Traditionally, operational use of X-band radars was abandoned because of the strong attenuation they suffer in presence of rain. However several groups in the world have revisited lately the idea of using X-band as a hydrological sensor. The reason is that new techniques based on polarization diversity offer a way to overcome the problem of attenuation. Because they are relatively small and cost effective, X-band radars represent an attractive solution for filling critical gaps in the coverage of operational radar network and providing fine scale observations of precipitation above mountainous region or urban basin. A X-band polarimetric radar (X-port) is developped in our group. Research activities are being developped arround this project to assess the practical feasability of various algorithms which have been proposed in recents years. The quality of rain estimate expected from the various methods is also investigated.

A comparison of various algorithmes, all based on polarisity diversity and with or without the use of differential phase shift , will be presented. The results are based on a few observations and also to extended simulations. The senstivity of rain estimates to drop size and shape distributions is envestigated together with measurement accuracy and sampling effects. The simulation set up and its limitations will be explained. The problem of parameter tuning, from independant measurements or based on self consistency of radar data itself, will also be discussed, in the presentation.