SOME ASPECTS OF THE DETECTABILITY OF BROADBAND SONAR SIGNALS BY NONDIRECTIONAL PASSIVE HYDROPHONES
RAND CORP SANTA MONICA CA
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This Memorandum deals with some of the problems arising in the passive detection of submarines by single, nondirectional hydrophones. The signal emitted by the submarine is assumed to be a broadband noise whose characteristics are similar to those of the background noise. Hence, detection is possible primarily because of the increase in noise power caused by the presence of a target. The effects of the motion of the submarine past the hydrophone and of the uncertainty in the background noise level are analyzed. Although the observation time for a slowly moving submarine is greater than that for a fast submarine, it is found that if there is uncertainty about the background noise level, detectability is essentially independent of observation time. Hence, a faster and therefore noisier submarine is more easily detected than a slower and quieter one. The major factor limiting the detection range is the noise uncertainty but if the background noise is stationary, the fact that the signal produced by the moving target is a nonstationary noise can be used by the detector to estimate the background noise, and therefore to increase the detectability.