Multiparametric radar/microwave precipitation retrieval

The use of polarisation difference over the land for three cases of different nature has been investigated: Poldirad (14/07/1997, strong convective event), Graz (10/07/1997, convective event) and Chilbolton (27/06/1997, stratified event). The correlation between vertical and horizontal polarisation Tbs differences at 85 and 19 GHz and ZH and ZDR as measured by the available radar has been evaluated. The radar domain has been classified in three rain classes by means of the ZH values: no rain (0<ZH<20 dBZ), moderate rain (20<ZH<30 dBZ) and heavy rain/hail (ZH>30 dBZ). It was found that the 19 GHz polarisation differences decrease when Zdr increase. On the contrary, 85 GHz channels Tb differences are not related to Zdr variations. At 85 GHz the increase of Zdr results in an average increase of the polarisation difference from the satellite; this implies a rather strong correlation between the rain layer at the ground (as seen by radar) and the ice layer on the top of the cloud as seen at 85 GHz.