Real-time rainfall maps based on satellite broadcast signal attenuation

In spite of the variety of existing methods to measure precipitation, the retrieval of rainfall fields is still a matter of research, because of the high number of applications in different fields critically dependent on rainfall data and thus demanding for upgraded precisions in quantity estimation, spatial distribution and resolution, as well as for homogeneous retrieval over large domains. Telecommunication technologies can bring relevant information on rainfall rate, through the measurement of the attenuation caused by raindrops on broadcast satellite signals, albeit not specifically developed for this. NEFOCAST is a FAR-FAS research project funded by Regione Toscana, which exploits this feature through innovative two-way (i.e., transmit/receive) devices named Smart Low-Noise Block converter (SmartLNB), that are going to constitute a free-of-charge network of sensors, densely distributed in urbanised areas. Usage of smart LNBs has many advantages in terms of cost and setup and has a great potential for application worldwide including areas lacking of meteorological data, providing also an efficient data transmission solution. In NEFOCAST an experimental network of SmartLNBs has been deployed in Florence and analysed through a co-located rain gauge network and a Doppler polarimetric X-band radar for cal/val objectives. The high rate of attenuation measurements provided by the SmartLNBs (in our case 1 min.), suggests to approach the rainfall retrieval problem similarly to a trajectory assessment in a phase space, using a Kalman filter to achieve the rainfall field over a target domain. SmartLNBs provide an average measurement along a non-nadir path, so that information on the structure of the intercepted rainfall system are needed to retrieve ground precipitation, and MSG satellite observations can be used at the purpose. In this work we will present the measurement concept, the signal processing algorithm, and the method to estimate the rainfall fields. Firstly, some significant synthetic case studies will be introduced, featuring some events with different precipitation patterns; then, real SmartLNB measurements, acquired during different meteorological conditions, will be discussed, analysing also the impacts of SmartLNB density, satellite link geometry and structure of rainfall systems.