Doppler characteristics of sea surface reflected and scattered acoustic signals induced by surface wave motion

The frequency spectrum of surface forward-scattered and surface backscattered underwater acoustic signals is examined for predicting the state of the ocean surface. Previous measurements of forward-scattered sound show a relationship between the frequency spectrum of the received acoustic signal and the frequency spectrum of the sea surface waveheights under conditions of small Rayleigh parameter. Experimental and theoretical studies predict that the surface reradiated signal spectrum is spread in frequency and consists of a specular component centered at the transmitted frequency and sidebands that are the result of scattered near-specular incoherent energy. Measurements of acoustic backscatter show the scattered frequency spectrum to be Doppler shifted from the transmitted signal in a direction that is dependent on the orientation of the acoustic source and receiver with respect to the directional spectrum of the sea surface waves. The measurements of both forward-scattered and backscattered acoustic signal spectra are studied and related to the monitoring of the state of the ocean surface