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    Re: Astronomical Refraction: Computational Method for All Zenith Angles
    From: Marcel Tschudin
    Date: 2005 Aug 22, 17:40 +0300

    Refering my last mail, where I mention that I can not reproduce the values
    shown in the Auer Standish paper using the polytropic atmosphere model:
    1) I overlooked the part on the following page: "These values are used to
    compute the coefficients for only that associated region of the atmosphere.
    In order to ensure continuity, the temperature and the density must be
    extrapolated to the boundary, defined by the altitude hB."
    2) When introducing what is described there, the results are even worse.
    It seems that there is something wrong in my stratospheric part. May I ask
    you, Frank, to have a look at it? May be you can see what is going wrong
    Thanks, Marcel
    Function getmu (r : Real): Real;  // r = REarth + h
    begin  // getmu
    // Poytropic atmospheres:
    Tw:=273.15+RefTemp;       // Tw=Temperature at reference point in ?K
    RHOw := 273.15/1013.25 * RefPress/Tw;   // RefPress = Pw
    Rw := (REarth+RefHeight)/REarth;        // RefHeight = hw
    Rrel := r/REarth;           // r relative to REarth
    rr := 1.0/Rrel - 1.0/Rw;
    // nPoly = Polytropic index = 5
    BETAw := g * REarth / ( Rgas * Tw * (1.0 + nPoly) );
    if R<=Rhb then
    begin                                                      // Begin:  T r o
    p o s p h e r e
    RHOpoly := RHOw * Power( (1.0 + BETAw * rr), nPoly); // Power(x,y)
    calculates x**y
    end                                                        // End  :  T r o
    p o s p h e r e
    begin                                                      // Begin:  S t r
    a t o s p h e r e
    Tb:=Tw * ( 1.0 + BETAw*(1.0/Rhb - 1.0/Rw) );
    RHOw := 273.15/1013.25 * RefPress/Tb;
    GAMMAw := g * REarth / ( Rgas * Tb );
    rr := 1.0/Rrel - 1.0/Rhb;
    RHOpoly := RHOw * EXP( GAMMAw * rr );
    end;                                                       // End  :  S t r
    a t o s p h e r e
    // Nminus1 ... Refractive index of air minus 1: (n-1)=0.00029241
    getmu := 1.0 + Nminus1 * RHOpoly;
    end;  // getmu

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