Calculation Of Operating Range To The Infrared Detection System Under Different Atmospheric Conditions

In recent years,the infrared detection technology has got rapid development,for its superior characteristics,now it has been widely used in many fields of military and civil affairs.The operating range of infrared detection system is one of the important parameters to evaluate the performance of infrared detection system,so it is important to estimate it.The main influencing factors of operating range to the infrared detection system are as follows: infrared radiation characteristics of target and background,atmospheric attenuation of infrared radiation and the performance of infrared system.For the complexity of atmospheric environment and the selective absorption of atmospheric molecules,which made the atmospheric transmittance a complex quantity.The spectral detectivity is a representative parameter to characterize the detector performance which relate to the spectral responsivity and noise of detector.In this paper the theoretical calculation model of operating range of the infrared detection system is established which based on radiation metrology and the basic principle of infrared detection system.With the problem of spectral detectivity,the expression of spectral detectivity of photoconductive detector is derived from the response characteristics and main noise mechanism of photocondutive detector.The spectral detectivity of HgCdTe detector is calculated with the different working temperature and different background field.Aiming at the problem of atmospheric transmittance,calculating the atmospheric transmittance with MODTRAN software on the atmospheric composition,altitude,season,geographical dimensions,the weather and so on,and analyzing the reasons of changes of the atmospheric transmittance between 3~5 ?m and 8~13?m.In order to make the atmospheric transmittance calculated by MODTRAN can be combined with the theoretical model,the spectral bands are divided into many small bands before using MODTRAN to calculate the atmospheric transmittance of each band,at the same time the corresponding atmospheric transmittance database is established.Because of SNR associated with the detection probability,the function of SNR is established with ORIGIN on the detection probability.Based on the function of SNR and the spectral detectivity model,the original model of operating range is modified and improved by spectral bisection method,so the integral shape of the model is transformed into a summation form.A case study of Catherin-FC thermal imager shows that the improved model has a certain degree of accuracy.At last,factors such as detecting height,area,season,relative humidity,rain,fog,zenith angle,the height of search and cloud weather are taken into consideration for calculating the changes in the operating range of infrared system.