Range Performance Modelling of Thermal Imaging System based on Single Parameter Characterised by Ambient Temperature and Relative Humidity

Range performance of a thermal imaging system is characterised by the prevailing atmospheric condition present at that time. There are two dominant parameters that limit the range performance of any thermal imaging systems i.e. ambient temperature and relative humidity. In the present work, comparative study of acquisition range performance of thermal imaging system operating in the long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) and spectral bands has been presented as a function of absolute humidity (AH) which is responsible for attenuation of IR radiation due to water vapour molecules present in path length. Presentation of acquisition range as function of AH leads to a single range performance table/graph for thermal imaging system under consideration for predefined visibility, target size, ambient temperature, target to background temperature difference and relative humidity. This table/graph can be used to predict detection, recognition and identification ranges for any set of combination of air temperature and relative humidity. The approach presented in this paper is versatile and has been illustrated through comparative performance analysis of LWIR and MWIR thermal imaging systems based on 640 x 512 staring focal plane array having identical design parameters in terms of resolution. It has been shown that MWIR performance is superior to LWIR beyond a crossover value of AH(T) even though MRTD of MWIR sensor is inferior to that of LWIR sensor at all spatial frequencies. Study has been carried out both for clear atmosphere and hazy conditions.