Measuring and modelling variations in the distribution of atmospheric water vapour using GPS
Doktorsavhandling, 2008

Turbulence introduce variations in the refractive index of air, which in turn result in fluctuations in the phase and amplitude of radio signals propagating through the atmosphere. Most important are the variations due to fluctuations in the water vapour field. These fluctuations limit the accuracy of space geodetic techniques such as VLBI (Very Long Baseline Interferometry) and GNSS (Global Navigation Satellite Systems). In order to obtain the highest possible accuracy it is important to understand these effects. In this thesis several different techniques for measurements of turbulence induced refractive index variations are presented. Using data from high resolution radiosondes vertical profiles of the variations above the radiosonde station can be obtained. Vertical average of the magnitude of the variations can be studied by using a radiometer to investigate the variations in the slant wet delays as function of direction. Similarly, GNSS data from several GNSS stations in a network could be used to investigate the variations in the zenith delay as function of location. One area where it is important to have a good modelling of the refractive index variations is in GNSS tropospheric tomography. This technique uses GNSS data from several stations in a dense local network in order to obtain the 3D structure of the atmospheric water vapour. The problem with this technique is that the geometry of the tomographic problem is poor, especially for flat networks, making it very difficult to obtain the vertical water vapour profile. This makes it necessary to use additional information or constraints. One way to obtain such constraints is using information of the refractive index variation from turbulence theory. It is shown in this thesis that if information on the vertical profile of the refractive index variations is available, better estimations of the water vapour profile could be achieved. If this is not the case the water vapour profile cannot be retrieved very accurately. However, it is shown that when retrieving the horizontal variations in the water vapour field, a higher accuracy is achievable.

Global Positioning System (GPS)

Microwave Radiometry

Water Vapour


Atmospheric Turbulence

EA-salen, EDIT huset, Hörsalsvägen 11
Opponent: Dr. Pedro Elósegui, Institute of Space Studies of Catalonia, Spanien.


Tobias Nilsson

Chalmers, Institutionen för radio- och rymdvetenskap, Rymdgeodesi och geodynamik

Characterizing Atmospheric Turbulence and Instrumental Noise Using Two Simultaneously Operating Microwave Radiometers

Proc. 9:th Specialist Meeting on Microwave Radiometry and Remote Sensing Applications, MicroRad 2006,; (2006)p. 270- 275

Konferensbidrag (offentliggjort, men ej förlagsutgivet)

Simulations of atmospheric path delays using turbulence models

Proceedings of the 18th European VLBI for Geodesy and Astrometry Working Meeting, edited by J. Böhm, A. Pany, and H. Schuh, Geowissenschaftliche Mitteilungen, Schriftenreihe der Studienrichtung Vermessung und Geoinformation, Technische Universität Wien,; (2007)p. 175-180

Konferensbidrag (offentliggjort, men ej förlagsutgivet)

Water Vapor Tomography Using GPS Phase Observations: Simulation Results

IEEE Trans. on Geosci. and Rem. Sens.,; Vol. 44(2006)p. 2927-2941

Artikel i vetenskaplig tidskrift

Water vapour tomography using GPS phase observations: Results from the ESCOMPTE experiment

Tellus,; Vol. 59A(2007)p. 674-682

Artikel i vetenskaplig tidskrift

Temporal correlations of atmospheric mapping function errors in GPS data analysis

Journal of Geodesy,; Vol. 81(2007)p. 311-323

Artikel i vetenskaplig tidskrift

Correlations Between Slant Wet Delays Measured by Microwave Radiometry

IEEE Trans. Geosci. Rem. Sens., GE-43(5),; (2005)p. 1028-1035

Artikel i vetenskaplig tidskrift



Meteorologi och atmosfärforskning


Elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 2745

EA-salen, EDIT huset, Hörsalsvägen 11

Opponent: Dr. Pedro Elósegui, Institute of Space Studies of Catalonia, Spanien.