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Water Vapor Movie

Determining IPWV from GPS Data

As part of the standard GPS data analysis performed by the space geodesy group at the Onsala Space Observatory, the time-varying zenith atmospheric propagation delay is estimated for each site. The "hydrostatic delay" component of the propagation delay can be removed from the total delay, yielding only the delay due to water vapor, the "wet delay" [Davis et al., 1985]. The zenith wet delay is proportional to the integrated precipitable water vapor (IPWV) above each site, with the factor of proportionality being fairly constant. The IPWV is the height of a column of water that would result if the water vapor in a vertical column were precipitated out into liquid.

The movie (sample frame shown above) displays the evolution of IPWV for the Swedish Permanent GPS Network (SWEPOS), part of the BIFROST Project [BIFROST Project, 1996]. The data were obtained in December 1993 suring a period of rapidly changing weather in Sweden. Time series of IPWV for the different sites were presented in Davis et al. [1996]. The movie shows 2 days of this period, and the passage of the warm and cold fronts are clearly visible. The movie was created by interpolating and smoothing the IPWV measured at the different sites. The Macintosh program Igor Pro 3 was used for the analysis of the time series, for the creation of the images, and for the creation of the QuickTime movie.

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Retrieve (6.1M) the QuickTime movie of IPWV over Sweden.


BIFROST Project, GPS Measurements to constrain geodynamic processes in Fennoscandia, Eos Trans. AGU, 77, pp. 337 & 341, 1996.

Davis, J. L., T. A. Herring, I. I. Shapiro, A. E. E. Rogers, and G. Elgered, Geodesy by radio interferometry: Effects of atmospheric errors on estimates of baseline length, Radio Science, 20, 1593-1607, 1985.

Davis, J. L., M. L. Cosmo, and G. Elgered, Using the Global Positioning System to study the atmosphere of the Earth: Overview and Prospects, in GPS Trends in Precise Terrestrial, Airborne, and Spaceborne Applications, edited by G. Beutler, G. W. Hein, W. G. Melbourne, and G. Seeber, 338 pp., Springer, New York, 99. 233-242, 1996.

For further information contact:

James Davis
Harvard-Smithsonian Center for Astrophysics
60 Garden St, MS 42
Cambridge, MA 02138-1516
(617) 496-7811