Tomographic determination of the spatial distribution of water vapor using GPS observations

Abstract With the advent of the GPS navigation system, a promising ground based technique has been introduced which makes it possible to estimate the amount of water vapor in the troposphere from operational GPS networks at relatively low additional costs. While the estimation of the integrated amount is currently well established, the determination of the spatial water vapor distribution and its temporal variation are still a major challenge. To account for the vertical resolution, several tomographic approaches were pursued. We developed the software package AWATOS (atmospheric water vapor tomography software) which is based on the assimilation of double differenced GPS observations. Applying a least-squares inversion, the inhomogeneous spatial distribution of water vapor is determined. An extensive investigation has been carried out in Switzerland. GPS measurements are performed by the dense permanent Swiss national GPS network AGNES of the Swiss Federal Office of Topography (swisstopo). A total of 40 equally distributed water vapor profiles have been estimated on an hourly basis. For the purpose of validation, 22 radiosonde profiles were used at the GPS and meteorological station Payerne. Furthermore, data of the numerical weather model aLMo (alpine model in Switzerland, MeteoSwiss) were compared with the tomographic results. An overall good agreement of the three methods with an rms of better than 1.6 g/m3 absolute humidity was achieved. The results show that AGNES can be used as a dedicated network for the purpose of GPS-tomography, using a horizontal resolution of approximately 50 km and height layers of 300–500 m thickness in the lower troposphere.

[1]  M. Troller,et al.  GPS based determination of the integrated and spatially distributed water vapor in the troposphere , 2004 .

[2]  Edward M. Mikhail,et al.  Observations And Least Squares , 1983 .

[3]  L. Mervart,et al.  Bernese GPS Software Version 5.0 , 2007 .

[4]  Soren W. Henriksen,et al.  The Use of artificial satellites for geodesy , 1972 .

[5]  T. Herring,et al.  GPS Meteorology: Remote Sensing of Atmospheric Water Vapor Using the Global Positioning System , 1992 .

[6]  S. Park.  Nonlinearity and predictability of convective rainfall associated with water vapor perturbations in a numerically simulated storm , 1999 .

[7]  G. Ruffini,et al.  4D tropospheric tomography using GPS slant wet delays , 2000 .

[8]  D. J. Allerton,et al.  Book Review: GPS theory and practice. Second Edition, HOFFMANNWELLENHOFF B., LICHTENEGGER H. and COLLINS J., 1993, 326 pp., Springer, £31.00 pb, ISBN 3-211-82477-4 , 1995 .

[9]  V. Mendes,et al.  Modeling the neutral-atmosphere propagation delay in radiometric space techniques , 1998 .

[10]  Alain Geiger,et al.  3‐D refractivity field from GPS double difference tomography , 2002 .

[11]  Lars Peter Kruse.  Spatial and temporal distribution of atmospheric water vapor using space geodetic techniques , 2000 .

[12]  Kazuro Hirahara,et al.  Local GPS tropospheric tomography , 2000 .

[13]  V. Ducrocq,et al.  Storm-Scale Numerical Rainfall Prediction for Five Precipitating Events over France: On the Importance of the Initial Humidity Field , 2002 .