratory experiments provide a means of upper bounding the performance of RL estimates made in real shallow-water ocean environments. An ocean-to-tank scaling factor of 1000:1 was used to model a 180-220 Hz active source in a 100 m. deep, 2 km. extent of ocean using a 180-220 kHz. ultrasonic source in a 2 m. diameter tank filled to 0.1 m depth. Time-frequency analysis of backscattered ultrasonic data yielded intensity striations which compare favorably with theoretical models. Reverberation level (RL) estimates were computed as a function of frequency and range for both conventional frequency-invariant processing and more recently proposed waveguide-invariant processing. Experimental results indicate that waveguide invariant RL estimates provides an average 8 dB mean-square-error improvement over conventional methods.