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Re: Astronomical Refraction: Computational Method for All Zenith Angles
From: Marcel Tschudin
Date: 2005 Aug 23, 01:52 +0300
From: Marcel Tschudin
Date: 2005 Aug 23, 01:52 +0300
Frank, you wrote > Today, I coded up a much better way of dealing with all of this > atmospheric > structure. I generate a density table directly from the temperature > profile > of the atmosphere (this is the principal independent variable) and the > condition of hydrostatic equilibrium and the ideal gas law which is how > atmosphere > models are derived usually. While these equations can be integrated > analytically in important special cases you then have to do a lot of work > patching > together the pieces. But if you do the integration numerically from the > ground > up, it's trivial to modify the temperature profile, generate new > atmosphere > data, and then re-run the refraction tables. Added what you proposed. Density values look resonable, BUT ... > And that's it. This model can then be used as input to the refraction > integration. Using a lapse rate of 5.70 deg C per kilometer below 11km > altitude and > a rate of zero above that altitude, I was able to replicate almost > exactly > the refraction tables in the Auer-Standish article. The differences were > mostly less than one-tenth of a second of arc. I would have wished to get such results, mine are substancially higher... I checked and checked and can still not findout why. Further you wrote > By the way, Marcel, thanks for raising this issue. It's led me to all > sorts > of interesting things. ...and I did not imagine that I finally would spend so much time on it. Your "interesting things" gave me courage and the input to start writing a program for it. At the moment, it looks as I am stuck half way. Marcel