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    Re: Refraction
    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?

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