# Radiometric Cross-Calibration of GF-1 PMS Sensor with a New BRDF Model
## 5 Discussion
### Results and Discussion of Time Series Cross-Calibration
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Date**} & \multicolumn{4}{c}{**OLI**} & \multicolumn{4}{c}{**MODIS**} \\ \cline{2-10}  & **Blue** & **Green** & **Red** & **NIR** & **Blue** & **Green** & **Red** & **NIR** \\ \hline Lab 1 & 0.2129 & 0.1688 & 0.1697 & 0.1748 & 0.2129 & 0.1688 & 0.1697 & 0.1748 \\ CRESDA 2 & 0.2247 & 0.1892 & 0.1889 & 0.1939 & 0.2247 & 0.1892 & 0.1889 & 0.1939 \\
24 February 2014 & 0.2278 & 0.1925 & 0.1872 & 0.2002 & 0.2239 & 0.1835 & 0.182 & 0.2013 \\
7 August 2014 & 0.2169 & 0.1807 & 0.1812 & 0.1912 & 0.2303 & 0.1976 & 0.1932 & 0.2031 \\
12 December 2014 & 0.2331 & 0.1924 & 0.1898 & 0.2127 & 0.2352 & 0.1916 & 0.1926 & 0.2192 \\
9 July 2015 & 0.2381 & 0.1988 & 0.1953 & 0.1999 & 0.2189 & 0.1885 & 0.1828 & 0.1883 \\
25 September 2015 & 0.2242 & 0.1889 & 0.1855 & 0.2024 & 0.2293 & 0.1841 & 0.1827 & 0.2103 \\
16 December 2015 & 0.2163 & 0.1816 & 0.1754 & 0.1990 & 0.2240 & 0.1724 & 0.1750 & 0.2073 \\
6 August 2016 & 0.2209 & 0.1814 & 0.1797 & 0.1923 & 0.2315 & 0.1949 & 0.1932 & 0.2078 \\ \hline \hline \end{tabular}  
* \({}^{1}\) Lab’ represents the calibration coefficients obtained in laboratory conditions. 2 \({}^{2}\) ‘CRESDA’ represents the official calibration coefficients by site calibration method.  
\end{table} 
Table 10: Laboratory calibration coefficients, CRESDA site calibration coefficients and cross-calibration coefficients calculated in this paper. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Site**} & \multirow{2}{*}{**Date**} & \multicolumn{4}{c}{**OLI**} & \multicolumn{4}{c}{**MODIS**} \\ \cline{3-10}  & & **Blue** & **Green** & **Red** & **NIR** & **Blue** & **Green** & **Red** & **NIR** \\ \hline \multirow{3}{*}{Dunhuang} & 7 August 2014 & \(3.47\%\) & \(4.48\%\) & \(4.08\%\) & \(1.40\%\) & \(-2.47\%\) & \(-4.43\%\) & \(-2.26\%\) & \(-4.76\%\) \\  & 6 August 2016 & \(1.69\%\) & \(4.13\%\) & \(4.85\%\) & \(0.82\%\) & \(-3.03\%\) & \(-3.01\%\) & \(-2.28\%\) & \(-7.17\%\) \\  & 9 July 2015 & \(-5.96\%\) & \(-5.05\%\) & \(-3.40\%\) & \(-3.08\%\) & \(2.58\%\) & \(0.37\%\) & \(3.23\%\) & \(2.89\%\) \\ \hline \multirow{3}{*}{Golmud} & 24 February 2014 & \(-1.38\%\) & \(-1.72\%\) & \(0.89\%\) & \(-3.24\%\) & \(0.36\%\) & \(3.04\%\) & \(3.64\%\) & \(-3.88\%\) \\  & 12 December 2014 & \(-3.74\%\) & \(-1.69\%\) & \(-0.48\%\) & \(-9.67\%\) & \(-4.69\%\) & \(-1.29\%\) & \(-1.98\%\) & \(-13.05\%\) \\ \cline{1-1}  & 25 September 2015 & \(0.23\%\) & \(0.15\%\) & \(1.82\%\) & \(-4.40\%\) & \(-2.07\%\) & \(2.70\%\) & \(3.27\%\) & \(-8.44\%\) \\ \cline{1-1}  & 16 December 2015 & \(3.76\%\) & \(4.00\%\) & \(7.17\%\) & \(-2.61\%\) & \(0.31\%\) & \(8.88\%\) & \(7.36\%\) & \(-6.90\%\) \\ \hline \hline \end{tabular}  
* \({}^{1}\) Lab’ represents the calibration coefficients obtained in laboratory conditions. 2 \({}^{2}\) ‘CRESDA’ represents the official calibration coefficients by site calibration method.  
\end{table} 
Table 11: The relative errors between cross-calibration coefficients and CRESDA site calibration coefficients.