Modeling noise in thermal imaging systems

Noise must always be considered in predicting the performance of a thermal imaging system. The optimum sensitivity of such a system is achieved when the system is `background noise limited' -- that is, when the predominant source of noise is that associated with the random arrival of photons onto the infrared detector. In the absence of other noise sources, the fluctuation in the detector output has a white noise spectrum which is then modified by sampling, filtering, digitizing, or whatever other signal processing is applied. When other significant noise sources exist, their effect on the output noise spectrum must be properly analyzed if sensor performance is to be adequately estimated. This paper discusses several excess noise sources and explains how to combine these sources with background noise. The principal emphasis is on scanning sensors using second-generation detector arrays, commonly referred to as `focal plane arrays.' Excess noise sources considered include 1/f noise, digitization noise and several types of fixed pattern noise as well as white noise associated with signal amplification. The effects of the resultant total noise spectrum on both NETD and MRTD are analyzed.