Laboratory testing of dithered infrared imaging systems

摘要

This paper addresses the problem of determining the amount of aliasing reduction achieved in a dithered infrared imaging system. Usually the elements of an infrared focal plane array (IRFPA) stare at fixed positions in space. Without scanning, the scene is unavoidably undersampled as long as the optical blur spot is smaller than the IRFPA elements. To increase the sampling rate, the scene can be optically dithered to allow the image to be augmented by an additional set of samples offset relative to the initial set by half the width of the detector elements. This technique is commonly referred to as microscanning. There is a need for laboratory test procedures with which to ascertain the effectiveness of the dithering technique. This paper describes a technique for determining the effectiveness of aliasing reduction through analysis of images collected using a canted unresolved slit. The procedure uses the 2D fast Fourier transform (FFT). The baseband component of the FFT yields information on the system MTF, whereas the component centered about the sampling frequency reveals the amount of aliasing. The analysis yields an estimate of the dither positioning error, where the maximum error corresponds to mere pixel replication with no effective aliasing reduction. The approach demonstrates a technique for objective assessment of imaging IR performance that has application in acceptance testing procedures.