CHIRP Versus BURST Sonar Resolution Techniques for Classification During Detection
DALMO VICTOR TEXTRON BELMONT CA
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A previous Dalmo Victor report, R-2850-2931, proposed the CHIRP pulse compression technique as most adequately resolving detection range, classification and range rate problems for search sonars. This report qualitatively evaluates the effects of propagation non-linearities and Fresnel zone target scattering interference on CHIRP resolution. Comparisons are made to a BURST short pulse train system. For equal resolution, both techniques require equal bandwidths and similar spectral amplitude distributions. BURST resolves signals from different range cells by phase or time difference alone CHIRP by both time and frequency. Propagation non-linearities cause similar coherence loss and resolution broadening. Scattering is a linear process. CHIRP resolves overlapping long pulse echoes by superposition of time-frequency separated signals. It is concluded that CHIRP provides resolution equivalent to BURST for a given sonar bandwidth. CHIRP permits use of a long, low data rate, detection pulse. In addition, the coherent integration used in a CHIRP system provides a greater target detection range than can be achieved with the non-coherent integration used in a BURST system, for the same average power. CHIRP also permits removal of range rate by triggering the classification display sweep at receipt of the first compressed CHIRP echo.
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