Contributions to the study of two-dimensional spatial coherence as part of the development of a low-frequency synthetic aperture sonar

Overview & Synopsis

First applied to light, the notion of spatial coherence is related to the degree of correlation between two signals acquired at two points in space. In the field of sonar, spatial coherence is a central concept that affects the spatial resolution of systems as well as the performance of processes such as interferometry and aperture synthesis. The configuration of the sonar system, the signal processing parameters, and external disturbances such as changing environmental conditions all affect spatial coherence. In the field of mine countermeasures, low-frequency synthetic aperture sonars are currently being developed, in particular to detect buried objects. The aim of this thesis is to develop an analytical model of the spatial coherence of such systems. To this end, existing models developed for vertical acquisition geometry have been extended to be compatible with lateral acquisition. However, in lateral geometry, geometric decorrelations not taken into account in the model reduce the level of coherence. For this reason, numerical modelling of the signals is proposed in order to study the influence of these decorrelations and to estimate the coherence levels after compensation for the geometric decorrelation phenomena.