# Radiometric Cross-Calibration of GF-1 PMS Sensor with a New BRDF Model
## 4 Results  
### Cross-Calibration Results Based on the BRDF Model  
According to the proposed BRDF model and cross-calibration method proposed in this paper, the radiometric calibration coefficients of the GF-1 satellite PMS1 sensor with BRDF correction over Dunhuang and Golmud test sites were calculated. Meanwhile, the cross-calibration coefficients without BRDF correction were also calculated for comparison. Table 4 illustrates the BRDF correction coefficients (COE\({}_{BRDF}\)), cross-calibration coefficients with and without BRDF correction at Dunhuang and Golmud test sites by using Landsat 8 OLI sensor and MODIS sensor, and the relative error of cross-calibration coefficients between the two sensors. The relative error is defined as \"1-cross-calibration coefficient by using Landsat 8 OLI sensor/cross-calibration coefficient by using MODIS sensor\".  
The site calibration coefficients and the relative error between cross-calibration coefficients with and without BRDF correction by using Landsat 8 OLI sensor and MODIS sensor and site calibration coefficients is exhibited in Table 5. The relative error is defined as \"1-cross-calibration coefficient/site calibration coefficient\".  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Type** & **Site** & **Refer Sensor** & **Blue** & **Green** & **Red** & **NIR** \\ \hline \multirow{4}{*}{(COE\({}_{BRDF}\))4} & Dunhuang & L8 OLI(L 1) & 1.0004 & 1.0238 & 1.0266 & 1.0186 \\  & & MODIS(M 2) & 1.0440 & 1.1065 & 1.1096 & 1.0818 \\ \cline{2-7}  & Golmud & L8 OLI(L) & 1.0011 & 1.0017 & 1.0015 & 1.0011 \\  & & MODIS(M) & 0.7213 & 0.8025 & 0.8494 & 0.8609 \\ \hline \multirow{4}{*}{With BRDF correction} & Dunhuang & L8 OLI(L) & 0.2169 & 0.1807 & 0.1812 & 0.1912 \\  & Dunhuang & MODIS(M) & 0.2303 & 0.1976 & 0.1932 & 0.2031 \\  & & (1-L/M) 3 & 5.80\% & 8.53\% & 6.20\% & 5.87\% \\ \cline{2-7}  & & L8 OLI(L) & 0.2278 & 0.1925 & 0.1872 & 0.2002 \\  & [PERSON] & MODIS(M) & 0.2239 & 0.1835 & 0.182 & 0.2013 \\  & & 1-L/M & \(-1.08\%\) & \(-2.66\%\) & \(-3.17\%\) & \(-1.47\%\) \\ \hline \multirow{4}{*}{Without BRDF correction} & [PERSON] & L8 OLI(L) & 0.2218 & 0.1788 & 0.1749 & 0.1835 \\  & [PERSON] & MODIS(M) & 0.1931 & 0.1684 & 0.1684 & 0.185 \\ \cline{1-1}  & & 1-L/M & \(-14.86\%\) & \(-6.18\%\) & \(-3.86\%\) & 0.81\% \\ \cline{1-1} \cline{2-7}  & & L8 OLI(L) & 0.2307 & 0.1947 & 0.1896 & 0.2011 \\ \cline{1-1}  & Golmud & MODIS(M) & 0.2517 & 0.203 & 0.1902 & 0.2091 \\ \cline{1-1}  & & 1-L/M & 8.34\% & 4.09\% & 0.32\% & 3.83\% \\ \hline \end{tabular}  
* 1 \(\mathrm{\AA}\)’ represents the Landsat 8 OLI sensor. 2 \(\mathrm{\AA}\)’ represents the MODIS sensor. 3 \(\mathrm{\AA}\)’1-L/M’ represents the relative error between cross-calibration coefficients by using Landsat 8 OLI sensor and cross-calibration coefficients by using MODIS sensor. 4 \(\mathrm{COE}_{BRDF}\)’ represents the BRDF correction coefficients.  
\end{table}
Table 4: BRDF correction coefficients, radiometric cross-calibration coefficients with and without BRDF correction at Dunhuang and Golmud test sites by using Landsat 8 OLI sensor and MODIS sensor, and the relative error of cross-calibration coefficients between the two sensors.