Group delay variations of GPS transmitting and receiving antennas

Abstract

GPS code pseudorange measurements exhibit group delay variations at the transmitting and the receiving antenna. We calibrated C1 and P2 delay variations with respect to dual-frequency carrier phase observations and obtained nadir-dependent corrections for 32 satellites of the GPS constellation in early 2015 as well as elevationdependent corrections for 13 receiving antenna models. The combined delay variations reach up to 1.0 m (3.3 ns) in the ionosphere-free linear combination for specific pairs of satellite and receiving antennas. Applying these corrections to the code measurements improves code/carrier single-frequency precise point positioning, ambiguity fixing based on the Melbourne-Wübbena linear combination, and determination of ionospheric total electron content. It also affects fractional cycle biases and differential code biases.

Nadir-Dependent GNSS Code Biases and Their Effect on 2D and 3D Ionosphere Modeling

“…To separate the nadir-dependent part of the GDV from noise and local multipath, a spherical harmonics expansion of degree 5 and order 0 was used as regression model. This regression model for determination of nadir-dependent GDV was demonstrated by the authors of [12]. With this technique, high-frequency variations, probably consisting of noise and local high-frequency multipath, are filtered away, while low-frequency variations persist.…”

“…Later studies also proved the existence of prominent nadir-dependent GDV of BeiDou second generation medium Earth orbiting (MEO) and inclined geosynchronous orbiting (IGSO) satellites [11]. Less prominent nadir-dependent GDV have also been demonstrated to exist for GPS observations [12].…”

“…Thereby, an offset exists in addition to the expected offset due to different ionospheric influence caused by the difference in carrier frequencies. However, even though these biases have been assumed to be constant, recent findings by Hauschild et al [10], Wanninger and Beer [11], and Wanninger et al [12] show that the code biases also have a nadir-dependent component, with the largest effects shown for BeiDou [11], but with measurable effects also shown for other GNSSs [12]. These varying biases of the code observables are also referred to as group delay variations (GDV).Previous studies by Wanninger and Beer [11] and Wanninger, Sumaya, and Beer [12] have shown that nadir-dependent GDV affect precise point positioning (PPP) based on the single frequency ionosphere-free combination, wide-lane ambiguity fixing based on the Hatch-Melbourne-Wübbena linear combination [13][14][15], as well as TEC estimation of the ionosphere.…”

“…Additionally, this approach demonstrates an alternative way of proving the existence of such biases. Earlier studies have employed the multipath (MP) linear combination [10][11][12], while, in this study, we derived the corresponding relationships from ionosphere modeling, and more specifically, the geometry-free linear combination of GNSS observations. This study thereby presents a method independent of the previously employed methods for the determination of the nadir dependence of GDV.The ionosphere modeling was performed regionally over an area covering Sweden with GNSS observations from SWEPOS, the national network of continuously operating reference stations (CORS) in Sweden [28] (Supplementary Materials).…”

Development of the dual‐frequency dual‐constellation airborne multipath models

“…In recent years, it has been shown that these errors vary depending of nadir angle. 17 However, these errors are much smaller compared with the multipath error and the errors introduced by the receiver antenna. Thus, in this work, the contribution of the errors introduced by the satellite antenna is not considered further, and it is assumed that they are not dominant in the multipath estimation process.…”