Acoustic characterization of submerged aquatic vegetation

Abstract

The acoustic characteristics of submerged aquatic vegetation (SAV) were investigated in order to enhance the performance of mine-hunting and weapon sonars in littoral reglons. The specres of seagrass initially studied was Zostera marina. Laboratory measurements of target strength and backscatter were made under controlled conditions in an acoustic tank. Experimental target strength measurements compared well to the theoretical value. Target strength for an individual blade of Zostera was measured to be approximately -21 dB from 300-700 kHz. No frequency dependence was found in this range. Beam patterns for rndividual specimens were also generated and displayed a strong dependence on blade orrentatron. In-situ measurements were carried out in the shallow water eelgrass beds of Narragansett Bay wrth both side-scan and szngle beam sonars. These experiments clearly illustrated the backscatter and potential masking effects of submerged aquatic vegetation in the 100-400 kHz frequency range. This experimental data will ald in the verification of theoretical models and in the development of methods to enhance the performance of mine-hunting and weapons sonars. The data will also supply environmental input to range-dependent sonar models and enhance tactical and environmental databases. Another application of this research zncludes remote sensing of seagrass beds to monitor pollution and aid in species distribution and density studies.