Nolan R. Davis Joseph Jeffery Fred T. Erskine
Acoust. Div., Code 7142, Naval Res. Lab., Washington, DC 20375-5350
Experimental measurements of ocean surface and bottom backscattering strengths were carried out in the northwestern Atlantic Ocean during July and August of 1990. The experiment used ship-deployed explosive charges to provide ensonification of the ocean surface and bottom over a range of low frequencies up to 1 kHz. Overall the surface scatter results agreed well with the Ogden--Erskine curves, matching the predicted dependence on wind speed, grazing angle, and frequency. At two sites northeast of the Grand Banks the surface scattering strengths appeared to be dominated by volume scattering due to fish. The bottom scattering strengths were observed to have considerable variation in level (up to 16 dB) between different sites. As a function of grazing angle, most of the bottom scattering strength curves paralleled the Mackenzie curve for grazing angles between 20(degrees) and 40(degrees). A moderate frequency dependence of less than 3 dB was observed. Comparisons of the bottom scattering strengths with the Damuth 3.5-kHz echo-character province types yielded no consistent correlations. Comparisons with archival results for the same region yielded general agreement within 6 dB. Comparison of the ship-based and airborne techniques showed that they yielded comparable scattering strengths to within 5 dB.