The impacts of temperature and emissivity estimations on radiance-based calibration for HJ-1B/IRS TIR band

The IRS radiometer on the HJ-1B satellite of HJ-1 constellation has just a wide band (IRS B08) in thermal infrared spectral region between 10 and 12 μm. The onboard radiometric calibration of IRS B08 is implemented by periodically heating the blackbody of calibration system from normal temperature status (NTS) to high temperature status (HTS) for the lack of observation to deep space. Radiance-based vicarious calibration was taken as one point in two-point calibration method to substitute NTS for the instability of NTS. The estimation impacts of temperature and emissivity were analyzed by defining band matching factor k. The results indicate that their impacts were related to channel center wavelengths of reference and target bands. As to the reference band of CE312 B02, temperature impact of ±10 K estimated error on IRS B08 TOA radiance can be ignored while six substituted emissivities demonstrated their impacts can also be ignored. However, if CE312 B03 or B04 was taken as reference bands, the impacts cannot be ignored even emissivity-specimens of fresh water, sea water and blackbody were used as actual surface. Linear combination of two reference bands surrounding target band, such as CE312 B03 and B04 to IRS B08, significantly reduced the calibration uncertainty of using single reference band from 1.8 K and 2.5 K to 0.4 K. The vicarious calibration accuracy based on CE312 B02 is 0.25 K and the vicarious calibration coefficients could be used from August 2009 to August 2010.