Absolute Radiometric Calibration of Earth Radiation Measurement on FY-3B and Its Comparison With CERES/Aqua Data

摘要

The Earth Radiation Measurement (ERM) instrument onboard FengYun (FY)-3B satellite observes the Earth's atmosphere through a narrow scanning field of view (NFOV) and a wide nonscanning FOV. For each field of view, the measurements are made from two broadband channels: a total waveband channel covering 0.2–50 $muhbox{m}$ and a shortwave (SW) band covering 0.2–4.3 $muhbox{m}$. The validation to the ERM calibration was carried out by comparing the unfiltered longwave (LW) and SW radiances from ERM with those from Clouds and Earth's Radiation Energy System (CERES) flight model 3 onboard Earth Observing System Aqua satellite. While the ERM LW and SW radiances have a good correlation with CERES data, there is a systemic bias between the two data sets. A spectral correction is made for the ERM data using the CERES data. After the correction, the error of the ERM LW radiance is reduced from $-$3.00 to $-0.60 hbox{W/sr} cdot hbox{m}^{2}$. For the SW radiance, the bias is reduced from 6.00 to 4.00 $hbox{W/sr} cdot hbox{m}^{2}$. Based on the ERM in-orbit calibration data, the stability of the ERM LW radiometric response is analyzed, and it is shown that the gains are stable with a variation of less than 1.5% during its first 9 months in orbit. However, the gains at the SW channels have larger changes and exceed 3%. These drifts might be caused by the detector degradation. Also, the NFOV scanner at the SW channel is no longer working after its 8 months in orbit.