Impact of speckle on laser range-gated shortwave infrared imaging system target identification performance

The U.S. Army and the U.S. Air Force are investigating laser range-gated shortwave infrared (LRG-SWIR) imaging systems for use in target identification. When coupled to an electro-bombarded CCD, the imaging system can obtain high-resolution images at long ranges. Speckle, an image artifact inherent in laser illuminated imaging systems, results from interference patterns caused by the coherent illumination. Laser speckle degrades target identification performance but can be reduced by averaging successive LRG-SWIR images. This research is a first attempt at quantifying target identification performance degradation associated with laser speckle. The research begins with a laboratory experiment to verify a speckle model that includes power spectral density and intensity probability density functions. An LRG-SWIR sensor simulation is developed that includes coherent illumination resulting in speckle target images. A field demonstration is performed to verify the fidelity of the simulation. The simulation is then applied to the NVESD target identification set with various levels of image averaging and blur. Observer performance results are analyzed in terms of target identification probability and the effects of various levels of blur and speckle are characterized.