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Applied Optics

Applied Optics


  • Vol. 39, Iss. 21 — Jul. 20, 2000
  • pp: 3612–3619

Skerrylike mirages and the discovery of Greenland

Waldemar H. Lehn  »View Author Affiliations

Applied Optics, Vol. 39, Issue 21, pp. 3612-3619 (2000)

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The Norse discovery of Greenland is associated with the sighting of low barren islands called Gunnbjörn’s Skerries, which have never been satisfactorily identified. Here the historical references that connect the skerries to Greenland are reviewed. A mirage of the Greenland coast, arising specifically from optical ducting under a sharp temperature inversion, is used to explain the vision of skerries seen by the Norse mariners. Images from both ducting and uniform inversions are calculated. Under the assumption of a clean Rayleigh atmosphere, sufficient visibility remains to see the skerry image at a distance of 220 km. There is significant circumstantial evidence to indicate that the Norse were familiar with the skerrylike mirage and that they used it to discover new lands.

© 2000 Optical Society of America

OCIS Codes
(000.2850) General : History and philosophy
(010.0010) Atmospheric and oceanic optics : Atmospheric and oceanic optics
(010.4030) Atmospheric and oceanic optics : Mirages and refraction

Original Manuscript: October 21, 1999
Revised Manuscript: May 8, 2000
Published: July 20, 2000

Waldemar H. Lehn, "Skerrylike mirages and the discovery of Greenland," Appl. Opt. 39, 3612-3619 (2000)

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  1. G. Jones, The Norse Atlantic Saga (Oxford, London, 1964).
  2. K. Gjerset, History of Iceland (MacMillan, New York, 1924).
  3. F. Nansen, In Northern Mists, 2 Vols. (Heinemann, London, 1911; reprinted by AMS New York, 1969).
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  6. In Ref. 3, Vol. 1, p. 263, Nansen quotes Björn Jónsson’s Grönlands Annaler (1625) from Grønlands historiske Mindesmærker (The Historical Records of Greenland) (Copenhagen 1838 ff), Vol. 1, p. 88.
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  8. Ref. 1; p. 129.
  9. Ref. 1; 165.
  10. The Blosseville Coast consists of very high mountains (the Watkins Range), the highest of which, Gunnbjörns Fjæld, exceeds 3900 m.
  11. All geographical information is taken from the global digital elevation model GTOPO30. This public-domain digital elevation model, which covers the globe at a resolution of 30 arc sec, is obtainable at http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html . The map and the perspective images of Fig. 2 are produced with Generic Mapping Tools Version 3.2 (available from http://www.soest.hawaii.edu/gmt ). See also P. Wessel, W. H. F. Smith, “New, improved version of the Generic Mapping Tools released,” Eos Trans. Am. Geophys. Union 79, 579 (1998).
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  15. Mt. Rigny, a mountain of elevation 2470 m, is located 35 km inland from the Greenland coast, nearly along the shortest line of sight from Iceland to Greenland. Its distance from Snæfjall (793 m) in Iceland is 357 km. In the standard atmosphere the horizon distance d (km) from either peak is approximately d = 3.9 h, where h is the elevation in meters. For an observer whose eye elevation is 3 m, a ray tangent to the horizon would meet the tips of Snæfjall and Mt. Rigny at distances 117 km and 201 km, respectively. The gap in intervisibility is thus 39 km. However, the distance to be sailed without a comfortable view of land (say, 5 arc min high) is somewhat longer, 62 km.
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  17. Ref. 3, Vol. 1, p. 262; the account of Ivar Bardsson.
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  22. John Ross, A Voyage of Discovery (Murray, London, 1819).
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  30. T. Búason, “Mirages and vertical contraction of images of distant objects,” P.O. Box 273, 101 Reykjavik, Iceland (personal communication, 1998).
  31. W. H. Lehn, T. L. Legal, “Long-range superior mirages,” Appl. Opt. 37, 1489–1494 (1998). [CrossRef]
  32. G. Wyszecki, W. S. Stiles, Color Science, 2nd ed. (Wiley, New York, 1982), p. 569.
  33. W. G. Driscoll, W. Vaughan, eds., Handbook of Optics (McGraw-Hill, New York, 1978).
  34. G. L. Trusty, T. H. Cosden, “Optical extinction predictions from measurements aboard a British weather ship,” J. Opt. Soc. Am. 70, 1561 (1980). Aerosol extinctions as low as 0.002 km-1 were recorded for light of wavelength 550 nm.
  35. F. Baur, Meteorologisches Taschenbuch (Akademische Verlagsgesellschaft, Leipzig, 1970), Vol. 2, p. 525.
  36. M. Born, E. Wolf, Principles of Optics, 6th ed. (Pergamon, Oxford, 1986), p. 95.
  37. W. E. K. Middleton, “Vision through the Atmosphere,” Handbuch der Physik (Springer, Berlin, 1957), Vol. 48, pp. 254–287. The distance at which the transmission factor equals 0.02 (the minimum contrast detectable by the human eye) gives Koschmieder’s visual range for a black object.

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