UC Santa Cruz

In acoustic remote sensing, the seabed frequency-domain reflection coefficient contains significant geoacoustic information, namely the depth and frequency dependence of sediment sound speed, density, and attenuation. Typical reflection measurements are performed with a towed source and/or receivers to obtain a range of seabed reflected angles. It is shown here that the measurements can be performed using a hull-mounted low-frequency multibeam sonar with an offboard fixed or drifting hydrophone. To obtain the reflection coefficient (as well as scattering strength and other quantities of potential interest), the multibeam sonar radiation pattern must be known. Radiation patterns and absolute levels of the Kongsberg SBP29 multibeam sonar are measured and reflection coefficient measurements are presented in two geologically dissimilar environments, the Eel River shelf, CA and the Santa Barbara Basin, CA. The reflection coefficient frequency and angle dependences are explored via forward modeling to determine regions of the data space that contain information about the geoacoustic properties.