Instrument simulator and independent calibration approach for infrared sounder onboard the SI-traceable satellite

Abstract

The infrared sounder (IRS) of Chinese Spaced-based Radiometric Benchmark (CSRB) mission is an infrared spectrometer designed to demonstrate measurement of SI-traceable spectrally resolved infrared (IR) radiances from orbit with extremely high absolute radiometric accuracy (better than 0.1 K 2-σ or k=2 brightness temperature at scene temperature). The major objectives of this sounder are to observe high-accuracy, long-term climate change trends and to intercalibrate the international operational IR sensors to similar measurement accuracy. The improvement of absolute accuracy is achieved through an Independent Calibration System, which employs phase change cells to establish an on-orbit temperature scale and enables the observations to be traced to the Système Internationale (SI) standard for Kelvin. The principle of this system is similar to that used in metrological laboratories for temperature calibration using phase changes of pure materials as these are extremely reproducible and have well characterized temperatures that can be unequivocally traceable to the 1990 International Temperature Scale (ITS-90). In addition to the onboard calibrator (blackbodies for IRS) used to provide stable on-orbit calibration, the design of the instrument is also crucial for achieving traceable measurements. During the design phase, the instrument should be well characterized and calibrated at subsystem and/or component level, and ultimately develop an instrument traceability chain to identify all calibration effects. The instrument calibration model is defined, and all uncertainty effects contributing to the calibrated Level-1 data are traced through to their original sources. In such a context, this paper presents the development of an end-to-end Simulator of IRS (SIRS) for error analysis and calibration approach deriving. Conceived as the numerical abstraction of the physical instrument, SIRS encapsulates optical physics and empirical results gained from laboratory analysis, and ultimately yields a robust mathematical framework and proxy data source for the IRS calibration.