Mxsmanic wrote in
:

buttman writes:

Theres a little "eye" that looks up at the sky at various points. It
detects if there is cloud, or sky. The sensor is prone to errors,
though. Sometimes if it's broken, it'll say its overcast because some
of the sensors are pointing diagonally and are sensing the side of
the cloud. I had an ATC college-style text book that had a very
informative diagram of how they worked, but that book is long gone.

http://www.cyanogen.com/products/cloud_main.htm

here is an example of one.

Cool--I wouldn't mind having one (useful for photography as well as
astronomy and aviation). However, it's still a ground-based sensor,
so it would only see the first level of clouds. Conversely, a
satellite would only see the top layer of clouds. If there are three
or four layers of clouds, how do weather services discover them?

The same is true for temperature, humidity, and pressure. Pressure
you can probably infer from surface pressure, and temperature you can
guess at in a similar way. Humidity is more vague. I'm curious as to
how all of these get measured aloft.

And what about winds? Weather services seem to have awareness of
winds aloft, but where are they getting the measurements? Winds aloft
may have no correlation with surface winds and can change a lot over
short distances. You could set up probes, but that's a lot of probes
to launch and recover even to cover small areas. You could rely on
PIREPs, but that seems kind of hit and miss. So how is it really
done?

Send me $300 and I'll tell you.


Bertie