Base reflectivity versus composite reflectivity

"Jay Beckman" wrote in message
news:kowie.10549$Fv.335@lakeread01...
In light of the fact that summer thunderstorm activity is coming quickly
(and our traditional "monsoon" season) here in the desert, this subject is
very interesting.

In reading the descriptions of "Base" vs "Composite" at the NWS website,
am I taking away the right idea:

Base: Image derived from a single radar azimuth
Composite: Image derived from multiple radar azimuths then, well,
composited into one 2D top-down view?


Well... from multiple radar elevations, not azimuths. The radar makes its
sweeps through the full 360-degrees of azimuth.

The radar processing system creates a "volume scan" from multiple 360-degree
azimuth scans at different elevation settings... 0.5 degrees above horizon,
then 1.5 degrees above horizon, 2.5, 3.5, etc. According to their
description, up to 14 such full-circle scans can be made, apparently from
0.5 up to 19.5 degrees above horizon.

The "composite" display, simply displays the strongest echo at any
particular point on the map, chosen from those 14 scans. Repeat for every
single pixel on the map.

Note that doing 9 or 14 circles with the radar antenna... plus the computer
processing to arrange the display... all take some time, so the composite
display is updated only every 5 or 6 minutes.

The "base" scan is the display from a single 360-degree scan at 0.5 degrees
above the horizon. So the farther away from the radar site, the higher
above the surface from which the echoes are displayed.

Those "volume-scans" can be computer-processed for other purposes, such as
determining max tops... which would help indicate the location of the most
severe storms.