Precise GPS Positioning Improvements by Reducing Antenna and Site Dependent Effects

In order to estimate the characteristics of GPS antennas this paper describes a new approach for the estimation of absolute phase center variations (PCV) in a field calibration. The main objective of this approach is the elimination of multipath from the GPS observable and the elimination of any influence of the reference antenna. This is achieved by forming the so called mean sidereal day time difference between observations of successive days. Since the satellite geometry of GPS satellites repeats every mean sidereal day multipath does as well. Therefore, by differentiating observations of two different days multipath can be eliminated. To gain information about the PCV special rotations have to be applied to the antenna of interest. The paper shows the results for three different antenna types.A second application of the mean sidereal day time difference shows the estimation of small position changes between consecutive days. The mean sidereal day time difference is formed in the same manner as for antenna calibration, however, without any rotation. Therefore multipath and PCV are eliminated from the observable. We achieved with observation periods of 10 minutes a horizontal position resolution of only 1.2 mm which is better than results from standard data processing.