A twin-channel difference model for cross-calibration of thermal infrared band

Based on the conduction and transformation of the thermal infrared radiative transfer equation of water target, a twin-channel difference model (DM) was proposed to improve the calibration precision by conquering the limitation that the atmospheric condition when image is acquiring cannot be truly obtained in the traditional radiometric simulation calibration method. The analysis of surface, atmosphere and top-of-atmosphere (TOA) radiative energy decomposition demonstrated that the apparent TOA radiance of the uncalibrated channel is the differential combination of two reference channels. The DM avoids impacts from atmospheric temperature and density. The only impact is from water vapor (WV) content. Based on the fitting error analysis of 742 mid-latitude atmospheric profiles (column WV content: 0–5×103 atm cm) selected from TIGR database, the DM is insensitive to WV content. The maximum error is less than 0.2 K when the view zenith angels (VZAs) of reference channels and uncalibrated channel are less than 30°. The error becomes 0.3 K when VZAs range from 30° to 40° and 0.6 K when VZAs are in 40°–50°. Because the uncertainty increases when VZAs are larger than 50°, the best range of VZAs is 30°–50°. The vicarious calibration results at Lake Qinghai field indicated that the calibration precision of the DM cross-calibration by using MODIS bands 31 and 32 as reference channels to calibrate IRS band 08 is similar to that of vicarious calibration. Therefore, the DM is a reliable alternative tool for sensor on-orbit calibration and validation with high precision and frequency.