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    Re: Refraction
    From: Marcel Tschudin
    Date: 2005 Aug 26, 19:41 +0300

    George wrote
    > I'm pleased that Marcel has followed up my lead to Andrew Young's useful
    > series, and that Andy has come up with the goods, as I expected he would.
    
    Yes, I followed your suggestion, and indeed Andy Young was very helpful in
    discussing the subject via mail.
    
    George asks further
    > Presumably, Sunset science 4 has references to the previous 3 instalments.
    > Is it the concluding item in that series, or are there others to follow?
    > It
    > would be helpful if Marcel would list references to all the items in this
    > series for which he has details. No doubt, several listmembers would find
    > them interesting.
    
    The three preceiding papers are indeed mentioned. To make it easier for all
    those who are interested, I just add the references from NASA ADS by
    copy/paste at the end of this mail. The abstract can be read at ADS.
    Unfortunately all these articles can not be downloaded for free. I was not
    able to find out whether the series will continue or not.
    
    Let me just mention the last part of his conclusions:
    
    "Refraction within about 5deg of the horizon is so variable that no a priori
    formula or table can be expected to give accurate values there; the local
    lapse rate and thickness of the boundary layer above the observer must be
    known. However, numerical integration using standard lapse rate, matched to
    the actual temperature and pressure at the observer, should give values good
    to a minute of arc or so - that is, good enough for telescope pointing -
    down to 2deg or 3deg apparent altitude.
    Below that, numerical integrations will give useful values if the actual
    boundary-layer lapse rate and thickness are known, but only the bottom
    kilometer or so of the atmosphere needs to be measured, and ordinary balloon
    soundings are adequate. At and below the astronomical horizon, the
    refraction depends primarily on atmospheric structure below the observer and
    varies so much (tens of minutes, or even several degees) that only very
    crude predictions can be made. The observed time of sunset at a sea horizon
    often varies by a few minutes from day to day, and the variations increase
    with height above the sea."
    
    That is more or less what also Frank found after having calculated various
    models using the BAS pocedure, as Andy Young calls it. I hope that Frank's
    transfer function for calculating refraction as a function of altitude and
    height receives the appreciation it deserves.
    
    Marcel
    
    Here now the references:
    
          Title:
         Sunset science. I. The mock mirage
          Authors:
         Young, Andrew T.; Kattawar, George W.; Parviainen, Pekka
          Journal:
         Applied Optics LP, vol. 36, Issue 12, pp.2689-2700
          Publication Date:
         04/1997
          Origin:
         AIP; OSA
          Bibliographic Code:
         1997ApOpt..36.2689Y
    
    
          Title:
         Sunset Science. II. A useful diagram
          Authors:
         Young, Andrew T.; Kattawar, George W.
          Journal:
         Applied Optics LP, vol. 37, Issue 18, pp.3785-3792
          Publication Date:
         06/1998
          Origin:
         AIP; OSA
          Bibliographic Code:
         1998ApOpt..37.3785Y
    
    
    
          Title:
         Sunset science. III. Visual adaptation and green flashes
          Authors:
         Young, Andrew T.
          Journal:
         Journal of the Optical Society of America A: Optics, Image Science, and
    Vision, Volume 17, Issue 12, December 2000, pp.2129-2139
          Publication Date:
         12/2000
          Origin:
         AIP; OSA
          Bibliographic Code:
         2000OSAJ...17.2129Y
    
    
          Title:
         Sunset Science. IV. Low-Altitude Refraction
          Authors:
         Young, Andrew T.
          Affiliation:
         AA(Department of Astronomy, San Diego State University, 5500 Campanile
    Drive, San Diego, CA 92182-1221 aty{at}mintaka.sdsu.edu)
          Journal:
         The Astronomical Journal, Volume 127, Issue 6, pp. 3622-3637. (AJ
    Homepage)
          Publication Date:
         06/2004
          Origin:
         UCP
          AJ Keywords:
         Atmospheric Effects
          Abstract Copyright:
         (c) 2004: The American Astronomical Society
          DOI:
         10.1086/420806
          Bibliographic Code:
         2004AJ....127.3622Y
    
    
    

       
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