## 2 Materials and Methods  
The characteristics of high-resolution optical satellites include a narrow field of view (FOV) and a long revisit time. Therefore, it is difficult to perform radiometric calibration with a high temporal frequency using natural targets such as deep convection clouds, the deep ocean, or bright deserts. On the contrary, a field campaign using artificial reference targets, typically tarps, can be a useful way to calibrate a high-resolution satellite sensor. In this study, vicarious radiometric calibrations of KOMPSAT-3 and -3A multispectral imaging sensors were performed using radiometric tarps and atmospheric measurements. Table 1 shows detailed specifications of the KOMPSAT-3 and -3A sensors, where the main difference between the satellites is their spatial resolution and the presence of IR channels mounted on KOMPSAT-3A. Although the detailed sensor specifications are slightly different, the multispectral bands of the Advanced Earth Image Sensor System (AEISS) and AEISS-A, mounted on KOMPSAT-3 and -3A, respectively, have the same spectral response functions (SRF) and practical spectral ranges as the bands affected by atmospheric constituents and the surface. Therefore, the same algorithm was used for the vicarious radiometric calibration of each satellite sensor using the radiative transfer model. We selected three different field campaign sites: Goheung in South Korea (34.60\({}^{\circ}\)N, 127.20\({}^{\circ}\)E), Naju in South Korea (35.10\({}^{\circ}\)N, 126.82\({}^{\circ}\)E), and Zuunmod in Mongolia (47.72\({}^{\circ}\)N, 106.96\({}^{\circ}\)E). Figure 1 shows images of the study area for each field campaign site; the left column shows the RGB images \begin{table}
\begin{tabular}{c c c} \hline \hline
**Mission Characteristic** & **KOMPSAT-3** & **KOMPSAT-3A** \\ \hline Design lifetime & 4 years & 4 years \\ \hline Orbit altitude & 685 km & 528 km \\ \hline Swath width & \(\geq\)15 km (at nadir) & \(\geq\)12 km (at nadir) \\ \hline \multirow{3}{*}{Ground sample distance} & Pan: 0.7 m (altitude 685 km) & Pan: 0.55 m (altitude 528 km) \\  & MS: 2.8 m (altitude 685 km) & MS: 2.2 m (altitude 528 km) \\  & & IR: 5.5 m (altitude 528 km) \\ \hline \multirow{3}{*}{Spectral bands} & Pan: 450–900 nm & Pan: 450–900 nm \\  & Blue: 450–520 nm & Blue: 450–520 nm \\ \cline{1-1}  & Green: 520–600 nm & Green: 520–600 nm \\ \cline{1-1}  & Red: 630–690 nm & Red: 630–690 nm \\ \cline{1-1}  & NIR: 760–900 nm & NIR: 760–900 nm \\ \cline{1-1}  & & MWIR: 3300–5200 nm \\ \hline Radiometric resolution & 14 bit & 14 bit \\ \hline Modulation Transfer Function & PAN \(\geq\)8\% & PAN \(\geq\)10\% \\ (MTF) & MS \(\geq\)12\% & MS \(\geq\)13\% \\ \hline Signal-to-Noise Ratio (SNR) & \(>\)100 for Pan and MS & \(>\)100 for Pan and MS \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detailed specifications of KOMPSAT-3 and -3A sensors. and the right column is a subset of images of the multispectral bands from KOMPSAT-3 and -3A. For the field campaigns, we prepared four distinctive radiometric tarps with reflectances ranging from approximately 3% to 60% (Figure 1b,d,f). The canvas tarps were chemically treated to obtain constant reflectance values from the samples. The size of each of tarp was 10 m \(\times\) 20 m; at the Mongolia site, larger tarps were used (20 m \(\times\) 20 m, Figure 1f). Considering the spatial resolution of KOMPSAT-3 and -3A, the minimum number of observed pixels in the horizontal direction for tarps in the satellite image was 3 for KOMPSAT-3 and 4 for -3A. We selected the center pixels of each tarp as reference pixels to minimize radiometric interference from neighboring pixels since the size of the tarps are wider than the effective function of the point spread function of the AEISS charge-coupled device (CCD) camera [31; 32]. Figure 1: _Cont._  
For the vicarious calibration, we performed several field campaigns at each site to acquire reliable tarp reflectance values; however, the available images for sensor calibration were limited due to cloudy weather conditions.