Towards Improving the Clutter Mitigation Decision Algorithm in the WSR-88DP Radars

The Clutter Mitigation Detection (CMD) algorithm automatically detects ground clutter in real-time so that it can a clutter filter can be appropriately applied as the data are collected. The CMD is operational on the National Weather Service’s WSR-88DP radar network. The CMD uses the standard deviation of Zdr and PHIDP (SDZdr and SDPHI) computed over a radial segment of data. These local spatial standard deviation variables have proven to be very good discriminators between weather echoes and ground clutter. However it has been noted that the SDZDR and SDPHI increase with decreasing rhohv. Therefore, targets with intrinsically low rhohv, such as insect clear air and melting snow, are more difficult to differentiate from ground clutter than high rhohv echoes like rain and dry snow using SDZDR and SDPHI. False detections in clear air echoes are particularly problematic as they cause censoring errors in the SZ-2 phase coding algorithm. The fuzzy logic membership functions in CMD for SDZdr and SDPHI currently do not take this rhohv dependence into account and are setup to discriminate clutter from clear air echoes.

We are currently working towards developing membership functions that accounts for the dependence of SDZdr and SDPHI on rhohv. Two approaches are being tried. The first is to identify the presence of echoes that have intrinsically low rhohv and use separate membership functions for high and low rhohv echoes. The second is to implement dynamic membership functions that depend on measured rhohv. Early results indicate that increases in the probability of detection of clutter mixed with precipitation are possible in CMD without increasing false detections in clear air echoes. This presentation will describe the issue, the methods proposed and present the most recent results.