Standardized methods for assessing the spatial resolution of airborne photogrammetric systems are essential for ensuring consistent quality in aerial imaging. This study evaluates the use of Siemens stars for empirical estimation of Ground Resolving Distance (GRD) in high-altitude aerial photo missions, based on field experiments conducted in Norway and Denmark during 2023–2025. The results confirm a consistent and expected deviation between Ground Sampling Distance (GSD) and GRD, reinforcing GRD as a critical parameter for planning, procurement, and quality assurance in airborne photo missions. The study also shows that using external reference plates to obtain reliable black and white reference values improves the reliability of GRD estimations while simultaneously enabling using smaller Siemens star. This supports the use of the GRD method as a robust and practical framework for spatial resolution assessment in aerial imagery. The fundamental objective of the project is to establish common recommendations and methodologies for aerial image quality assessment, ultimately contributing to a European-wide GRD based resolution standard. Overall, structured and transparent GRD verification is necessary to ensure consistent quality in airborne optical imagery.