Photometry-free sky area visibility estimation method for Allsky Camera postprint

Abstract: Observatories typically deploy all-sky cameras for monitoring cloud cover and weather conditions. However, many of these cameras lack scientific-grade sensors, resulting in limited photometric precision, which makes calculating the sky area visibility distribution via extinction measurement challenging. To address this issue, we propose the Photometry-Free Sky Area Visibility Estimation (PFSAVE) method. This method uses the standard magnitude of the faintest star observed within a given sky area to estimate visibility. By employing a pertransformation re-fitting optimization strategy, we achieve a high-precision coordinate transformation model with an accuracy of 0.42 pixels. Using the results of Source Extractor, we propose screening criteria to reduce false detections. HEALPix segmentation is also introduced to achieve high spatial resolution. Comprehensive analysis based on real allsky images demonstrates that our method exhibits higher accuracy than the extinction-based method. Our method supports both manual and robotic dynamic scheduling, especially under partially cloudy conditions.