Effective Spatial Resolution from Airborne and UAV Sensors Using Siemens Star

This study uses Siemens star test patterns to investigate the effective spatial resolution of airborne and UAV sensors. The Siemens star, a standard calibration tool for optical systems, evaluates resolving power and detects optical aberrations by assessing fine detail resolution as a function of spatial frequency. Calibration was conducted at a unified calibration site, where different sensors, including the Ultracam Eagle, UAV RGB (Sony RX1 RII), and UAV multispectral (ALTUM-PT) systems, were tested. Siemens stars with sector angles of 10° was employed to measure resolution under varying conditions. Quantitative analysis revealed that the Ultracam Eagle achieved a spatial resolution of 10.6 cm and a Ground Sampling Distance (GSD) of 10.3 cm, while UAV multispectral and RGB sensors achieved resolutions of 7 cm and 3.1 cm, respectively, significantly higher than their GSD ($5.17 \mathrm{~cm}, 1.76 \mathrm{~cm}$). The qualitative assessment confirmed that Siemens star patterns showed no significant optical distortions. The results emphasize that field calibration is essential in the case of non-metric cameras for accurate performance evaluation, as laboratory settings may not fully capture operational performance.