NEXRAD Data Quality: The AP Clutter Mitigation Scheme

Atmospheric conditions favorable for refraction of the radar beam can produce additional ground clutter return, called anomalously-propagated (AP) return. This AP return is a contaminant within the radar base data fields that causes erroneous estimates of rainfall accumulation, among other artifacts. Within the current WSR-88D quality control system, AP clutter return is removed by manual application of additional clutter filters. Automation of clutter filter control is a desired goal of the AP Clutter Mitigation Scheme. The AP Clutter Mitigation Scheme is a planned implementation within the WSR-88D Open Radar Product Generator (ORPG) and the Open Radar Data Aquisition (ORDA). The AP Clutter Mitigation Scheme has four parts: the Radar Echo Classifier (REC), the Reflectivity Compensation Scheme (Z-Comp), Clutter Filter Control, and Tracking of AP Clutter. Research efforts to date have concentrated on the REC and Z-Comp.

The Radar Echo Classifier (REC) uses fuzzy-logic techniques to determine the type of scatterer measured by the WSR-88D. Currently, three algorithms have been designed and tested: the AP Detection Algorithm (APDA) defines anomalously-propagated (AP) ground clutter return, the Precipitation Detection Algorithm (PDA) determines convective and stratiform precipitation regions, and the Clear Air Detection Algorithm defines return from insects in the boundary layer. These algorithms have been developed using data from WSR-88D systems and from the NCAR S-Pol radar. Results will be presented.

The Reflectivity Compensation Scheme (Z-Comp) uses a Gaussian approximation for precipitation spectra and a simulated WSR-88D clutter filter to estimate the correction necessary to offset the clutter-filter-induced bias in the reflectivity. Output from the REC will determine where the Z-Comp method is applied such that only regions of precipitation are compensated. The Z-Comp method has been tested using WSR-88D time-series data (Archive 1) collected at the Memphis (KNQA) WSR-88D. Results will be presented.

Implementation of the Radar Echo Classifier was achieved on the NCAR S-Pol radar during real-time operations of the STEPS field program in July 2000. Implementation of the Z-Comp algorithm is underway for real-time operations of the IMPROVE field program to be held in January-February 2001. Operational use of the AP Clutter Mitigation Scheme is desired since this allows refinements to be made quickly. Preliminary results from these implementations will be presented.