Early-Stage Non-Stellar Pointing Characterization of a Cherenkov Telescope Prototype Using Distributed Multi-Sensor Measurements

Abstract To investigate the fine morphology and radiation mechanisms of ultra-high-energy gamma-ray sources, the Large Array of Imaging Atmospheric Cherenkov Telescopes (LACT), comprising 32 imaging atmospheric Cherenkov telescopes, is under construction at the Large High Altitude Air Shower Observatory (LHAASO). This imposes stringent requirements on the angular resolution and pointing accuracy of the telescope system. The mount-level pointing-error contribution and tracking stability are critical to data quality, with a mechanical error allocation below 0.01°. However, conventional star-based calibration relies on fully integrated optical systems, causing a substantial verification lag during early construction. Furthermore, its parametric-fitting nature hinders independent error decoupling, providing limited physical guidance for structural optimization. In this study, a distributed multi-sensor method is proposed and validated using the first LACT engineering prototype to characterize the mount's mechanical performance. The approach integrates a network of dual-axis inclinometers, a vision measurement system, and high-precision encoders to quantify mount-level pointing performance and major mechanical error sources across different orientations. An error compensation model incorporating a measured look-up table (LUT) was subsequently developed. Experimental results show that the LACT prototype mount satisfies the allocated mount-level mechanical performance requirements under the tested conditions. The hierarchical inclinometer network reveals azimuth-dependent attitude variations of the mount, enabling the generation of a measurement-derived LUT for mount-level correction. Continuous target-return tests based on the vision measurement system show repeat positioning deviations below 0.005° over a two-week period under the tested conditions, supporting the long-term repeatability of the mount. Overall, this method enables quantitative mount-level characterization and pre-calibration of large ground-based telescope mounts without relying on stellar observations or fully operational optical pointing calibration.