Modelling and signal processing for identification of ocean subsurface features from acoustic reflections

El-Hawary, Ferial M. (1981) Modelling and signal processing for identification of ocean subsurface features from acoustic reflections. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This thesis is concerned with aspects of modeling and signal processing for identifying features of the ocean subsurface layered media on the basis of acoustic reflection data. Techniques from communications and signal analysis are combined with estimation and system theory to develop procedures to estimate the properties and characteristics of underwater sediments and layered strata. -- Models of the response of the subsurface to acoustic or seismic source signals are reviewed and classified. A layer indexed reflection model that accounts for higher order reflections in a systematic manner is detailed. This provides the basis for the estimation task. -- Reflection data are generated and acquired using a towed-body system, the so-called "fish", which contains the acoustic source and sensors. The motions of the deep towed system introduce inaccuracies in the reflection data. The fish dynamics exhibit a degree of regularity which is utilized in the design of a Kalman-based filter for estimating the heave effects. The estimates are then used to remove the heave component from the reflection data. -- The problem of estimating amplitude and delay parameters associated with replicas of the source signal primary and multiple reflections imbedded in the return signal is investigated. Three proposed estimation procedures are given. The first adopts a sequential algorithm where the delay parameters are estimated first followed by those of the corresponding amplitudes. A second approach developed in this thesis involves the simultaneous evaluation of all the parameters of interest. The third procedure is based on a balance property inherent in the source signal waveforms. -- The proposed procedures are evaluated utilizing simulated return records to provide a basis for comparing the effectiveness of each. The application of the procedures to actual field data obtained in a sea-trial in outer Placentia Bay, off the coast of Newfoundland is given.

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