SEABOTTOM BACKSCATTER STUDIES IN THE WESTERN CONTINENTAL SHELF OF INDIA

Abstract

In this paper, a study is initiated to observe the interaction effect of the sound signal with three different sediment bottoms in the shelf area between Cochin and Mangalore in the western continental shelf of India. An echo signal acquisition system has been designed and interfaced with the 12 kHz echosounder installed onboard ORV Sagar Kanya. The reflection coefficients including attenuation at the seawater/bottom interface are computed in the three different sediment areas based on the sediment mean grain size. The experimental coherent reflection coefficients are calculated using the attenuation corrected reflection coefficients and the normalized cross-correlation between successive backscatter echo signal waveforms in those areas. Further, analyses conducted by determining the echo peak Probability Density Function (PDF) and matching them with the experimental echo peak histograms provide root mean square (rms) roughness amplitude in the three different survey areas. The rms roughness values are used to compute the coherent reflection coefficients. An attempt to establish concurrence between the coherent reflection coefficients based upon the rms roughness amplitude and the experimental coherent reflection coefficients using the backscatter echo signals, reveals the importance of seawater/bottom interface roughness in the coarse grained sediment bottoms like sand and silty sand. The existence of microtopographic features are responsible for the seawater/bottom interface roughness. However, in the fine grained sediment area, the bottom does not contain any such feature.