Experimental investigation of a high resolution sonar
Huat, Lim Chin
Walters, Donald L.
Atchley, Anthony A.
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This thesis investigated a laboratory synthetic aperture sonar designed to test the algorithms and techniques needed to detect, classify and identify minelike objects. Previous synthetic aperture sonar work at NPS achieved 5 cm range resolution and 1 cm azimuth resolution. This thesis developed a pulsed, frequency modulated, synthetic aperture sonar that achieved range and azimuth resolutions of about 1 cm. The processed images clearly reveal targets with a high degree of certainty. However, the ability to classify and identify mines and rocks is less certain because of speckle and glint effects. The high resolution algorithms improved the detection and overall image quality of targets, and achieved a signal to noise ratio of 35 dB. The 2:1 frequency spread of the FM chirp increased the signal to noise ratio by 20 dB compared to an unfocused synthetic aperture system. However, a significant finding is that resolution alone is not sufficient to classify and identify minelike targets in complex backgrounds. Resolution of this problem will require a different approach such as utilizing adaptive acoustic daylight to avoid the speckle and glint problems inherent with coherent illumination. To achieve a classification and identification capability, a completely different approach to acoustic illumination and signal processing is needed.
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