Polarimetric Rainfall Retrieval from a C-Band Weather Radar in a Tropical Environment (The Philippines)

摘要

We evaluated the potential of polarimetric rainfall retrieval methods for the Tagaytay C-Band weather radar in the Philippines. For this purpose, we combined a method for fuzzy echo classification, an approach to extract and reconstruct the differential propagation phase, Φ_(DP), and a polarimetric self-consistency approach to calibrate horizontal and differential reflectivity. The reconstructed Φ_(DP) was used to estimate path-integrated attenuation and to retrieve the specific differential phase, K_(DP). All related algorithms were transparently implemented in the Open Source radar processing software wradlib. Rainfall was then estimated from different variables: from re-calibrated reflectivity, from re-calibrated reflectivity that has been corrected for path-integrated attenuation, from the specific differential phase, and from a combination of reflectivity and specific differential phase. As an additional benchmark, rainfall was estimated by interpolating the rainfall observed by rain gauges. We evaluated the rainfall products for daily and hourly accumulations. For this purpose, we used observations of 16 rain gauges from a five-month period in the 2012 wet season. It turned out that the retrieval of rainfall from K_(DP) substantially improved the rainfall estimation at both daily and hourly time scales. The measurement of reflectivity apparently was impaired by severe miscalibration while K_(DP) was immune to such effects. Daily accumulations of rainfall retrieved from K_(DP) showed a very low estimation bias and small random errors. Random scatter was, though, strongly present in hourly accumulations.