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    Re: dip angle refraction correction
    From: John Huth
    Date: 2011 Dec 2, 17:48 -0500
    Nevermind - answered my own question - great website and I should've known because others had pointed this out to me before.


    http://mintaka.sdsu.edu/GF/explain/atmos_refr/altitudes.html

    On Fri, Dec 2, 2011 at 5:35 PM, Apache Runner <apacherunner@gmail.com> wrote:
    I have a somewhat esoteric question, but I thought I'd pose it to the list to see if anyone knew of a program or website that could do this.

    Here's the situation - some students are doing a final project where they went to the tallest building in Boston and used a water level to establish a horizontal and then sighted down to the horizon.   They then had measurements of the height of the building and want to turn this into a curvature of the earth. 

    They'd like to improve on things and correct for refraction.    I don't know of any ready made formulas for correcting for the shift in the position of the horizon due to refraction, since you'd need some model of temperatures etc.     

    I suggested that they could make a 'model' atmosphere that had maybe 4 layers from the surface to the top of the building and then assume either a uniform temperature or a mild uniform gradient and then just do the ray tracing.   I'd imagine this is a bit of pain, but not outside of their capabilities.   

    On a related note, since I talked about this effect, they keep asking me about whether they need to correct their dip angle for refraction and it takes a bit of time and patience to show them the relative size of the two effects for an observer only a few feet above sea level.





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