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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Vol. 33, Iss. 21 — Jul. 20, 1994
  • pp: 4629–4638

Twilight and daytime colors of the clear sky

Raymond L. Lee, Jr.  »View Author Affiliations


Applied Optics, Vol. 33, Issue 21, pp. 4629-4638 (1994)
http://dx.doi.org/10.1364/AO.33.004629


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Abstract

Digital image analysis of the cloudless sky's daytime and twilight chromaticities challenges some existing ideas about sky colors. First, although the observed colors of the clear daytime sky do lie near the blackbody locus, their meridional chromaticity curves may resemble it very little. Second, analyses of twilight colors show that their meridional chromaticity curves vary greatly, with some surprising consequences for their colorimetric gamuts.

© 1994 Optical Society of America

History
Original Manuscript: September 17, 1993
Revised Manuscript: November 18, 1993
Published: July 20, 1994

Citation
Raymond L. Lee, "Twilight and daytime colors of the clear sky," Appl. Opt. 33, 4629-4638 (1994)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-33-21-4629


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References

  1. C. F. Bohren, A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985). [CrossRef]
  2. E. R. Dixon, “Spectral distribution of Australian daylight,” J. Opt. Soc. Am. 68, 437–450 (1978). [CrossRef]
  3. V. D. P. Sastri, S. R. Das, “Typical spectral distributions and color for tropical daylight,” J. Opt. Soc. Am. 58, 391–398 (1968). [CrossRef]
  4. V. D. P. Sastri, S. R. Das, “Spectral distribution and color of north sky at Delhi,” J. Opt. Soc. Am. 56, 829–830 (1966). [CrossRef]
  5. G. T. Winch, M. C. Boshoff, C. J. Kok, A. G. du Toit, “Spectroradiometric and colorimetric characteristics of daylight in the southern hemisphere: Pretoria, South Africa,” J. Opt. Soc. Am. 56, 456–464 (1966). [CrossRef]
  6. D. B. Judd, D. L. MacAdam, G. Wyszecki, “Spectral distribution of typical daylight as a function of correlated color temperature,” J. Opt. Soc. Am. 54, 1031–1040 (1964). [CrossRef]
  7. H. R. Condit, F. Grum, “Spectral energy distribution of daylight,” J. Opt. Soc. Am. 54, 937–944 (1964). [CrossRef]
  8. Y. Nayatani, G. Wyszecki, “Color of daylight from north sky,” J. Opt. Soc. Am. 53, 626–629 (1963). [CrossRef]
  9. Daylight terminology is confusing at best, although some authors have tried to codify it. See, for example, G. Wyszecki, W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, New York, 1982), p. 11.
  10. R. L. Lee, “Colorimetric calibration of a video digitizing system: algorithm and applications,” Col. Res. Appl. 13, 180–186 (1988). [CrossRef]
  11. We used a Photo Research PR-704 spectroradiometer with a nominal 0.5° FOV.
  12. F. F. Hall, “Twilight sky colors: observations and the status of modeling,” J. Opt. Soc. Am. 69, 1179–1180, 1197 (1979). [CrossRef]
  13. C. N. Adams, G. N. Plass, G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974). [CrossRef]
  14. R. L. Lee, “What are ‘all the colors of the rainbow’?” Appl. Opt. 30, 3401–3407, 3545 (1991). The 1991 printing of Eq. (1) inadvertently omitted the overbars; the reported ĝ values are correct, however. [CrossRef] [PubMed]
  15. R. L. Lee, “Horizon brightness revisited: measurements and a model of clear-sky radiances,” Appl. Opt. 33, 4620–4628 (1994). [CrossRef] [PubMed]
  16. These achromatic stimuli are derived from the extraterrestrial solar irradiances reported by M. P. Thekaekara, “Solar energy outside the earth's atmosphere,” Sol. Energy 14, 109–127 (1973). [CrossRef]
  17. “Relative azimuth” here means azimuth measured with respect to the Sun's azimuth; a relative azimuth of 0° points toward the Sun's azimuth. For the hemispheric daylight chromaticities shown in Figs. 1 and 3, 0° relative azimuth was defined by tilting the surface normal of the radiometer's cosine detector at an angle of 75° from the zenith and by pointing this surface normal toward the Sun's azimuth.
  18. G. J. Burton, I. R. Moorhead, “Color and spatial structure in natural scenes,” Appl. Opt. 26, 157–170 (1987). [CrossRef] [PubMed]
  19. C. J. Bartleson, “Memory colors of familiar objects,” J. Opt. Soc. Am. 50, 73–77 (1960). [CrossRef] [PubMed]
  20. Readers unfamiliar with three-dimensional color spaces and color solids may consult Secs. 3.3.9–3.7 of Ref. 9.
  21. We have not shown a stereogram for the University Park, Pa., chromaticities (Ref. 15, Plate 37) because their noisiness and broad luminance maximum make stereo interpretation difficult.
  22. A. Meinel, M. Meinel, Sunsets, Twilights, and Evening Skies, (Cambridge U. Press, Cambridge, 1983), pp. 51–61. Reference 23 offers a more comprehensive survey of twilight optics.
  23. G. V. Rozenberg, Twilight: A Study in Atmospheric Optics (Plenum, New York, 1966).
  24. M. G. J. Minnaert, Light and Color in the Outdoors, translated and revised by L. Seymour, (Springer-Verlag, New York, 1993), pp. 295–297.
  25. Strictly speaking, the twilight arch is defined only for solar depression angles of ∼7°–16°. See, for example, H. Neuberger, Introduction to Physical Meteorology (Penn State Press, University Park, Pa., 1957), p. 185. However, the yellow band in Plate 43 (solar depression ∼2°) is a local luminance maximum, and it remained so for solar depression angles >7°.
  26. T. Deshler, B. J. Johnson, W. R. Rozier, “Balloonborne measurements of Pinatubo aerosol during 1991 and 1992 at 41° N: vertical profiles, size distribution, and volatility,” Geophys. Res. Lett. 20, 1435–1438 (1993). [CrossRef]
  27. Although the twilight seen in Hall's Plate 116 (dated 17 August 1978; see Ref. 12) may be the basis for his Fig. 1, Hall does not state this unambiguously, thus making the issue of stratospheric aerosol loading moot for his data. In any case, the pastel colors of Hall's Plate 116 are quite different from those of vivid posteruption twilights (e.g., our Plate 43).

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