Codephase center corrections for multi GNSS signals and the impact of misoriented antennas

Abstract

In absolute positioning approaches, e.g. Precise Point Positioning (PPP), antenna phase center corrections (PCC) have to be taking into account. Beside PCC for carrier phase measurements, also codephase center corrections (CPC) exist, which are antenna dependent delays of the code. The CPC can be split into a codephase center offset (PCO) and codephase center variations (CPV). These corrections can be applied in a Single Point Positioning (SPP) approach, to improve the accuracy in the positioning domain. The CPC vary with azimuth and elevation and are related to an antenna, which is oriented towards north. If the antenna is wrongly oriented, the effect cannot be compensated and wrong corrections will be added to the observations.

The Institut für Erdmessung (IfE) established a concept to determine CPC for multi GNSS signals, where a robot tilts and rotates an antenna under test precisely around a specific point. Afterwards time differenced single differences are calculated, which are the input to estimate the CPC by using spherical harmonics (8,8). First studies in our working group showed, that an improvement of the position in a SPP are possible, if antenna pattern for the codephase are considering and correctly applied.

In this contribution, we present the improvement of a SPP and PPP approach by considering CPC for different low cost antennas with multi GNSS signals. Beside the positioning domain, an analysis of the CPC in observation domain, by evaluating the deviations of single differences from zero mean, is performed. Furthermore, we quantify the impact of a disoriented antenna, e.g. oriented in east direction, in the positioning and observation domain by using north oriented CPC. We show, that this impact can be compensating in a post-processing by rotating the antenna pattern. Finally, we present some results of different calibrations, where the antennas are disoriented on the robot and compared to the estimated CPC pattern with the post-processing approach and discussed their impact on the positioning.