Calibration method for the optical system of infrared CMOS-theodolite in astronomical measurement

The all-day astronomical measurement system, which integrates a theodolite with an infrared sensor, offers substantial advantages in miniaturization, automation, speed, measurement accuracy, and efficiency, enabling comprehensive all-day astronomical observations. High-precision instrument calibration is a core prerequisite for obtaining accurate astronomical measurement results, which directly determines the reliability and effectiveness of the system's observation data. However, the system features a removed eyepiece and a small optical field of view; in addition, its complementary metal-oxide-semiconductor (CMOS) sensor is equipped with low pixel resolution, making existing conventional calibration methods incompatible and unable to meet high-precision calibration requirements. This study utilizes a self-developed astronomical measurement system as a platform, fully integrating the theodolite's angle measurement data to propose a novel calibration method. The approach initially determines the target point's direction value and partial camera parameters through two-face measurement, which then serves as known information for computing principal point pixel coordinates using face I/II data. To verify the effectiveness and reliability of the proposed method, calibration experiments are first conducted to obtain a set of well-calibrated parameters with high precision. On this basis, astronomical positioning experiments are carried out in two typical observation environments: daytime and nighttime. Preliminary experimental results show that the proposed calibration method can stably and reliably acquire high-precision calibration parameters of the optical system, providing solid technical support for subsequent astronomical observations. Compared to established astronomical reference points, the root mean square errors (RMSEs) for daytime astronomical longitude and latitude measurements were within 0.33″ and 0.34″, respectively, whereas night-time measurements achieved RMSEs of 0.26″ and 0.29″, respectively. These findings highlight the method's potential for improving the accuracy, robustness, and practical applicability of astronomical measurements across diverse observational environments, contributing to advancements in modern astronomical observation technologies.