Nearfield performance of passive correlation processing sonars

Abstract

Passive correlation processing sonars in which the distance of a moving source from the receivers is not appreciably greater than the inter-receiver spacing are considered. In the simplified case, where two receivers are employed, the processor chooses one of the received signals as a reference and adds a corrective time delay and Doppler shift to the other signal before the correlation operation is performed. When the processor selects a time delay and Doppler shift corresponding to that present in the signals, the correlation function has a peak. The degree of correlation between the two signals is measured with the use of a passive uncertainty function. An approximation is made for narrow-band signals which is computationally advantageous. The effects of time delay and constant Doppler shift are discussed, and the degradation resulting from time varying Doppler shift is derived and plotted. Results are presented for both sinusoidal and narrow-band type signals. A technique of plotting contours of maximum data integration time is developed and shown to significantly reduce the complex problem of studying scenario geometries.