....back in Poland, all of us glider pilots allowed to fly had to go
through a very rigoreus medical examination. The Goverment could not
risk the investment of training the glider pilots without having the
option of eventally using them in Air Force. One of the medical test
was a stereoscopic distance evaluation. You would have to look at two
very small wooden sticks from a distance of five yards and the future
of your flying cariere was to be determinated by the simple guess...
which of them was closer?. No reference point was available. Without
going into details, I think the idea behind this test was to eliminate
the prospect pilots who couldn't, by natural instincts determinate the
distance to the object. Was there any merrit to such a test, I don't
know. All I know is that if we were not be able to determinate the
distance, we would have to be given by God only one aye.
rk


Roger Worden wrote:
I forget where I read this... but it seems to apply. An author pointed out
that it is very hard to estimate the size (therefore the distance) of
typical clouds because their borders are fractal. (A fractal is a line or
shape that has a fractional dimension. Wikipedia defines it as 'a shape that
is recursively constructed or self-similar, that is, a shape that appears
similar at all scales of magnification and is therefore often referred to as
"infinitely complex".') The little swirls of the cloud are shaped exactly
like the big parts. That means that you can't tell objectively whether the
curlicues that make up the cloud are "small and close" or "big and far".
When you get closer to a cloud, the details look just like the broader view.

So unless you have an object near the cloud to compare it to, such as a
mountain or an aircraft, it's tough to objectively estimate the cloud size
and therefore its height. Watch a typical Cu, estimate how big it is... then
be amazed at how big it REALLY is (and therefore how high or far it must be)
when an airliner flies in front of it. If there are clouds near the
mountains, sometimes you can estimate their size and altitude and then
assume the rest of the visible clouds are at a similar altitude.

A cloud's motion can be another clue... but only if you know something about
the wind. Is that cloud "big and far and moving fast" or "small and close
and moving slow" ?

The white-to-gray gradient can also be a clue if you can see the side of a
cloud.

Not sure if this helps... but it explains why it's hard!

Roger


"Papa3" wrote in message
ups.com...
A friend and I were driving back from the airport the other day. He
remarked, "Wow, cloudbase is high today. I bet it's at least 6,000
feet."

He and I began musing - exactly how do we know that cloudbase is high?
What visual cues tell us that the Cu are high (or low). We're not
talking Temperature Dewpoint spread here - strictly visual.

Any ideas?

And yes, flying season is obviously drawing to a close :-)

Erik Mann
LS8-18 P3