Motion induced coherence degradation in passive systems

The problem of correlation degradation resulting from the motion of a transiting target is addressed. The target is assumed to emit a narrowband signal which is remotely received by two or more signal sensors. The signal compensation controls available in correlation processing are a fixed time delay (to align the two received signals) and a fixed time scale-factor shift (to compensate for doppler difference). Although these controls have proven adequate over small integration integrals, the notion induced degradation will become increasingly severe as the coherence interval is extended. The object of the paper is to determine quantitatively the expected correlation degradation as a function of the system geometry, the signal frequency, the correlation integration time and the nature and characteristics of the target track. For a given system geometry, signal frequency, and anticipated notional characteristics then, an appropriate integration time can be chosen to optimize the correlation processor in some useful sense.