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    From: George Huxtable
    Date: 2005 Aug 27, 13:25 +0100

    Catherine Hohenkerk, the personification of HM Nautical Almanac Office, has
    just kindly sent me a paper, NAO technical note No 63, by C Y Hohenkerk and
    A T Sinclair,  dated April 1985, "The computation of Atmospheric Refraction
    al large Zenith Angles", which appears to cover the subject rather thoroughly.
    It splits the integration into two zones; the troposphere (up to 11 km),
    with a constant, but adjustable lapse rate, and the stratosphere, with a
    lapse rate of zero. It shows good agreement with Garfinkel, for zenith
    angles 75 to 90 degrees (altitudes 25 to 0) and with Saastamoinen from 10
    to 80 degrees (altitudes 80 to 10), if the same lapse rates as theirs are
    chosen. Lapse rate is the  assumed drop in temperature with increasing
    height, for which a value of .0065 degrees per metre is suggected. Fortran
    programs are included.
    It refers to a "simple description" of refraction, contained in another NAO
    note, No 59, by Sinclair (1982), which she has also sent; "The effect of
    atmospheric refraction on laser ranging data". (That infomation may
    possibly be useful in correcting GPS signals for atmospheric transit delays.)
    It also refers to a Yale University atmospheric department note on
    "Astronomical Refraction", by L H Auer and E M Standish, of 1979, and
    handwritten in is a much later reference to Auer and Standish, in the
    Astronomical Journal 119, pages 2472 to 2474, May 2000. This is entitled
    "Astronomical Refraction: Computational methods for all zenith angles".
    I won't attempt to summarise the Hohenkerk Sinclair technical note; it
    might well be beyond me if I tried. It may appeal to the more
    mathematically-inclined list members. If anyone asks, I will scan it as an
    attachment for individuals; 13 pages. But I suspect that Catherine would be
    happy to post copies, if you asked her nicely, at HM Nautical Almanac
    Office, Space Science and Technology Dewpartment, Rutherford Appleton
    Laboratory, Chilton, Didcot OX11 0QX, England,  e-mail hmnao@nao.rl.ac.uk
    Contact George at george@huxtable.u-net.com ,or by phone +44 1865 820222,
    or from within UK 01865 820222.
    Or by post- George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13
    5HX, UK.

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