Acoustic response of targets in a shallow water, layered, environment: Experimental observations and simple ray model results

Abstract

Synthetic aperture sonar (SAS) data were collected throughout May of 2014 during an experiment in St. Andrew's Bay, Panama City, FL. A brief overview is given of the SAS rail system and procedure used during the “BAYEX14” experiment. BAYEX14 was carried out in a shallow water, layered, environment, where water depth was approximately 8 m with a thin layer of mud (i.e., 0.15-0.30 m thickness) covering a sandy bottom. All targets settled into the mud and came to rest on the mud-sand interface. Scattering data from an aluminum finite cylinder, an aluminum pipe, and solid replicas of an 100-mm unexploded ordnance will be presented and compared to data taken previously in a sand-only environment and to model results. To model the scattered pressure, the ray paths are assumed to experience negligible refraction in passing through the mud layer to the mud-sand interface. However, the much higher attenuation in mud relative to water must be considered along the portion of the ray path in mud. For targets at long horizontal ranges, ray paths that interact with the water-air interface must be included to model an observed modulation of the target strength. [Research sponsored by ONR and SERDP.]