Doppler Filtering of Ground Clutter
Ground clutter is nothing more than unfiltered returns from stationary, and in some cases, not so stationary ground targets near the radar that contaminate radar products. It's general characteristics are:
- confined to the lowest elevation angles
- ranges are close to the radar
- present under most atmospheric conditions
The purpose of clutter filtering is to eliminate ground clutter without loss of precipitating areas. the method behind removing clutter is "if it doesn't move, it's not weather".
For clutter cancellation coherent hardware is needed along with simultaneous measurement of V and dBz and accurate setting of thresholds.
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Doppler filter (remove non-moving echoes)
- SQI (remove non-coherent echoes)
- clutter-to-signal ratio
- signal-to-noise ratio
Ground Clutter on Doppler Products
Radial velocities will be near-zero with some higher values present due to moving targets. The velocity estimates are power-weighted; high power is returned from stationary ground targets so clutter contamination biases velocity estimates toward zero. To see the influence of moving targets, long-term average maps are needed.
The influences of moving targets are there, but they may not be observable in individual radar images.
Example of heavily cluttered PPI image from the Vantaa radar in southern Finland. The Gulf of Finland runs west to east through the image.
The same image after clutter suppression.
Ground clutter on Spectrum Width Products
Low spectrum width with isolated higher values due to moving targets like highway traffic.
Static Masks
Static terrain masks can be used. In fact, the operational URP uses a static mask for the Strathmore radar (XSM) east of Calgary to filter out the Rocky Mountains for its MaxR product. It takes a static mask of the observed ground clutter and blacks out any/all echoes over these points. That mask is then used for thunderstorm cell identification.
URP Ground clutter Suppression
Static terrain masks can be used. In fact, the operational URP uses a static mask for the Strathmore radar (XSM) east of Calgary to filter out the Rocky Mountains for its MaxR product. It takes a static mask of the observed ground clutter and blacks out any/all echoes over these points. That mask is then used for thunderstorm cell identification.
URP Ground clutter Suppression
Basic reflectivity products have no ground clutter suppression. Doppler reflectivities do; echoes with zero radial velocity are filtered out.