Errors and uncertainty in radar estimates of precipitation result both fromerrors in the basic measurement of reflectivity and from attempts to relatethis to the precipitation falling at the ground. If radar data are to beused to their full potential, it is essential that effective measures aretaken to mitigate these problems. The automatic processing of radar datathat forms part of the UK Met. Office's Nimrod system addresses a number ofspecific sources of error. These include the identification and removal ofspurious echoes resulting from anomalous propagation of the radar beam,errors resulting from variations in the vertical profile of reflectivity andradar sensitivity errors. Routine verification of the surface precipitationestimates has been undertaken, largely through comparison with rain gaugeobservations, over a range of timescales, which has allowed the benefits ofthe quality control and correction processes to be quantified. Although theimprovement derived varies according to the dominant synoptic situation, anaverage reduction in the root-mean-square difference between gauge and radardata of 30% can be achieved.