Objective Determination of Quality Parameters and Clutter Filter Number for Operational S-band Dual-Polarization Radar

The quality of moment data from an operational dual-polarimetric weather radar can be optimized by the selection of proper values for quality parameters(e.g., Signal Quality Index (SQI), Clutter Correction (CCOR), SIG, and LOG) and clutter filter (e.g., Infinite Impulse Response (IIR) and Gaussian Matched Adaptive Processing (GMAP)) in the signal processing. As the number of the filter and threshold of quality parameters increase to reduce ground clutter and noise, the meteorological echoes are gradually diminished as well. The objective determination of the optimal filter number and threshold values is the key in routine radar operation. However, they are subjectively determined by the experts of most of operational weather radars.

We aim to propose the new approach to determine the optimal number of IIR filter and SQI threshold for an operational Doppler weather radar. In this study, two special scan strategies were designed for the test of IIR filter and SQI using S-band dual-polarization radar at Yong-In testbed, respectively. For the sensitivity test of IIR filter, the filter number was changed from 0 (=no filter) to 15 while all other quality parameters set to zero. The SQI threshold was examined by changing the threshold from 0% to 80% with an interval of 2% while the IIR filter and all other quality parameters (e.g. LOG, CCOR, and SIG) set to zero. By applying different number of IIR filter and SQI threshold, the filtered echo area on the ground clutter and noise region was calculated while the unfiltered area on meteorological region was investigated. For determination of optimal values, Critical Success Index (CSI=H/(H+M+F)) was utilized. H (or M) is the number of filtered (or unfiltered) echo over ground clutter and noise area, F (or C) is same as H (or M) except for meteorological echo area. The optimal SQI thresholds and IIR filter number were objectively determined based on CSI.

According to CSI, the optimal SQI thresholds were 30%, 50%, and 60% and the optimal numbers of IIR filter were 8, 7, and 6 at the elevation angles of 0.2°, 1.12°, and 2.81°, respectively. The number of IIR filter decreases while SQI threshold increases with increasing elevation angles. The results are in accord with decrease of ground clutter and increase of noise in radial velocity with increasing the elevation angles. We can conclude that the proposed method is helpful to determine IIR filter number and SQI thresholds objectively. The proposed method can be applied to other filter (e.g. GMAP filter) and other quality parameters (e.g. LOG, SIG, and CCOR).