Platform for monitoring accuracy of on orbit cross calibration : Infrared Atmospheric Sounder onboard FY-3 satellite

For quantitative remote sensing, instrument calibration precision should be monitored from time to time. To monitor the accuracy of cross calibration of FY-3C satellite Infrared Atmospheric Sounder(IRAS), a platform was set up based on a cross comparison of IRAS with standard infrared high spectral resolution instruments- Infrared Atmospheric Sounding Interferometer (IASI). Calibration precision monitoring analysis using IRAS data in the year of 2014 shows results as the following. For all the 20 infrared channels the correlation coefficients of IRAS with IASI were above 0.98. The mean bias for most channels are less than 1K except that channels 9 and 16 are nearly 1.4 K and channels 1 and 18 are larger than 2 K. The standard deviation for most channels is less than 1.5 K, while for surface sounding bands of 8, 9, 18, 19, and 20, it ranges from 1.5 to 3 K. The latter is probably due to that the channels which detect atmosphere of near boundary layer were more susceptible to the time and location differences. The calibration bias variation trend with target brightness temperature was flat for channel 2, 3, 4, 10 to 13, while an obvious trend can be seen for channels of 14 to 20 and the difference between maximum bias and minimum bias can reach 5 K. Time series analysis of calibration bias indicates that for most channels the calibration bias were stable in one year and the variation magnitude was less than 0.3 K. It is about 1 K for channel 15, 19, and 20. The calibration bias variation reached 2 to 4 K in one year for channel 1, 14, 16, 17, 18. In a word, IRAS cross calibration accuracy monitoring system provide a tool for real time monitoring of calibration precision change.