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    Re: Refraction near the Horizon ? Ob servation vs. Calculation
    From: Brad Morris
    Date: 2013 Apr 6, 15:10 -0400

    Marcel

    With all due respect ....

    You indicated that my pressure and temperature procedure is wrong. 

    I asked for you to show the procedure you use, with a worked example.

    You responded without a procedure.  The procedure is critical for understanding. 

    Put your procedure & numbers on a piece of paper.  Submit it to the group. 

    Brad

    On Apr 6, 2013 2:50 PM, "Marcel Tschudin" <marcel.e.tschudin---.com> wrote:

    Hi Brad,
    
    All your mentioned equations are approximations. It really depends on
    the accuracy one wants to achieve and whether this accuracy is really
    necessary or not. If one wants really to be exact, it is in this
    context actually not the radius of the earth which is of interest,
    it's rather the earth's radius of curvature at the location of the
    observer. Because the earth's shape is approximately an ellipsoid this
    radius of curvature depends on latitude and also on the azimuth,
    except at the poles. If you do not require this accuracy you can use
    any other less accurate mean earth radius which in the context of
    calculating dip are likely to be completely sufficient.
    
    Regarding the pressure and temperature dependency of refraction here
    some further explanations: The scaling factor (P/1010)/(T/283) adjusts
    the refactivity property of air, n, and as a consequence of it also
    the refraction resulting from it. However, the cause for light rays
    being bend in the atmosphere are temperature-GRADIENTS. The parameter
    k is introduced to describe in a simplified model the bended ray for
    terrestrial refraction and dip. From observations one obtained then
    typical values for it.
    
    Marcel
    

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=123390

       
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