Advances in Earth observation technologies have enabled mid-sized satellites to achieve high radiometric performance at relatively low cost, expanding their use to quantitative remote sensing applications. Compact Advanced Satellite 500-4 (CAS500-4), equipped with visible-to-near-infrared sensors including a red-edge band and designed to provide nearly 5-meter multispectral imagery every 3 days, requires a reliable radiometric monitoring framework. Cross-sensor comparison offers an efficient means of validating radiometric stability, particularly through reference sensors such as LANDSAT-8 Operational Land Imager (OLI), whose long-term calibration record ensures high radiometric consistency. This study evaluates whether forest-dominant regions on the Korean Peninsula, which represent the primary observation target of CAS500-4, can serve as suitable ground targets for cross-validation between LANDSAT-8 radiance and KOMPSAT-3 multispectral digital number (DN) values. Five KOMPSAT-3 scenes acquired near-nadir on 13 January 2025 were paired with the same-day Landsat-8 imagery. To mitigate geometric and spatial-resolution mismatches, zonal statistics and a pixel-based sliding-window sampling method (1,681 windows) were applied. Results showed that zonal-mean DN values from KOMPSAT-3 were highly stable across sliding windows, with standard deviations generally below 2 DN. Derived radiance conversion coefficients in the visible bands differed by less than 6% from previous KOMPSAT-3 radiometric studies, demonstrating the strong feasibility of the proposed method. Larger discrepancies in the near-infrared band were attributed to water-dominant landcover and nonlinear sensor response at low DN levels. Overall, forest regions exhibited stable reflectance characteristics suitable for radiometric comparison, suggesting that Korean forests provide a practical and effective foundation for CAS500-4 radiometric validation after launch.



Keywords : Cross validation, CAS500-4, LANDSAT-8, KOMPSAT-3, Forest, Remote sensing