Exploring the use of mini-radars for high-resolution QPE in São Paulo – Brazil

Since December of 2014, the University of São Paulo (Brazil) is running 2 X-band mini-radar manufactured by ELDES as part of a resilience project. This project seeks the use of new and portable technologies that can be used to mitigate the effects of rain at small and median urban areas that are not cover by conventional weather radars. To test the effectiveness of this mini-radar technology in monitoring rain, the two mini-radars were installed 23 km apart under the coverage of a Dual Polarization S-band weather radar manufacture by Gematronik. To compensate the strong rain attenuation effects at 9.4 GHz, low transmitted power (10 kW) and large beam width (3 degrees), the mini-radars are configured with gate size of 90 meters (21.6 km range), 1 degree azimuth sample, antenna speed of 2 RPM, pulse width of 0.6 micro-seconds, PRF of 800 Hz and a MDS of -117 dB. As a result, this configuration could provide high-resolution rain characterization that can be used at different areas like: validation of satellite rain estimates, hydrological models, nowcasting, flash floods and etc. To explore the potentiality of such radars in estimating rain at high-resolution, we implemented a hourly QPE algorithm [Anagnostou and Krajewski, 1999] that combines radar reflectivity measurements from the 2 mini-radars with a network of 71 rain gauges. After adjusting the hourly Z-R relationships, daily rain accumulation maps are computed and compared with the Dual Pol SBand rain estimates [Ryzhkov et al., 2005]. The preliminary results based on March/2015 measurements shows differences that can reach up to 10-200% depending on the event. A remarkable min-radar sensitivity is observed at low rain rates that are not completely captured by the S-band radar due to its distance from São Paulo (~70 km). Furthermore, it is possible to identify small rain scale features that were not revealed by conventional weather radars. It is also important to notice that moderate rain above the radar radome is sufficient to attenuate more than 70% of the signal. Therefore, solutions need to be seek to avoid this problem. For the conference, more detailed information about the differences between the S-Band and the 2 mini-radars will be shown for the entire summer of 2014/2015. Additionally, the radome wetting will be explored to diagnose the attenuation loss. Finally, daily high-resolution rain maps will be compared with flooding street reports.