Quantitative Analysis of the Performance of Spatial Interpolation Methods for Rainfall Estimation Using Commercial Microwave Links

Using signal level measurements from commercial microwave links (CMLs) has proven to be a valuable tool for near-ground 2-D rain mapping. Such mapping is commonly based on spatial interpolation methods, where each CML is considered as a point measurement instrument located at its center. The validity of the resulted maps is tested against radar observations. However, since radar has limitations, accuracy of CML-based reconstructed rain maps remains unclear. Here we provide a quantitative comparison of the performance of CML-based spatial interpolation methods for rain mapping by conducting a systematic analysis: first by quantifying the performance of maps generated from semi-synthetic CML data, and thereafter turning to real-data analysis of the same rain events. A radar product of the GermanWeather Service, serves as ground truth for generating semi-synthetic data, in which several temporal aggregations of the radar rainfall fields are used to create different decorrelation distances. The study was done over an area of 225X245 km2 in southern Germany, with 808 CMLs. We compare the performance of two spatial interpolation methods - Inverse Distance Weighting and Ordinary Kriging - in two cases: where each CML is represented as a single point, and where three points are used. The points’ measurements values in the latter are determined using an iterative algorithm. The analysis of both cases is based on a 48 hour rain event. The results re-confirm the validity of CML-based rain retrieval, showing a slight systematic performance improvement when an iterative algorithm is applied so each CML is represented by more than a single point, independent of the interpolation method.