Full Record

New Search | Similar Records

Author
Title GPS tropospheric modelling: new developments and insights
URL
Publication Date
Date Accessioned
University/Publisher Australian National University
Abstract GPS is widely used to monitor temporal and spatial variations of Earth’s crust, oceans and atmosphere. Of particular interest to this research is the use of GPS for studying variations in the Earth’s lower atmosphere. While there have been significant advances in the techniques and models used in GPS analyses over the past two decades, there is still room for improvement. In particular, observations at very low elevation angles still suffer greatly from modelling errors. These low-elevation observations provide useful information about the moisture content of the atmosphere and its variability around a GPS station, and are thus valuable data for meteorological studies if properly modelled. The main focus of this thesis is on optimization of the techniques and models used in GPS analysis for more accurate estimates of the tropospheric delays. Particular attention is paid to modelling low-elevation observations and challenging weather conditions. Throughout the thesis, we investigate several different aspects of modelling techniques and how each of them affect the tropospheric estimates. By applying a previously developed empirical model [Moore, 2015], the site-specific errors are shown to have large impacts on the tropospheric delay estimates: empirical mitigation of site-specific errors leads to improved repeatabilities of heights and tropospheric zenith delays for the majority of the stations in our analysis. The empirical site-specific model also significantly reduces the sensitivity of tropospheric zenith delay estimates to the choice of elevation cut-off. Another important potential source of error, the GPS estimates of tropospheric horizontal gradients are shown to be more accurate than the model values currently available. However, the conventional two-axis planar model of gradients does not accurately represent the actual gradients of the refractivity under weather conditions with asymmetric horizontal changes of refractivity. Such abnormal conditions may occur due to topography-driven gravity waves in the troposphere, and the mismodelled tropospheric horizontal gradients induce errors in the parameter estimates, sometimes leading to skewed position time series and inaccurate tropospheric zenith delays. A new parametrization of tropospheric gradients whereby an arbitrary number of gradients are estimated as discrete directional wedges is shown via both simulations and real case studies to largely improve the accuracy of recovered tropospheric zenith delays in asymmetric gradient scenarios. The new directional model significantly improves the repeatabilities of the station height time series in asymmetric gradient situations while causing slightly degraded repeatabilities for the stations …
Subjects/Keywords Global Positioning System; Tropospheric delay; Site-specific errors; Tropospheric horizontal gradients; Directional gradient model; Temporal constraints
Language en
Country of Publication au
Record ID handle:1885/148041
Repository anu
Date Retrieved
Date Indexed 2019-12-30
Issued Date 2017-01-01 00:00:00

Sample Search Hits | Sample Images | Cited Works

…aspects of modelling techniques and how each of them affect the tropospheric estimates. By applying a previously developed empirical model [Moore, 2015], the sitespecific errors are shown to have large impacts on the tropospheric delay estimates…

tropospheric zenith delay estimates to the choice of elevation cut-off. Another important potential source of error, the GPS estimates of tropospheric horizontal gradients are shown to be more accurate than the model values currently available. However, the…

…2 Background 2.1 GPS observables, modelling and parameters . 2.2 Tropospheric delay modelling in GPS analyses 2.3 Simulations and Experiments . . . . . . . . . . 2.4 Summary . . . . . . . . . . . . . . . . . . . . . . 3 4 1 3 . . . . 5 5 9 13…

…3.2.1.1 Antenna and radome model errors . . . . . . . . . . . . 3.2.1.2 Multipath error . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Empirical mitigation of site-specific errors . . . . . . . . . . . . . 3.2.3 Use of ESM for tropospheric delay

…GUAM; (b) station NAUR; and (c) station SA40. . . . . . . . . . . . . . . 25 xiii LIST OF FIGURES xiv 3.5 The differences between the tropospheric zenith delay estimates from the solutions with elevation cut-off angles 3◦ and 10…

…from the 10◦ cut-off solution minus the estimates from the 3◦ cut-off solution. . . 27 3.6 The differences between the tropospheric zenith delay estimates from the solutions with elevation cut-off angles 3◦ and 10◦ for TOW2. The elevation-dependent…

…28 3.7 The differences between the tropospheric zenith delay estimates from the solutions with elevation cut-off angles 3◦ and 10◦ for CEDU. The elevation-dependent weighting of Equation 3.1 is used for both solutions. The grey shades are the 1…

…temporal variations of the tropospheric zenith wet delay and horizontal gradients. . . . . . . 110 5.10 Reductions in the mean monthly WRMS of height components over 2011-2012 for different stations when using calibrated process noise levels for…

.