Correctability of the spatial nonuniformity in various infrared focal plane arrays

The correctability c characterizes the spatial noise of infrared focal plane arrays (FPA). This figure of merit indicates the ratio of the spatial to the temporal detector noise for a single or more frames. The goal of the correction procedure is to reduce the spatial noise to a magnitude below the temporal noise. In this case the correctability c is smaller than unity. In this paper we consider the transient degradation of the correctability after correction and define a novel characteristic number, the long-term stability time constant (tau) _lts. This time indicates operation duration subsequent to a nonuniformity correction after which the spatial noise increases to values higher than the temporal noise, i.e. for which the correctability reaches values larger than unity. Several staring infrared focal plane array detectors differing in array size and in detector material are investigated. The correctability c is determined after various correction procedures and the long-term stability time (tau) _lts is measured for each detector. The degradation of the correctability is caused by individual pixels in the detector array. We found that there are three different types of 'bad pixels,' which lead to a degradation of the correctability. Weak pixels having low or no responsivity as well as flickering and drifting pixels showing 1/f noise are classified.