The effects of electronic microscanning on infrared image aliasing and spaial resolution

Abstract

Most modern infrared electro-optical imaging systems utilize staring imagers to acquire image data. Typical staring focal plane arrays contain a two-dimensional array of photodetectors. Each photodetector generates an electrical current or charge proportional to the number of photons striking its immediate vicinity. However, due to the discrete finite nature of the FPA detector lattice and fact that each photodetector's collection area is matched to the optical blur for signal to noise considerations, the imager does not satisfy the Nyquist criteria for sampling systems. Consequently, aliasing effects are usually an inherent part of images produced by staring arrays. Microscanning is a method which can be used to reduce spatial frequency aliasing within an image by spatially oversampling the image scene. During the microscanning process, several optically dithered subimages are acquired and combined to create a larger image. The resulting image will have a higher sampling rate, and accordingly a greater Nyquist cutoff frequency, with the same spatial frequency resolution and optical cutoff frequency. This thesis discusses the effects of a novel approach to the microscanning operation, called electronic microscanning. The electronic microscanning device performs the microscan operation by shifting the collection area of each pixel in the array by half-pixel increments instead of utilizing mechanical or liquid crystal filters to deflect the image. Electronic microscanning has an inherent advantage over traditional microscanning systems since no scanners or moving parts are needed to oversample the image. A model of the electronic microscan device is developed and compared to prototype laboratory results obtained at the Raytheon Company Electro-Optics Laboratory in Tewksbury, Massachusetts.