Weather radar signal processing techniques

Ground Clutter Detection and Filtering for Weather Radars
The CLEAN-AP© filter

Example of clutter suppression exhibited by the CLEAN-AP© filter. Note that the filter provides over 60 dB of clutter suppression without biasing the weather signal power estimate. To place this into context, the filter easily provides the clutter suppression requirements of 50 dB required for operations in the U.S. network of weather surveillance radars (i.e., the NEXRAD network of WSR-88D radars). Image courtesy of D. Warde.

A common dilemma in obtaining quality meteorological-variable estimates using Doppler weather radar is the application (or misapplication) of ground clutter filters (GCF) to mitigate contamination from ground returns. Typically, weather radars use static clutter maps (i.e., pre-identified clutter contaminated regions) to control the application of the GCF. Ideally, the GCF should only be applied if the ground clutter contamination obscures the weather estimate. However, the problem of applying the GCF becomes very complex considering the dynamic atmospheric effects on radar beam propagation. The goal of this project is to develop efficient techniques that provide both automated detection and application of ground clutter filtering.

Recently, we suggested a spectral technique for automatic detection and mitigation of ground clutter contamination: the Clutter Environment Analysis using Adaptive Processing (CLEAN-AP©) filter. We have shown the clutter detection and mitigation performance of the CLEAN-AP© filter using time-series data from the National Weather Radar Testbed Phased-Array Radar (NWRT PAR), the national network of weather surveillance radars (WSR-88D), and the University of Oklahoma's OU-Prime radar . Compared to current technologies used for ground clutter suppression, the CLEAN-AP© filter provides a real-time, integrated clutter mitigation solution with:

  • improved ground clutter suppression,
  • effective ground clutter detection, and
  • dynamic ground clutter suppression characteristics optimally matched to the existing atmospheric environment. All of this is achieved with modest computational complexity and increased quality of meteorological estimates.

In March of 2011, the NEXRAD Technical Advisory Commitee approved CLEAN-AP for an engineering evaluation on the WSR-88D. In the near future, our plan is to enhance the detection capabilties of CLEAN-AP© by using polarimetric information available from this system. In addition, we have extended this filter to work with staggered PRT sequences.

For more details about CLEAN-AP©, follow this link to get a copy of the paper that we presented at the 2009 AMS Radar Conference in Williamsburg, VA . Comparisons between CLEAN-AP© and the current ground clutter mitigation scheme on the WSR-88D were presented in a paper at the 2010 AMS Annual Meeting. In addition, we have filed an Invention Disclosure with The University of Oklahoma Intellectual Property Office; the non-confidential details about this technique can be found in this document.

Our latest report to the NWS Radar Operations Center documents the work that resulted in the endorsement of CLEAN-AP by the NEXRAD Technical Advisory Committee.

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