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First: Happy New Year to all of you!

> ..... Then to include refraction, you  simply change the
> radius of the Earth from R to R/(1-x) where x depends on the  temperature
> gradient
> of the atmosphere. On average it's about 0.15 but it can  easily be
> anywhere
> in the range 0.13 to 0.17 and sometimes it's as low as 0 or  as high as
> 1.0
> (temperature inversions yield higher values of x).


Yes, I am still working on refraction and dip...

I had a contact with a professor at the ETH (Federal Institute of
Technology) in Zurich. He mentions that the value of 0.13 with a standard
deviation of plus/mines 0.06 (as mentioned in a surveyors software LTOP
http://www.swisstopo.ch/download/geo_software ) is only valid in high
mountain areas and also there only by exception under certain conditions.
Further on, he indicates that there does not exist a fixed value and is
warning to use this value at all. He indicates that the terrestrial
refraction depends on the thermal radiation of the earths surface which is,
for a location and time, so much variable, that it even may change the sign
in case of inversion.

On the other hand, first provisional results of my investigation indicate
that it seems to be possible to reproduce the famous values around the 0.13
by using the most likely (mode) temperature profiles of  balloon sounding
data, this by iteratively finding the value for the dip for an observer at a
given height and by calculating the terrestrial refraction from the dip by a
geometrical relationship. I will inform you as soon as the final results are
available.

Marcel

   

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