A combined Micro-Rain-Radar (MRR) and weather radar system for improved real-time quantitative precipitation measurement (QPM)

Quantitative estimation of fallen precipitation at ground level using weather radar is hampered by numerous well documented problems: the variable relation between radar reflectivity and rain rate, a vertical evolution of rain intensity from ground to beam-height, attenuation, changes in water-phase, attenuation, and eventually insufficient temporal sampling. Extensive research has been done on the importance of these effects during the last decades, but solutions are hard to implement because of the difficulty to isolate each single effect during validation. The commonly used gauges and disdrometers have a very limited in-situ perspective which hardly gives information on the nature of the precipitation process or error sources on the scale of weather radar measurements.

The MRR-2, which is a low-cost vertically pointing Doppler radar, can estimate the drop size distribution assuming a relation between drop diameter and falling velocity, and thus give a better estimate of the current Z-R relation. The measurements also allow easy detection of the ice phase and the melting layer, and the measured vertical profiles may eventually be used to correct weather radar measurements. The use of dual radar measurements may also allow for the effective investigation of attenuation effects in both radars due to the high time resolution. Shifts in system gain commonly occurring in operational weather radar measurements can also be detected.

Currently a combined system of 2 MRRs and one X-Band Radar is operated by the Meteorological Institute of the University of Bonn in collaboration with hydrologists of mesoscale catchments within the range of the radar. Data transfer from the MRR is realized by internet connection** in near-real time with 1 minute intervals, transferring full information of the current drop size distribution, radar reflectivity, and estimated rain rate in 30 height intervals from 0 to 2000 meters, using a measurement interval of 15 seconds. A dense network of rain gauges provided by the hydrologists gives an excellent and independent source of validation.

** Real-time measurements publicly displayed at: http://www.meteo.uni-bonn.de/forschung/gruppen/mrr/index.html http://www.meteo.uni-bonn.de/forschung/gruppen/radar/index.htm