GPS World, July 2010

Remote Sensing INNOVATION ment network to perform a hydrological hazard assessment The comparison of independent techniques showed that the ZTD time series agree within 2 centimeters on average that is to better than 1 percent The correlation of the GPS data and the data derived from the numerical weather model is greater than 70 percent However local rain showers are sometimes more clearly represented by the data of the dense GPS network than by COSMO 7 It is possible to increase the spatial and temporal resolution in GPS tomography so it can enhance numerical weather models The better agreement of the tomographic profiles with radiosonde data compared to the COSMO 7 estimates indicates that the numerical weather prediction models will benefit from additional information on the vertical distribution of water vapor provided by high resolution GPS tomography To assess the potential of near real time GPS tomography IGS satellite products with short latency and fast update rates were tested in the GPS processing With ultra rapid orbits we obtained satisfactory results for the tropospheric parameters in almost real time mode The use of predicted orbits in the tomographic processing degrades the results of the wet refractivity profiles by 20 percent compared to using final that is best available products Conclusions In this brief article we have shown that high resolution GPS tomography is well suited for application in mountainous regions especially in view of its potential to contribute to hydrological hazard assessment We have been able to estimate the wet refractivity field with a spatial and temporal resolution comparable with the current and the next generation of numerical weather models COSMO 2 with 2 kilometer horizontal resolution We have been successful in illustrating several beneficial aspects of GPS tomography in supporting high resolution numerical weather prediction models We would also point out that tomographically determined wet refractivity fields may also be used in conjunction with directly estimated integrated slant path delays to adjust the GPS observations especially those obtained at low elevation angles Implemented in GPS processing software GPS tomography could provide completely anisotropic tropospheric corrections for very high accuracy positioning applications Acknowledgments The research discussed in this article was financially supported by the Swiss National Science Foundation and the Swiss Geodetic Commission The Swiss Federal Office of Meteorology and Climatology MeteoSwiss and the Swiss Federal Office of Topography Swisstopo provided necessary data sets for processing analyzing and validating the results Furthermore O Heller and Dr A Somieski supported the field work and several residents or public organizations in the canton of Valais offered their premises for temporary mounting of the campaign measurement systems SIMON LUTZ is a research fellow at the Astronomical Institute of the University of Bern Switzerland and a member of the Center for Orbit Determination in Europe analysis center team He received M S and Ph D degrees in geodesy and geodynamics from the Swiss Federal Institute of Technology ETH Zurich Switzerland MARC TROLLER is a communications navigation and surveillance CNS expert at Swiss Air Navigation Services Ltd Skyguide Switzerland He received M S and Ph D degrees in geodesy and geodynamics from ETH Zurich DONAT PERLER is a Ph D candidate at ETH Zurich He received an M S degree in computer science from ETH Zurich ALAIN GEIGER is a professor in the Geodesy and Geodynamics Lab of the Institute of Geodesy and Photogrammetry at ETH Zurich He received an M S degree in physics and a Ph D in geodesy and geodynamics both from ETH Zurich HANS GERT KAHLE is professor emeritus of geodesy and geodynamics at ETH Zurich and was leader of the Geodesy and Geodynamics Lab from 1979 to 2009 He received a Ph D degree from the University of Kiel Germany and the habilitation in geophysics from ETH Zurich MORE ONLINE Further Reading For references related to this article go to gpsworld com and click on Richard Langleys Innovation under Inside GPS World in the left hand navigation bar 2010 CORPORATE PROFILES Buyers Guide Available Online Featuring 152 GNSS Companies Over 100 Product Categories Search Companies and Product Categories with the Click of a Button The Only Industry Reference for Manufacturers and System Integrators 2 New Product Categories Software Geotagging Accessories Other WWW GPSWORLD COM 2010BUYERSGUIDE www gpsworld com July 2010 GPS World 47