The Compact Advanced Satellite 500-4 (CAS500-4) is scheduled for launch in 2025 and is expected to play a significant role in monitoring agricultural and forest resources across the Korean Peninsula. However, the absence of actual CAS500-4 data prior to launch presents challenges for pre-launch research and verification, which constrains the ability to reflect the distinctive attributes of the satellite accurately. To address this issue, this study proposes a method for generating CAS500-4 Level-1 Radiometric (L1R) simulated images by inverse orthorectification based on the rational function model (RFM). Sentinel-2 orthoimages were used as the base image, and rational polynomial coefficients (RPCs) collected from Korea Multi-Purpose Satellite-3A (KOMPSAT-3A) were adjusted and utilized. The objective was to meet the ground sample distance (GSD) requirement of 5 m, consistent with CAS500-4 specifications, and to simulate different viewing angles from the base orthoimage using adjusted RPCs. The results demonstrated that the proposed method established a relationship with the base orthoimage and generated L1R simulated images. These simulated images provide a reliable basis for validating operational processes and preparing for various applications, ensuring effective utilization of CAS500-4 during its early operations.





Keywords CAS500-4, Rational function model, Satellite image, Simulated image, Sentinel-2, Inverse orthorectification