Auto-Cal: Automated and Continuous Geo-Referencing of All-Sky Imagers Using Fisheye Lens Modeling and Star Tracks

Abstract: A fully automated and continuous calibration framework for All-Sky Imagers (ASIs) that significantly enhances the spatial accuracy and reliability of geo-referenced ASI data is presented. The technique addresses a critical bottleneck in ASI image data reliability and usability for real time space weather via automated geo-referencing under real-world field conditions. The system corrects the lens distortion in ASIs using a well-established fisheye lens model and automatically estimates camera orientation in terms of roll, pitch, and yaw angles relative to True North and the horizontal plane perpendicular to the zenith using star tracking. Unlike traditional methods that require manual intervention and periodic recalibration, Auto-Cal performs nightly unattended recalibrations using observed stellar motion, adapting to mechanical shifts or environmental changes. Each calibration step includes formal error estimates, allowing end users to assess the confidence of geo-located data in real-time. This capability enables dependable ASI operations in remote or unmanned settings and supports higher-fidelity integration with other geophysical instruments. Auto-Cal provides a scalable foundation for maintaining a large array of ASIs, thus enabling long-term atmospheric monitoring and real-time space weather alerts.