Satgen269    Unbending Satellite Signals   by GM4IHJ           21 May 94
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Uwe DL8OBF asks are there any notes about how to use doppler shift on
satellite signals to probe for dislocations/discontinuities in the
atmosphere. Yes there are in the RSGB Space Radio Handbook p141 to 143. If
you have an adio frequency meter and you take continuous records of
satellite downlinks, you can monitor both the normal doppler shift and,
shifts due to short term changes in the path by which the signal is coming
to you. 
Whilst your received signal dopplers slowly down in frequency as satellite
aspect changes with respect to your station, you will also see sudden
jumps in frequency caused by anomalies in the ionosphere and the
atmosphere which block one path and substitute another one at a slightly
different aspect/angle in its place . Noting that true downlinks are never
straight lines , they jump about in an irregular fashion determined by the
number of anomalies along the downward path. 
The difficulty is to decide which anomalies are due to the ionosphere and
which are due to the atmosphere, with the atmosphere being the culprit 4
times out of 5.
Visual Astronomers have the same problem when they look at light from a
star or a galaxy. After travelling thousands of light years almost
undisturbed, the last few hundred kilometers down to earth can be the site
of serious dislocations and disturbance. Hence of course the well known
"Twinkle Twinkle little star". The stars do not twinkle , the twinkle is
produced in the earth's atmosphere.
However,  astronomers recently had a lot of money to play with in a series
of "Star Wars" experiments, and a great deal of this money went on the
invention of highly successful "Adaptive Optics". This technique has the
telescope looking at two objects in its field of view. One is the
brightest star in the field, the other is the wanted weak star or faint
galaxy. Phase difference in the received light from the bright reference
star is used to drive high speed pistons behind the telescope lens ,
continuously altering its shape to maximise the in phase components of its
light, and hence greatly improving the instantaneous focus on the weak
target star , almost completely eliminating its "Twinkle".
A variant of this star wars lens bender, uses an earth based laser lined
up with the telescope. The telescope then monitors the bright laser
reflections from the discontinuities which exist in the ionosphere at
around 100 kms altitude, and use the received signal to bend the telescope
lens to maximise the quality of the received laser signal. Thereby ,
simultaneously improving the signal from the wanted target star or galaxy.
All these astronomical miracles are probably presently too expensive for
the average Radio Amateur to use to construct a radio version as opposed
to a light version of this idea. But there would seem to be no obvious
reason why modern electronics should not be used to monitor the reflection
of a powerful clear tone earth transmitted reference signal and use its
received components to auto correct the phase balance of a space diversity
field of radio antennas. Who knows, the technique may prove quite useful
for Radio Amateurs who want to work Mars QRP, in the next century.
Note.. The medical fraternity have been altering GM4IHJ's life style
rather drastically of late. So apologies to anyone who has yet to receive
an answer to a private query . Date for return of normal service is not
yet known. 73 de GM4IHJ @ GB7SAN