Ground Clutter

"Ground clutter" occurs when radar side-lobes bounce off objects and the ground in the vicinity of the radar.  Most of the ground clutter echoes are stationary (since objects on the ground are not moving) and can be filtered out by NEXRAD "declutter" algorithms so it is not seen by users.  However, there are always some echoes which do not have coherence from one scan to the next which show up even though the declutter algorithm is being applied.

 Therefore, ground clutter has a different appearance than precipitation echoes which are contiguous and have spatial coherence. Ground clutter usually has a somewhat speckled appearance and changes from scan to scan.

Ground clutter usually shows up more strongly in clear-air mode than in precipitation mode, because clear-air mode is a more sensitive level of operation.

Using GARP, examine areas of ground clutter in both precipitation mode and clear-air mode:

Precip. mode:

1. First, using a browser, click on the national radar mosaic for the U.S.

2. Click on an area with precip. in range of the station, but not actually at the radar site.

3. Find the three letter identifier for that radar, and display it in GARP.

You should see coherent areas of precip. moving through the radar range, and also a bluish or greenish "speckled" area in the vicinity of the radar itself.  The speckles tend to "sparkle" as the loop progresses.

Clear-air mode:

1. First, using a browser, click on the national radar mosaic for the U.S.

2. Identify an area far from precipitation areas.

3. Find the three letter identifier for a radar operating in clear-air mode.

You should see a reddish-orange (and sometimes all different colors) "speckled" area in the vicinity of the radar itself.  The speckles tend to "sparkle" as the loop progresses.