"Brian Salt" wrote in message
k.co.uk...
When the wind
blows hard it is really rough up there, so any balloon launch would be
near horizontal. Would they bother in such wind conditions, I wonder?

... no, not if it is really blowing a gale - because under most events of
such, the cloud base would be too low to allow useful work. However,
there will be marginal occasions when it will be useful to have the
option of positioning the theodolite differently.

Martin.

In article ,
(Martin Rowley) wrote:

I have a couple of photographs here (in old publications of the time)
which show the operation of pilot balloon equipment - don't know how
well they would scan, but if you are interested, let me know and I'll
have a go sending them on.

Forgot to comment on your offer. If you could scan them I'd be interested
to see them. With my Epson scanner, I find it better to scan photographs
from publications using 'Illustration' as the type, with de-screening
switched on. Yours might be different!

Thanks.


Brian Salt.
Remove NS from address before replying.

Brian Salt wrote:

angle to find the height? Or would the use of two theodolites
simultaneously, spaced at about 22 feet apart, allow the height to be
found without needing the horizontal distance?

I didn't try to read the entire thread, so someone else may have
answered already.

A balloon's position is specified by three variables -- e.g., height,
horizontal range, and azimuthal direction (substitute x and y position
for the last two, if you prefer).

A single theodolite measures only two independent variables (azimuth and
elevation angle), so you'd need to supply a third (height or range) in
order to determine the position of the baloon in 3-space.

Two theodolites separated horizontally by a sufficient distance supply
up to four measurements. If you toss out one, you can use the remaining
three to solve for the balloon's position. Which one you should toss
out depends on where the balloon is. Under circumstances (e.g., the
balloon is on the horizon AND aligned with the two theodolites), even
two theodolites won't give you enough independent information to
uniquely solve for the balloon's position.

--
____________
Grant Petty
University of Wisconsin-Madison
Browse my new book "A First Course in Atmospheric Radiation"
at http://www.sundogpublishing.com/AtmosRad.htm

In article ,
(Grant) wrote:

I didn't try to read the entire thread, so someone else may have
answered already.

That's understandable!

A balloon's position is specified by three variables -- e.g., height,
horizontal range, and azimuthal direction (substitute x and y position
for the last two, if you prefer).

A single theodolite measures only two independent variables (azimuth
and elevation angle), so you'd need to supply a third (height or range)
in order to determine the position of the baloon in 3-space.

Which is where I came in, not realising that, in practise, the azimuth and
elevation are measured at (usually) 1 minute intervals. The height of the
balloon in known, since the rate of rise is 'constant' because its weight
is set before launch.

So a second theodolite is not actually required to do the job.