Bias adjustment of radar-based 3-hour precipitation accumulations

In this technical report it is demonstrated that the quality of the 3-hour accumulation product can be significantly enhanced by a straightforward gauge adjustment procedure. The KNMI network of automatic rain gauges is used for this real-time adjustment. The impact of the compositing algorithm on the quality has been assessed and a processing scheme for operational implementation is presented. The quality of the bias-adjusted 3-hour accumulation products is evaluated using both ``dependent'' and ``independent'' observations. A 6-year dataset of bias-adjusted accumulation products between 2000 and 2005 was used for the verification. It is concluded that the proposed scheme effectively removes the mean-field bias from the raw accumulation products and that it substantially reduces the standard deviation. Therefore it is highly recommended to add the bias-adjustment procedure to the operational 3-hour accumulation product.