Motion induced coherence degradation in passive systems

The problem of correlation degradation introduced as a result of the track and motional instabilities in a transiting target is addressed. The target is assumed to consist of a narrow-band signal source which is received at two remotely located sensors. The outputs are processed through a correlation-type detector. The correlator output will, in general, suffer a degradation which is nondeterministic and statistical in character. Two important aspects of are, the mean target track relative to the source-sensor geometry, and the motional instabilities relative to the mean target track. The former creates an absolute upper bound on the useful coherence integration time which can be employed in the processor. The latter will depend on the spectral characteristics of the motional instabilities as well as the variance of the target course and speed. Results of the expected processor degradation are presented in both functional and graphical form for convenience in interpretation and data abstraction. An optimum integration time is derived from the standpoint of optimizing the processor gain for signal detection in an incoherent signal background. It is concluded that target motion can be the most serious deterrent to the use of coherent signal processors over exceptionally long integration intervals.