Study on Establishment Method of High Precision True-North Azimuth Reference

In order to calibrate the instrument constant and precision of gyro theodolite and gyro north-seeker, it is necessary to establish the true north azimuth reference. In this paper, the methods and implementation techniques of establishing high precision true-north azimuth reference are discussed. In order to solve the calibration problem of gyro theodolite and north-seeker with different aiming ways, the combined north orientation positioning method is adopted. Using two collimators and a plane mirror as the true-north azimuth reference, the collimating normal northward reference and the infinite northward reference were established, and a set of calibration devices for gyro theodolite calibration with different aiming modes was realized. The method of astronomical orientation is used to assign values to the north azimuth reference. A method of synchronous opposite observation with two Leica5100A 0.5" electronic theodolites is proposed. The azimuth angles of Polaris measured outdoors are directly transferred to the indoor reference plane mirror and collimator to assign values to the north azimuth reference. The first north azimuth valuation test was conducted on October 19 and 20, 2017. Through a total of 6 back observations in 2 periods, the mean error of the three true north azimuth reference calculated is as high as 0.17 ", 0.18 "and 0.20" respectively. The retest was conducted on October 11 and 12, 2018. The mean error of the three true north azimuth reference was 0.47 ", 0.30 "and 0.48", respectively, and the retest results about one year later showed that the three references changes were + 3.84 ", + 1.96 "and + 3.80" respectively, which shows that the benchmark are very stable and the technical measures and methods are very effective. This method can be used as a reference for the establishment of gyro theodolite and gyro north-seeker calibration devices.