Microscan in infrared staring systems

Abstract

Sampling-limited resolution in a two-dimensional infrared focal plane array is discussed in terms of the reciprocal (inverse) lattice in the frequency domain. It is shown how the bandwidth of the signal that can be reconstructed without error can be increased by a microscan. Microscanning means translating the image over the detector array along a short distance and then resampling the image, thus increasing the spatial sampling rate by decreasing the distance between samples. Two current microscan modes are compared: the rectangular bidirectional mode, in which the image is translated by half the array’s pitch along the two main perpendicular axes, and the diagonal mode, in which the image is shifted by half the diagonal of a rectangle defined by four adjacent pixels. It is shown that the diagonal mode implies the same frequency limit in accordance with the Nyquist criterion, in the horizontal and vertical directions, as the bidirectional mode. The temporal MTF that is a result of the microscan is calculated for the case where the temporal impulse response is a one-sided exponential pulse, like the thermal response of uncooled IR detectors. A simple algorithm for the reconstruction of the diagonal-microscan sampled data is suggested, and its MTF is derived.