# Evaluation on Radiometric Capability of Chinese Optical Satellite Sensors
## 3 Results and Discussion
### Radiometric Capability Evaluation of Feng Yun 3/Medium-Resolution Spectral Imager (FY-3/Merssi)  
The same plots of the FY-3/MERSIs as the MODISs are presented in Figure 9. The temporal range of FY-3A/MERSI is 2008-2015 and that of FY-3B/MERSI is 2010-2015. The radiometric characteristics of the MERSIs are as follows:  
1. The stability of FY-3A/MERSI is very good at all times except the duration from February to December of 2012, when a strongly increasing trend occurred. Although calibration coefficients have been updated four times, the variation of the TOA reflectance remains consistent. The reasons inducing the abnormal increasing within stage 3 is unknown and we surmise that it may be caused by an instrument malfunction. After it was found by the surveillance department, a manual adjustment was made and the instrument suddenly became normal. The statistics for FY-3A/MERSI are calculated, excluding the instrument malfunction duration, and listed in Table 12. The slope values of the fitted lines for different bands are at the 10\({}^{-5}\) level, which indicates a very small variation trending. The highest variation of TOA reflectance occurs in the blue band, up to 62.72%. The variations of the other three bands are 33.74%, 24.86%, and 25.52% respectively. The differences in four bands between the mean TOA reflectance after spectral matching and corresponding bands of MODIS are all less than 0.015. All the standard deviations \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sensor**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Band**} & \multirow{2}{*}{**Slope**} & \multirow{2}{*}{**Maximum**} & \multirow{2}{*}{**Minimum**} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**Mean\_a**} & \multirow{2}{*}{\begin{tabular}{c} **Mean\_a** \\ **Mean\_M** \# \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Mean\_a** \\ **Mean\_M** \# \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} } \\ \hline \multirow{8}{*}{HJ-IB/CCD1} & \multirow{8}{*}{2009} & Blue & \(1.80\times 10^{-5}\) & 0.1614 & 0.1378 & 0.1499 & 0.1773 & 0.0373 & 0.0072 \\  & Green & \(4.06\times 10^{-5}\) & 0.1842 & 0.1625 & 0.1730 & 0.1883 & 0.0223 & 0.0066 \\  & Red & \(2.74\times 10^{-5}\) & 0.2314 & 0.2096 & 0.2208 & 0.2240 & 0.0010 & 0.0070 \\  & NIR & \(1.16\times 10^{-5}\) & 0.2608 & 0.2353 & 0.2489 & 0.2492 & \(-0.0248\) & 0.0084 \\ \cline{2-10}  & \multirow{8}{*}{2010} & Blue & \(-\) & 0.1874 & 0.1572 & 0.1694 & 0.2003 & 0.0603 & 0.0087 \\  & Green & \(4.80\times 10^{-5}\) & 0.1954 & 0.1730 & 0.1848 & 0.2012 & 0.0352 & 0.0061 \\  & Red & \(5.34\times 10^{-5}\) & 0.2400 & 0.2112 & 0.2248 & 0.2281 & 0.0051 & 0.0068 \\  & NIR & \(3.88\times 10^{-5}\) & 0.2657 & 0.2258 & 0.2459 & 0.2462 & \(-0.0278\) & 0.0108 \\ \cline{2-10}  & \multirow{8}{*}{2011} & Blue & \(-\) & 0.2004 & 0.1546 & 0.1700 & 0.2010 & 0.0610 & 0.0140 \\  & Green & \(-\) & 0.2069 & 0.1756 & 0.1889 & 0.2056 & 0.0396 & 0.0099 \\  & Red & \(-\) & 0.2572 & 0.2174 & 0.2321 & 0.2355 & 0.0125 & 0.0120 \\  & NIR & \(-\) & 0.2847 & 0.2281 & 0.2523 & 0.2526 & \(-0.0214\) & 0.0158 \\ \cline{2-10}  & \multirow{8}{*}{2012} & Blue & \(-\)/\(7.65\times 10^{-5}\) & 0.2004 & 0.1576 & 0.1669 & 0.1974 & 0.0574 & 0.0075 \\  & Green & \(-\)8.14 \(\times 10^{-5}\) & 0.2097 & 0.1903 & 0.1988 & 0.2164 & 0.0504 & 0.0069 \\ \cline{2-10}  & \multirow{8}{*}{2012} & Red & \(-\)/\(8.48\times 10^{-5}\) & 0.2572 & 0.2293 & 0.2428 & 0.2464 & 0.0234 & 0.0076 \\ \cline{2-10}  & & NIR & \(-\)1.25 \(\times 10^{-5}\) & 0.2900 & 0.2537 & 0.2741 & 0.2744 & 0.0004 & 0.0113 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: The statistics from the time series of the TOA reflectances of HJ-1B/CCD1. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sensor**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Band**} & \multirow{2}{*}{**Slope**} & \multirow{2}{*}{**Maximum**} & \multirow{2}{*}{**Minimum**} & \multirow{2}{*}{**Mean**} & \multirow{2}{*}{**Mean\_a**} & \multirow{2}{*}{\