Development of a tomographic water vapour sounding system based on GNSS data
Zusammenfassung der Projektergebnisse
The Global Positioning System (GPS) has nowadays many applications used in daily life. An increasing number of GPS applications requires dense networks of GPS ground receivers all over the world and induced the development of the European Galileo programme, the Chinese Compass programme as well as the renewal of the Russian GLONASS. Precise positioning applications require atmosphere corrections in order to remove the impact of the lower atmosphere and especially the water vapour on the GPS signal and the position. These corrections contain valuable information on the atmospheric state and are the basic input for several applications of the GPS meteorology or GPS atmosphere sounding. The GPS vater vapour tomography makes use of the atmosphere corrections applied to each individual transmitter-receiver link. Each signal path from a GPS satellite to a ground receiver “scans” a different part of the atmosphere and provides information integrated along the signal path. A very large number of such observations can be used to reconstruct the atmospheric state by means of tomographic techniques. This project was started to set up a continuously running GPS based water vapour sounding system for Germany. Currently, about 270 German GPS stations provide ~1.2 millions of observations per day, each covering a different region of the atmosphere. Humidity fields with a spatial resolution of about 40 km horizontally and several hundred meters vertically can be reconstructed from these observations every 15-30 minutes. The tomography system is now in a semi-operational state and can run in near real-time as part of the GPS processing system or be used to reconstruct user defined periods of time with various parameters. GPS slant delays are operationally available since 2007 and this large data set was used to obtain a large number of humidity fields which cover Germany and parts of adjacent countries. The results were validated using independent observations such as radiosonde profiles, the line of sight integrated water vapour of water vapour radiometers and analyses of numerical weather models which provide an optimal combination of all observations. The validation showed that the GPS observations present sufficient information to reconstruct 3D humidity fields of good quality as long as all parts of the atmosphere are “scanned” by GPS signal paths. Currently, this is the case only for limited regions and periods. The number and distribution of GPS observations does not yet cover all parts of Germany at all times. Rather large unobserved regions affect the quality of the results and more stations and satellites would be required by an operational GPS tomography system. The number of satellites is already increasing as GLONASS, Compass and Galileo will soon be available. Beyond that attempts must be made to densify the GNSS networks as the resolution of the reconstructed humidity fields is limited by the interstation distances.
Projektbezogene Publikationen (Auswahl)
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(2008). Validation of GPS Slant Delays using Water Vapour Radiometers and Weather Models, Meteorologische Zeitschrift, 17(6): 807-812
M. Bender, G. Dick, J. Wickert, T. Schmidt, S. Song, G. Gendt, M. Ge and M. Rothacher
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(2009). Estimates of the information provided by GPS slant data observed in Germany regarding tomographic applications, Journal of Geophysical Research, 114: D06303
M. Bender, G. Dick, J. Wickert, M. Ramatschi, M. Ge, G. Gendt, M. Rothacher, A. Raabe and G. Tetzlaff
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(2009). Retrieving Tropospheric Delays from GPS Networks Densified with Single Frequency Receivers, Geophysical Research Letters, Vol. 36, L19802
Z. Deng, M. Bender, G. Dick, M. Ge, J. Wickert, M. Ramatschi, X. Zou
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(2011). Analysis of a dryline-like feature in northern Germany detected by ground-based microwave profiling, Meteorologische Zeitschrift, Vol. 20, 409-421
D. Spänkuch, J. Güldner, H. Steinhagen, M. Bender
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(2011). Development of a GNSS Water Vapor Tomography System Using Algebraic Reconstruction Techniques, Advances in Space Research, Vol. 47, No. 10, 1704-1720
M. Bender, G. Dick, M. Ge, Z. Deng, J. Wickert, H.-G. Kahle, A. Raabe, G. Tetzlaff
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(2011). GNSS water vapour tomography – Expected improvements by combining GPS, GLONASS and Galileo observations, Advances in Space Research, Vol. 47, No. 5, 886-897
M. Bender, R. Stosius, F. Zus, G. Dick, J. Wickert, A. Raabe
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(2011). On the relationship between water vapour field evolution and the life cycle of precipitation systems, Quarterly Journal of the Royal Meteorological Society, Vol. 137, 204-223
J. Van Baelen, M. Reverdy, F. Tridon, L. Labbouz, G. Dick, M. Bender, M. Hagen
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(2011). Validation of tropospheric slant path delays derived from single and dual frequency GPS receivers, Radio Science, Vol. 46, RS6007
Z. Deng, M. Bender, F. Zus, M. Ge, G. Dick, M. Ramatschi, J. Wickert, U. Löhnert, S. Schön
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(2012). A methodology to compute GPS slant total delays in a numerical weather model, Radio Science, Vol. 47, RS2018
F. Zus, M. Bender, Z. Deng, G. Dick, S. Heise, M. Shangguan, J. Wickert
