Optical EngineeringImagery improvements in staring infrared imagers by employing subpixel microscan
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Imagers based on focal plane arrays (FPAs) risk introducing in-band and out-of-band spurious responses, or aliasing, due to undersampling. IR systems can use microscan (or dither) to reduce aliasing. We describe a generic microscan technique and the benefits of microscanning, including an analysis of and experiments on four-point microscan employed in IR imagers, in which the image is mechanically shifted by 1/2 pixel between fields, in each dimension. Our purpose is to describe the benefits of microscanning for IR systems employing sensitive detectors. Through analysis and experiments on production systems, we show that microscanning is an effective way to improve the resolution of imaging systems. In addition, we present experimental data that shows that this increased resolution results in lower minimum resolvable temperatures (MRTs) than an equivalent nonmicroscanned system; and that this improvement in MRT is accompanied by an increase in detection, recognition, and identification (DRI) range performance in a real-world system. The microscan hardware can also be used to null out residual gimbal jitter in a stabilized imaging system, resulting in a jitter reduction of 35 to 50%. We show that this technique, known as microscan stabilization (MSS), is complementary to microscan, and further increases the imaging system performance.