INFLUENCE OF DE-COHERENCE EFFECTS ON SONAR ARRAY GAIN: SCLAED EXPERIMENT, SIMULATIONS AND SIMPLIFIED THEORY COMPARISON
Résumé
Our study focuses on the subject of acoustic wave propagation through spatially fluctuating ocean. The fluctuations are here linear internal waves (LIW) and we developed an experimental protocol in water tank in order to reproduce the effects of LIW on ultrasound propagation. The present paper gathers the results obtained in terms of coherence function (second-order moment) for various configurations. Typical regimes of the ΛΦ plane developed by Flatté were explored, resulting into coherence function becoming narrower as the saturation increases. We also relate the coherence function to an array gain degradation parameter, δAG, which accounts for how the system performance will be mitigated in a given configuration. δAG was calculated for various sizes of vertical linear array (VLA) and showed an important dependence on the VLA's length. Typically, in any case (scaled experiment, computer simulations and simplified theory), we note that the longer the VLA, the greater the corresponding δAG. Moreover, as the saturation induced by medium fluctuations increases, δAG increases as well. This highlights the need for corrective signal processing techniques when large VLAs are used in a fluctuating environment. Signal processing techniques from various domains (e.g. adaptive optics, radio) are also studied.
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