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Ch Reigber - One of the best experts on this subject based on the ideXlab platform.

  • impact of gps Satellite Antenna offsets on scale changes in global network solutions
    Geophysical Research Letters, 2005
    Co-Authors: M Ge, G Gendt, Galina Dick, F P Zhang, Ch Reigber
    Abstract:

    [1] In this paper, we demonstrate that biases in the GPS Satellite Antenna phase center offsets could lead to scale biases in global network solutions, which change along with the observed Satellite constellation. To validate the IGS standard offset values, Satellite-specific offsets are estimated from GPS data and the network solutions are re-adjusted with these estimates. Both the estimated offsets and the re-adjusted network scales confirmed that the IGS standard offsets are significantly biased and produce scale changes of more than 1 ppb. From investigations of the offset inhomogeneities among Satellites belonging to the same block type, it is strongly recommended that block-type-specific offsets used presently as IGS standard should be replaced by Satellite-specific ones.

  • Satellite Antenna phase center offsets and scale errors in gps solutions
    Journal of Geodesy, 2003
    Co-Authors: F H Massmann, Yue Qui Yu, Ch Reigber
    Abstract:

    ITRF2000 solutions have shown that there are parts-per-billion (ppb)-level scale differences between GPS and other techniques, as well as among various GPS analysis centers (ACs). The trends of the scale differences reach 0.2 ppb per year. It is demonstrated that the uncertainty in the Satellite Antenna phase center offset (z-direction) is one of the major reasons for the scale differences. The scale change caused by an error in the z_offset can be approximately expressed as: scale change (in ppb)=7.8 × error of z_offset (in meters). Changing the z_offset value of the BLOCK II and IIA Satellites from 102 to 95 cm could produce a 0.5-ppb scale variation. For BLOCK IIR Satellites the uncertainty of the z_offset is much larger. The number of these Satellites increases each year. The accuracy of IGS products could be significantly affected if this problem is not properly solved. Besides scale, Satellite Antenna phase center uncertainties have perceptible effects on also the clock, zenith path delay, and other solved-for parameters.

Markus Rothacher - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of elevation-dependent Satellite Antenna phase center variations of GPS Satellites
    Journal of Geodesy, 2003
    Co-Authors: R. Schmid, Markus Rothacher
    Abstract:

    A method for the estimation of the phase center variations of GPS Satellite Antennas using global GPS data is presented. First estimations have shown an encouraging repeatability from day to day and between Satellites of the same block. Thus, two different Satellite Antenna patterns for Block II/IIA and for Block IIR with a range of about 4 cm and an accuracy of less than 1 mm could be found. The present approach allows the creation of a consistent set of receiver and Satellite Antenna patterns and phase center offsets. Thereby, it is possible to switch from relative to absolute phase center variations without a scale problem in global networks. This changeover has an influence on troposphere parameters, reduces systematic effects due to uncorrect Antenna modeling and should diminish the elevation dependence of GPS results.

R. Schmid - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of Satellite Antenna phase center offsets for Galileo
    Journal of Geodesy, 2016
    Co-Authors: Peter Steigenberger, R. Schmid, Rolf Dach, Mathias Fritsche, Oliver Montenbruck, Maik Uhlemann, Lars Prange
    Abstract:

    Satellite Antenna phase center offsets for the Galileo In-Orbit Validation (IOV) and Full Operational Capability (FOC) Satellites are estimated by two different analysis centers based on tracking data of a global GNSS network. The mean x- and y-offsets could be determined with a precision of a few centimeters. However, daily estimates of the x-offsets of the IOV Satellites show pronounced systematic effects with a peak-to-peak amplitude of up to 70 cm that depend on the orbit model and the elevation of the Sun above the orbital plane. For the IOV y-offsets, no dependence on the orbit model exists but the scatter strongly depends on the elevation of the Sun above the orbital plane. In general, these systematic effects are significantly smaller for the FOC Satellites. The z-offsets of the two analysis centers agree within the 10–15 cm level, and the time series do not show systematic effects. The application of an averaged Galileo Satellite Antenna model obtained from the two solutions results in a reduction of orbit day boundary discontinuities by up to one third—even if an independent software package is used.

  • Estimation of elevation-dependent Satellite Antenna phase center variations of GPS Satellites
    Journal of Geodesy, 2003
    Co-Authors: R. Schmid, Markus Rothacher
    Abstract:

    A method for the estimation of the phase center variations of GPS Satellite Antennas using global GPS data is presented. First estimations have shown an encouraging repeatability from day to day and between Satellites of the same block. Thus, two different Satellite Antenna patterns for Block II/IIA and for Block IIR with a range of about 4 cm and an accuracy of less than 1 mm could be found. The present approach allows the creation of a consistent set of receiver and Satellite Antenna patterns and phase center offsets. Thereby, it is possible to switch from relative to absolute phase center variations without a scale problem in global networks. This changeover has an influence on troposphere parameters, reduces systematic effects due to uncorrect Antenna modeling and should diminish the elevation dependence of GPS results.

Gunnar Elgered - One of the best experts on this subject based on the ideXlab platform.

  • Ground-Based GPS for Validation of Climate Models: The Impact of Satellite Antenna Phase Center Variations
    IEEE Transactions on Geoscience and Remote Sensing, 2010
    Co-Authors: Per Jarlemark, Ragne Emardson, Jan Johansson, Gunnar Elgered
    Abstract:

    The amount of water vapor in the atmosphere is an important indicator for climate change. Using the Global Positioning System (GPS), it is possible to estimate the integrated water vapor (IWV) above the ground-based GPS receiver. In order to optimally determine the IWV, a correct model of the received signal phase is essential. We have studied the effect of the Satellite Antenna phase center variations (PCVs) on the IWV estimates by simulating the effect and by studying the estimates of the IWV based on the observed GPS signals. During a period of five years, from 2003 to 2008, a new Satellite type was introduced, and it steadily grew in numbers. The Antenna PCVs for these Satellites deviate from the earlier Satellite types and contribute to excess IWV estimates. We find that ignoring Satellite Antenna phase variations for this time period can lead to an additional IWV trend of about 0.15 kg/m2/year for regular GPS processing.

F H Massmann - One of the best experts on this subject based on the ideXlab platform.

  • Satellite Antenna phase center offsets and scale errors in gps solutions
    Journal of Geodesy, 2003
    Co-Authors: F H Massmann, Yue Qui Yu, Ch Reigber
    Abstract:

    ITRF2000 solutions have shown that there are parts-per-billion (ppb)-level scale differences between GPS and other techniques, as well as among various GPS analysis centers (ACs). The trends of the scale differences reach 0.2 ppb per year. It is demonstrated that the uncertainty in the Satellite Antenna phase center offset (z-direction) is one of the major reasons for the scale differences. The scale change caused by an error in the z_offset can be approximately expressed as: scale change (in ppb)=7.8 × error of z_offset (in meters). Changing the z_offset value of the BLOCK II and IIA Satellites from 102 to 95 cm could produce a 0.5-ppb scale variation. For BLOCK IIR Satellites the uncertainty of the z_offset is much larger. The number of these Satellites increases each year. The accuracy of IGS products could be significantly affected if this problem is not properly solved. Besides scale, Satellite Antenna phase center uncertainties have perceptible effects on also the clock, zenith path delay, and other solved-for parameters.