# Real-Time Rain Rate Evaluation via Satellite Downlink Signal Attenuation Measurement
## 5 Experimental Results  
The rain rate sensing capability of NEFOCAST ground terminals featuring the SmartLNB device was assessed experimentally during spring 2017. Tests were carried out by monitoring a Ku-band downlink signal from EUTELSAT 10A satellite using a ground station identified as NEFOCAST-ITA-PI-003-X, which is located at the Department of Information Engineering of the University of Pisa, Italy. The main parameters and features of the satellite link are listed in Table 4. The SmartLNB continuously takes samples of the received signal and uses an embedded proprietary \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline \(k_{\text{B}}\): Boltzmann constant & \(1.38\times 10^{-23}\) J/K \\ \(T_{C}\): Cosmic noise temperature & 2.78 K \\ \(T_{G}\): Ground noise temperature & 50 K \\ \(T_{m}\): Mean thermodynamic temp. of the atm. formations & 265 K \\ \(T_{RX}\): Receiver noise temperature & 13.67 K \\ \(A_{atm}\): Gaseous atmospheric attenuation & 0.13 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters for the evaluation of \(E_{s}/N_{0}\). algorithm to evaluate the instantaneous \(\eta=E_{s}/N_{0}\), with 0.1 dB resolution. The update rate can be set by the user. During the experimentation, the samples of the received signal were processed every 20 s to measure the rain-induced attenuation affecting the received signal. Experimental calibration of the receiver in clear-sky conditions yielded \(\eta^{(Clear\,Sky)}=11.4\) dB. The rain height \(h_{R}\) was calculated as in (4), where the 0 \({}^{\circ}\)C isotherm height \(h_{0}\) was given by short-term forecasts issued by LaMMA Consortium (as the regional operational meteorological service of Tuscany Region) and the offset was set at \(\Delta h=400\) m. Parameters \(\alpha\) and \(\beta\) of the \(R\)-\(k\) algorithm were taken from Table 2, for the case of vertical polarization (forward link). These rain rate estimates, ultimately derived from the measurements of \(E_{s}/N_{0}\), i.e., of satellite signal quality, were eventually compared with the data provided by a conventional tipping-bucket rain gauge Davis PRO2 (0.2 mm resolution) co-located with the SmartLNB receiver. Figure 9 shows the plot of a real-time measurement of \(E_{s}/N_{0}\) obtained from a SmartLNB located in Pisa, Italy, 5-10 May 2017, while Figure 10 presents the corresponding signal attenuation, calculated from (8). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter/Feature** & **Value/Description** \\ \hline Satellite & EUTELSAT 10A \\ Longitude & 10\({}^{\circ}\) East \\ Elevation angle & 39.6\({}^{\circ}\) \\ EIRP & 48 dBW \\ Transponder Bandwidth & 36 MHz \\ Frequency & 11,345.833 MHz \\ Polarization & Vertical \\ Receiver Antenna Diameter & 75 cm \\ LNB Noise Figure @ 290 K & 0.2 dB \\ Physical Layer Protocol & DVB-S2 \\ Symbol Rate & 29.00 MBaud \\ MODCOD & QPSK 4/5 \\ \hline Ground Station Coordinates & 43.72031\({}^{\circ}\) North \\  & 10.38377\({}^{\circ}\) East \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Features of the satellite link used to test the rain sensing system. Figure 9: \(E_{s}/N_{0}\) provided by the SmartLNB in Pisa, Italy, 5-10 May 2017. We now focus on a few significant rain events which occurred in Pisa on 6 May and 9 May 2017. On both days, LaMMA's short term forecasts indicated that the 0 \({}^{\circ}\)C isotherm height was \(h_{0}\cong 2.4\) km. Figure 11 is relative to the rain event which occurred on 6 May and compares the rain rate estimated every 20 s by the NEFOCAST system (solid line) with the estimates provided every 5 min by the TBR (dashed line), according to the following formula  
\[\hat{R}=\left(\frac{n_{tips}\cdot\Delta|_{\mathrm{mm}}}{5\,\mathrm{min}} \right)\cdot 60\,\frac{\mathrm{min}}{\mathrm{h}}, \tag{10}\]  
where \(\Delta|_{\mathrm{mm}}=0.2\) mm is the tipping resolution, i.e., the measured rainfall per tip, and \(n_{tips}\) is the number of tips counted in a 5-min interval. Figure 11: Pisa, 6 May 2017.