Application of X- and S-band radars for rain rate estimation over an urban area

The potential of ground-based radar systems operating at X-band for rainfall estimation over urban areas is investigated. To this end, rainfall measurements from the X-band weather surveillance radar SOLIDAR are compared against those from the colocated S-band research radar DARR and a line configuration of 4 tipping bucket rain gages located at ranges between 5 and 10 km from the radar site. The analysis is restricted to 1 rainfall event with a duration of approximately 2 h, a maximum instantaneous rainfall intensity of about 20 mm h^-1 and a cumulative rainfall amount of around 5 mm. Attention has been paid to a careful quality check of the data, particularly with respect to the effects of synchronization errors in the rain gage measurements and the effects of ground clutter in the radar measurements. It is demonstrated that the radar measurements compare well to each other, but that both radars fail to capture a rainfall peak observed by all rain gages. It is argued that this lack of agreement may be due to the fact that such local phenomena are lost in the radar data as a result of the fairly large amount of range averaging employed (600 m). This indicates that such resolutions, although necessary for achieving acceptable signal-to-noise ratios, may already be too coarse for urban hydrological applications. For the event considered the effects of attenuation on the X-band radar data are small.