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Re: Refraction
From: Marcel Tschudin
Date: 2005 Aug 27, 17:04 +0300
From: Marcel Tschudin
Date: 2005 Aug 27, 17:04 +0300
> Marcel, you wrote: > "Does the Nautical Almanac have a different table than the previously > mentioned table 6 from Pub. No. 249? If so, which title, page number > etc.? > Or, is there an other possibility to obtain it, instead of ordering it > from > "my" library abroad?" > > It's distinct from the table in pub. 249. The latter tables are intended > for > aviators so they include calculations for higher observer altitudes and > they > are rather low accuracy. The refraction tables in the Nautical Almanac > are > precise to the nearest tenth of a minute of arc and extend right down to > the > horizon in small steps. They are limited to observations made close to > sea > level. Do you want copies? If it isn't to difficult, yes please. Thank you. > You asked: > "Wouldn't it be possible to find the authors of the table and ask them > which > model they used und why? Or, are there some clarifying comments in the > Almanac?" > > There is no clarification in the almanac. The refraction tables published > there were fixed and unchanging for fifty years. They were modified very > slighly just a couple of years ago. Myself, I'm not too worried about how > they > calculated either the original table or the new version since we can > calculate > almost exact matches using simple atmospheric models. And that's good > enough, > as far as I'm concerned. We seem to have different goals. You were apparently happy to find the parameters to reproduce the data shown (I also would have been happy on this). I just was questioning the reason why they used a lapse rate - if I understood you correct - of 7.25 deg C up to 11km height. Of all the temperature profiles I found so far, the average lapse rate within the troposphere, i.e. below the 11km height, was smaller than this value. It is for this reason that it would be interesting to know the reason for their model. Does the Nautical Almanac provide contact addresses? Marcel