## 3 Results
### Determination of DN to Radiance Coefficients for KOMPSAT-3 and -3A  
Finally, in this study, we updated the DN of the radiance coefficients of KOMPSAT-3 and -3A in light of the changed TDI adjustment of the payload CCD specification for KOMPSAT-3A and of the fact that sensor degradation over time is expected, especially for KOMPSAT-3. Table 4 shows the estimated radiometric calibration coefficients (scale) and offsets from intensive field campaigns during 2017. In the case of KOMPSAT-3A, although only one scale factor was estimated, despite several field observations, the geometric and atmospheric conditions in Tables 2 and 3 are valid for determining DN to satellite radiance coefficients. The viewing zenith angle of KOMPSAT-3A acquired on 19 September 2017 is \(3.112^{\circ}\), meaning that a negligible BRDF effect is expected because the geometric difference between ASD and KOMPSAT-3A is less than \(5^{\circ}\). Figure 9 shows the scatterplots between KOMPSAT-3A DN and TOA radiance from the 6S radiative transfer model for four multispectral bands. The scatter plots of TOA radiance calculated from four distinctive radiometric tarps and the KOMPSAT-3A DN values are closely located along the lines of linear regression in each spectral band. Additionally, the coefficient of determination (R\({}^{2}\)) values all exceed 0.999, indicating that the suggested methods are suitable for determining DN to radiance coefficients. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Band**} & \multicolumn{4}{c}{**Scale Factor**} \\ \cline{2-5}  & **KOMPSAT-3, 05/14** & **KOMPSAT-3, 07/27** & **KOMPSAT-3A, 09/19** & **KOMPSAT-3, 09/20** \\ \hline Blue & \(0.0256\) (0.0260) 1 ** & \(0.0239\) & \(0.0362\) & \(0.0275\) \\ Green & \(0.0359\) (0.0365) 1  & \(0.0309\) & \(0.0249\) & \(0.0382\) \\ Red & \(0.0259\) (0.0265) 1  & \(0.0230\) & \(0.0229\) & \(0.0294\) \\ NIR & \(0.0177\) (0.0181) 1  & \(0.0149\) & \(0.0130\) & \(0.0192\) \\ \hline \hline \multicolumn{5}{c}{**Offset**} \\ \hline Blue & \(-47.8711\) (\(-48.7996\)) 1  & \(-45.0553\) & \(-22.1416\) & \(-28.4989\) \\ Green & \(-38.8875\) (\(-40.5952\)) 1  & \(-24.9649\) & \(-14.0210\) & \(-27.3846\) \\ Red & \(-21.5454\) (\(-21.6730\)) 1  & \(-14.8416\) & \(-13.0457\) & \(-21.6854\) \\ NIR & \(-20.5972\) (\(-20.2303\)) 1  & \(-14.2401\) & \(-10.2834\) & \(-13.5910\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Updated DN to radiance coefficients and offsets for KOMPSAT-3 and -3A based on vicarious calibration methods using radiometric tarps and Microtops II in 2014. Figure 9: _Cont._In the case of KOMPSAT-3, however, three cases of scale factors were estimated by performing field campaigns during the study period due to benign weather conditions. However, comparing each scale factor in Table 4 shows that these are non-negligibly different values, which would cause a substantial TOA radiance error despite using the same KOMPSAT-3 data. The major reason for the scale factor difference is likely the large viewing zenith angles of KOMPSAT-3 because the greater the tilt of the satellite zenith angle, the more substantial the BRDF effect of the surface radiometric tarps. The last field campaign of KOMPSAT-3 at the Zuummod site in Mongolia (Table 4), acquired on 18 June 2015 exhibits the best results because the viewing zenith angle of the satellite is similar to the nadir direction of ASD Fieldspec(r) 3. Figure 10 shows the scatterplots between KOMPSAT-3 DN and simulated TOA radiance for all multispectral bands acquired on 20 September 2017. Through this relationship, the scale factor of the last column of Table 4 is determined as the KOMPSAT-3 DN to radiance coefficients for four multispectral bands. All the dots between TOA radiance and KOMPSAT-3 for four distinctive radiometric tarps are closely located over the linear least-square fit lines. Additionally, the R\({}^{2}\) values for all spectral bands are 0.999, indicating that the determined scale factors are reasonable for converting DN to radiance with reliable accuracy.