Cloud Vertical Profile Analysis through Active and Passive Microwave Data

This paper reports the experimental fusion of ground based radar and satellite radiometer data in order to analyse cloud vertical profile structures, and their influence on passive microwave signature. Satellite passive microwave measurements of precipitation are characterised by the presence of large hydrometeors within clouds, they view the atmosphere from the top downwards and the spatial resolution is very poor. Surface-based radar measurements of precipitation are based on the estimation of hydrometeors falling from the basis of clouds; they view the atmosphere from the bottom upwards. The temporal and spatial resolution is very good. Vertical profiles obtained through polarimetric radar measurements carries a more complete information; such profiles provides useful clues to understand the vertical structure of observed phenomena and to aid the comprehension of the inversion topic passive microwave measurements. A research project is undertaken between active and passive microwave observation of precipitating clouds over land. In particular, the active microwave source is the Chilbolton radar, whilst the passive microwave source is the DMSP SSM/I instrument. The two microwave data type have been processed in order to be overlayable in time and space. Passive microwave data were processed in order to estimate several parameters related to cloud hydrometeors over land. Meanwhile, vertical profile radar data were processed in order to classify cloud hydrometeors types according to horizontal and the differential reflectivity values. A classification schema derived from Zrnic and Doviak was empirically calibrated and used to obtain cloud vertical profile structure. In particular three different layers were outlined: the bright band level, from the base of the cloud to the bright band layer and from the bright band to the top of the cloud layer. For each layer the percentage of wet and dry cloud particles was calculated. Once estimated the cloud vertical profile characteristics previously mentioned, scatterplots were worked out with SSM/I derived parameters along the Y axis and the radar derived cloud parameter along the X axis. The achieved analysis were numerous and complex. The developed research shows that radar vertical multiparameters profiles may be successfully utilised in order to estimate some cloud characteristics which are very important in order to better understand passive microwave brightness temperature behaviour. In particular, for rainfall monitoring over land, it is possible to notice the correlation between the high frequency brightness temperature range of values and the height of the top of the cloud. Furthermore, it is possible to appreciate the contribution of the wet particles belonging to the high layers of the cloud, to the brightness temperature at the high frequencies. Future work is including the assessment of the present results utilising a wider number of events and the introduction of parameters considering ground conditions.