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Tomography sensitivity tests and comparisons of water vapor fields with radar data.

Reverdy Mathieu

As part of the OHM-CV (Observatoire Hydrométéorologique Méditerranéen Cévennes-Vivarais) an extensive GPS project has collected data during the autumn periods of 2002 to 2006, located in the south of France. In particular, a dense GPS network (16 stations over a 30 km by 30 km area) was deployed in the Cévennes-Vivarais region.
In order to retrieve the 3-D water vapour distribution, we have developed a GPS tomographic inversion software based on the LOFTT-K algorithms from LDL.
From the GPS observations, we derive the integrated water vapour and estimate the slant integrated water vapour that is the primary input for the tomographic inversion. In addition, using synthetic data, we will study the effect of the network geometry as well as the numbers of inputs (SIVW) in order to test the sensitivity of the tomographic algorithm and better understand its limits.
Rain data are provided by the Bollène Météo France radar operated in a 3-D volume scan mode. The resulting data display the rain reflectivity over the same area that the GPS network for comparison and further correlations. In addition, we use rain gauges data to complement the radar data on the ground.
One of our objectives will be to link the water vapour distribution and its dynamics to the occurrence of sustained precipitations.