Evaluation of a GPS-Based Approach for Rapid and Precise Determination of Geodetic/Astronomical Azimuth

The rapid and precise determination of the azimuth information, purely based on the satellite positioning technology of global positioning system (GPS), is tested and evaluated by this paper. The main consideration of using GPS for the azimuth determination is expected to replace the traditional astronomical azimuth measurement, which is believed to be time-consuming and weather-dependent. A GPS approach is simply based on setting up the GPS receivers at the two ends of a baseline, recording and processing the phase observable, and converting its coordinate solution into an azimuth with the inverse geodetic formulas. This type of azimuth obtained by the GPS static solution has been assessed to be well consistent with the astronomical azimuth by a level of better than $\pm 1^{″}$ . The GPS kinematic mode of azimuth value, however, is biased from the standard value for a RMS error of $\pm 9^{″}$ . The correction of the deflection of the vertical, theoretically required by the geodetic and astronomical azimuth conversion, is also implemented and found to be only effective at the observation site where the $\eta \tan \phi$ value is higher than the estimation accuracy of the $\eta$ value provided by a gravimetric geoid model.