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    Re: dip, dip short, distance off with buildings, etc.
    From: Marcel Tschudin
    Date: 2006 Jan 6, 14:07 +0200

    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

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