Moving clutter spectral filter for Terminal Doppler Weather Radar

Detecting low-altitude wind shear in support of aviation safety and efficiency is the primary mission of the Terminal Doppler Weather Radar (TDWR). The wind-shear detection performance depends directly on the quality of the data produced by the TDWR. At times the data quality suffers from the presence of clutter. Although stationary ground clutter signals can be removed by a high-pass filter, moving clutter such as birds and roadway traffic cannot be attenuated using the same technique because their signal power can exist anywhere in the Doppler velocity spectrum. Furthermore, because the TDWR is a single-polarization radar, polarimetry cannot be used to discriminate these types of clutter from atmospheric signals. In order to mitigate this problem, we developed a moving clutter spectral filter (MCSF). Operating in the two-dimensional (2D) range-Doppler domain, the MCSF works in several steps. First, we detect and eliminate “point” targets in range in the 2D spectrogram. This step gets rid of isolated Doppler signatures that are often generated by a bird or a compact flock of birds. Second, we determine the number and location of modes (statistical peaks) in the spectrum at each range gate. This step involves joining spectral peaks that are deemed statistically indistinguishable through a number of criteria such as the normalized excess mass statistic. Third, one mode is chosen at each range gate (if there are two or more modes) based on the “shortest total path” in range from the first to last range gate. The “distance” between gates is determined by the circular spectral frequency difference between a mode in one gate and a mode in the next gate. Finally, for each gate with multiple modes, the ones that were not selected are eliminated. This method does not necessarily penalize sharp range gradients in the first moment, but rather rewards overall continuity in range. It is effective in retaining a spectral feature with global continuity in range (wind field) over a coexisting spectral signature with only local continuity in range (bird flock “burst”). This algorithm is undergoing preliminary testing off line; we are planning real-time implementation and testing on an operating TDWR in 2010.

*This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.