"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?


As I read it, Not exactly, but sort of. Depends on your definition of
"composited".

Based on NOAA's description, Composite is just *the strongest* of the echoes
from the scans at many elevations. In other words, the radar scans the
entire 360 degree azimuth scan at several elevations, say 0.5 degrees above
the horizon, 1.5 degrees above the horizon, 2.5, and 3.5, etc. etc.
Apparently up to 14 such different elevations may be used up to 19.5 degrees
above the horizon. What is displayed on the map is the *strongest* echo of
all of those scans. In some areas of the map the strongest echo may be from
the 1.5 degree scan, in another it might be from the 3.5 degree scan, etc.
hence *composite*. This would presumably assure you that the echo you see,
is the "most intense" echo of the storm in that area, no matter what height
it actually came from.

But the multiple scans (and the image processing) all take time, so the
images are updated only every 5 or 6 minutes.

Although their description makes it clear that "Base" reflectivity is the
display from just ONE scan (therefore it will not guarantee that you are
seeing the strongest reflection), but they did not say what at *what
elevation* that scan is normally done, or whether a "base" display is shown
for EVERY scan.