Research Of Buried Targets Detection Technology Based On Parametric Array

The detection of small buried objects such as mines is much more difficult than that of objects in water due to the high backscattering noise generated by the sediments at the seabed and the high compressional wave attenuation in sediments. Classification of buried objects is also more difficult since acoustic shadows do not exist and since scattering from oblique target surfaces is not detectable. Therefore, acoustic detection of targets is greatly affected due to background noise and seabed reverberation especially in shallow sea. In the worst circumstances, UUV (Unmanned Underwater Vehicle) equipped with sonar systems which can approach buried targets must be applied to detect and classify buried targets effectively. For this sake, the dissertation devises a small acoustic phased parametric array in shallow sea, which can be equipped on the bottom of UUV to detect buried targets.The main content of this dissertation is described as follows:1. With Westervelt's acoustic model, the dissertation studies basic theory of acoustic parametric array technology. The comparison of directivity between parametric array and circular piston transducer array is also given. In order to lucubrate parametric array, a 9-unit parametric array is designed and the relevant experiments are also made.2. A sonar system which is installed on the bottom of UUV is devised in order to detect targets buried in the seabed sediments. This system comprises a parametric linear array for transmitting which can produce high-directivity low-frequency acoustic wave, transducers for receiving high-frequency acoustic wave and a wide-band planar array for receiving low-frequency acoustic wave. This dissertation gives detailed analysis and numerical emulation of the structure and performance of the sonar arrays. With phase array beam-steering technology and side-scan sonar imaging principle, 2D images of buried targets by multiple steering angles can be produced to enhance the detection probability.3. When UUV with the sonar system are detecting targets, we must make sure that the motion is uniform linear and the attitude of the bottom sonar is stable. The dissertation uses 3D electronic compass to measure the attitude data of UUV, which will be given to the controlling mechanism to adjust the attitude of UUV and will be combined with the sonar detection data to produce 2D images of targets. Therefore, by this method, the quality of imaging and detection probability will not be reduced due to attitude instability when UUV with the sonar system are detecting targets.