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1. Introduction
Accurate rainfall estimates are crucial for numerous applications in hydrology, nowcasting, and mesoscale model validation. Ground-based operational weather radar networks are currently considered the only instruments capable of providing the requested high-resolution (1 km2) and frequent (5 min) precipitation fields over mesoscale or even synoptic areas. The density of automated rain gauge networks is in general too scarce, especially in complex terrain, to yield the same space–time coverage of precipitation systems. On the other hand, rainfall estimation from satellite-borne instruments (radiometers or radars) is still an open field of research and does not fulfill as of yet the above-mentioned user’s needs. The forthcoming Global Precipitation Mission will probably open new perspectives but it is likely going to take another decade or two before operational products become available.
While radars were recognized early on as key tools for monitoring the structure and evolution of precipitating systems, the correct understanding and assessment of the various error sources are more recent. Errors affecting the measurements of rainfall by radars can be grouped into three categories (Zawadzki 1984; Joss and Lee 1995; Dinku et al. 2002): 1) errors related to the radar system itself (radar hardware calibration, errors in the azimuth and elevation angles), 2) errors related to the interaction between the radar wave and the environment (ground clutter or biological targets, clear-air echoes, partial beam blocking, partial beam filling, attenuation by rain, filtering along the vertical due to beam broadening with range), 3) errors occurring when converting instantaneous radar reflectivity plan position indicators (PPIs) into surface rainfall accumulations [nonuniform vertical profile of reflectivity (VPR), wave propagation fluctuations, precipitation type, Z–R relationship, precipitation drift, advection of rain patterns]. The present paper reports on the development of the new French operational radar rainfall estimation algorithm that purports to correct radar data for ground clutter (GC), partial beam blocking (MSK), VPR effects (VPR), and advection (ADV). Radar hardware and pointing angle calibration procedures are not considered in this paper [see Tabary (2003) for more information on that]. Likewise, as all 18 French operational radars are conventional ones, departures from the Marshall–Palmer Z–R relationship (Z = 200R1.6) and attenuation by rain are not corrected for. Polarimetry appears to be a...