<title>Coherence-based optical detection system's receiver operating characteristics (ROC) curves</title>

Abstract

High detection probabilities with low false alarm rates, even in the presence of as much as - 28 dB signal to clutter can be obtained, if use is made of the coherence information contained in the input signal. Such a detection system is described and its Receiver Operating Curves (ROC) characterized from a reduced experimental set of data. The system has an input filter with a rectangular passband, an interferometer and a photodetector. The filter gives rise to a sinc function shaped interferogram envelope in optical path difference. The position of the interferogram's first null depends on the effective bandwidth of the scene in the instrument's field of view. The detection system is sensitive to the degree of coherence of the scene. The amount of the shift of the position of the first null is found to be a highly sensitive measure of the presence of a very narrow-band target within the instrument's input bandpass filter. An important characteristic of this system is that the shift is still detected even when an intense wideband incoherent source, which may be considered to be clutter, is introduced into the input. We measured the ROC curves for the optical detection system using a He-Ne laser narrowband coherent source target with a tungsten halogen bulb wideband incoherent background clutter. We show that the target source can be detected even when it is substantially weaker than the clutter at - 28 dB signal to clutter. We compare the predictions of our theoretical model with the experimental results and show good agreement.