Application of Multi-Scale tracking radar echoes scheme in QPN

A new radar echo tracking algorithm called MTREC (multi-scale tracking radar echoes by cross-correlation) is proposed in this paper to analyze movements of radar echoes at different spatial scales. Movement of radar echoes, in particular associated with convective storms, exhibits different characteristics at various spatial scales as a result of complex interactions among meteorological systems leading to formation of convective storms. For the null echo region, the usual correlation technique produces zero or very small magnitude of motion vectors depending on the prescribed size of echo region for computing correlation coefficients. To mitigate these constraints, MTREC is implemented using TREC (Tracking Radar Echoes by Correlation) technique with large “box” to determine the systematic movement driven by steering wind, and applying TREC technique with small “box” to estimate small-scale internal motion vectors. Eventually, the MTREC vectors are obtained by synthesizing the systematic motion and the small-scale internal motion. Performance of MTREC technique was compared with TREC technique using Khanun Typhoon on 11September 2005 observed by Wenzhou CINRAD/SA radar and a squall-line system on 23 June 2011 detected by the Beijing CINRAD/SA radar. The results demonstrate that more spatially smoothed and continuous vector fields can be generated from MTREC leading to improvements in tracking the entire radar reflectivity pattern. The new multi-scale tracking scheme was applied to study its impact on the performance of quantitative precipitation nowcasting (QPN). The location and intensity of heavy precipitation at the lead time of 1 hour was found to be more consistent with quantitative precipitation estimate using radar and rain-gauges.