# Radiometric Cross-Calibration of GF-1 PMS Sensor with a New BRDF Model
## 4 Results
### Validation of Radiometric Cross-Calibration
#### 4.2.2 Consistency Analysis of Calibration Results Using Different Reference Satellites  
Table 4 shows the results of cross-calibration of GF-1 satellite PMS1 sensor using MODIS and Landsat 8 OLI as reference sensors, respectively. The relative errors (1-cross-calibration coefficient using Landsat 8 OLI as a reference/cross-calibration coefficient using MODIS as a reference) of cross-calibration coefficients between the two reference sensors are calculated. As can be seen from Table 4, the absolute value of relative error of the Golmud calibration test site is less than that of the Dunhuang calibration test site. At the Dunhuang test site, the relative errors of cross-calibration coefficients between the two reference sensors are 5.80%, 8.53%, 6.20%, and 5.87%, while at the Golmud site, the relative errors are \(-\)1.08%, \(-\)2.66%, \(-\)3.17%, and \(-\)1.47%, respectively, which means that whether at the Dunhuang or Golmud test site, the cross-calibration results using the two reference satellites are in good agreement, especially at the Golmud site. The results demonstrate that the  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference Sensor** & **Site** & **Blue** & **Green** & **Red** & **NIR** \\ \hline OLI & (1-D \({}^{1}\)/G \({}^{2}\)) [3] & 4.78\% & 6.10\% & 3.22\% & 4.49\% \\ MODIS & 1-D/G & \(-\)2.84\% & \(-\)7.70\% & \(-\)6.12\% & \(-\)0.89\% \\ \hline \end{tabular} \({}^{1}\) D\({}^{\prime}\) represents the Dunhuang site. \({}^{2}\) G\({}^{\prime}\) represents the Golmud site. \({}^{3}\) \({}^{1}\)-D/G\({}^{\prime}\) represents the relative error of cross-calibration coefficients between Dunhuang and Golmud site.  
\end{table}
Table 6: The relative error of cross-calibration coefficients between Dunhuang and Golmud sites using Landsat 8 OLI and MODIS sensor as a reference.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**BRDF Correction** & **Site** & **Refer Sensor** & **Blue** & **Green** & **Red** & **NIR** \\ \hline \multirow{4}{*}{Without BRDF correction} & \multirow{4}{*}{Dunhuang} & CRESDA [1] & 0.2247 & 0.1892 & 0.1889 & 0.1939 \\  & & 1-L \({}^{2}\)/SC & 1.29\% & 5.50\% & 7.41\% & 5.36\% \\  & & (1-M \({}^{3}\)/SC) [4] & 14.06\% & 10.99\% & 10.85\% & 4.59\% \\ \cline{2-6}  & \multirow{2}{*}{Golmud} & 1-L/SC & \(-\)2.67\% & \(-\)2.91\% & \(-\)0.37\% & \(-\)3.71\% \\  & & 1-M/SC & \(-\)12.02\% & \(-\)7.29\% & \(-\)0.69\% & \(-\)7.84\% \\ \hline \multirow{4}{*}{With BRDF correction} & \multirow{2}{*}{Dunhuang} & 1-L/SC & 3.47\% & 4.48\% & 4.08\% & 1.40\% \\  & & 1-M/SC & \(-\)2.47\% & \(-\)4.43\% & \(-\)2.26\% & \(-\)4.76\% \\ \cline{2-6}  & \multirow{2}{*}{Golmud} & 1-L/SC & \(-\)1.38\% & \(-\)1.72\% & 0.89\% & \(-\)3.24\% \\ \cline{1-1}  & & 1-M/SC & 0.36\% & 3.04\% & 3.64\% & \(-\)3.83\% \\ \hline \end{tabular} \({}^{1}\) *CRESDA’ represents the official calibration coefficients by site calibration method. \({}^{2}\) L\({}^{\prime}\) represents the cross-calibration coefficients by using Landsat 8 OLI sensor. \({}^{3}\) M\({}^{\prime}\) represents the cross-calibration coefficients by using the MODIS sensor. \({}^{4}\) 1-M/SC represents the relative error between cross-calibration coefficients by using MODIS sensor and site calibration coefficients.  
\end{table}
Table 5: Site calibration coefficients and the relative error between cross-calibration coefficients and site calibration coefficients.  
BRDF-corrected large observation angle MODIS images can be used as reference data for remote sensing radiometric cross-calibration.