Abstract

Using a digital camera and linearly polarizing film, we have developed a method for observing neutral point locations in the natural light field of the atmosphere. Utilizing this method, we have observed neutral points in the upwelling light field above a water surface. We report the location of these neutral points and compare them to Monte Carlo simulations.

© 2012 Optical Society of America

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References

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  1. K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, 1988).
  2. G. Horvath and D. Varju, Polarized Light in Animal Vision: Polarization Patterns in Nature (Springer, 2004).
  3. G. V. Rozenberg, Twilight (Plenum, 1966).
  4. J. T. Adams and G. W. Kattawar, “Neutral points in an atmosphere–ocean system. 1: upwelling light field,” Appl. Opt. 36, 1976–1986 (1997).
    [CrossRef]
  5. G. Horváth, B. Bernáth, B. Suhai, A. Barta, and R. Wehner, “First observation of the fourth neutral point polarization point in the atmosphere,” J. Opt. Soc. Am. A 19, 2085–2099 (2002).
    [CrossRef]
  6. K. J. Voss, A. R. Gleason, H. R. Gordon, G. W. Kattawar, and Y. You, “Observation of the non-principal plane neutral points in the in-water upwelling polarized light field,” Opt. Express 19, 5942–5952 (2011).
    [CrossRef]
  7. R. L. Lee, “Digital imaging of clear-sky polarization,” Appl. Opt. 37, 1465–1476 (1998).
    [CrossRef]
  8. J. T. Adams and D. J. Gray, “Neutral points in an atmosphere–ocean system. 2: downwelling light field,” Appl. Opt. 50, 335–346 (2011).
    [CrossRef]
  9. H. C. van de Hulst, Light Scattering by Small Particles (Dover, 1981).

2011 (2)

2002 (1)

1998 (1)

1997 (1)

Adams, J. T.

Barta, A.

Bernáth, B.

Coulson, K. L.

K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, 1988).

Gleason, A. R.

Gordon, H. R.

Gray, D. J.

Horvath, G.

G. Horvath and D. Varju, Polarized Light in Animal Vision: Polarization Patterns in Nature (Springer, 2004).

Horváth, G.

Kattawar, G. W.

Lee, R. L.

Rozenberg, G. V.

G. V. Rozenberg, Twilight (Plenum, 1966).

Suhai, B.

van de Hulst, H. C.

H. C. van de Hulst, Light Scattering by Small Particles (Dover, 1981).

Varju, D.

G. Horvath and D. Varju, Polarized Light in Animal Vision: Polarization Patterns in Nature (Springer, 2004).

Voss, K. J.

Wehner, R.

You, Y.

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Figures (7)

Fig. 1.
Fig. 1.

Diagram showing the setup of camera and linear polarizer used in capturing images. A central line representing a look vector from the camera through the polarizer is shown. The various orientations of the linear polarizer are indicated by arrows and the angle of the axis of the polarizer in each case.

Fig. 2.
Fig. 2.

Data format for the fish-eye lens images. The center of the image is the nadir, and the outer edge is the horizon. The principal plane is defined by the incident sunlight direction and the zenith.

Fig. 3.
Fig. 3.

Four-color method to determine neutral lines and the formation of neutral points. The colors represent regions where Q and U are positive or negative: white (yellow), both Q and U are negative; dark (blue), Q is negative and U is positive; medium (red), Q is positive and U is negative; light (green), both Q and U are positive. Neutral lines, lines where Q=0 or U=0, are the edges of the colored regions. Neutral points form where neutral lines intersect—where both Q and U change sign simultaneously. In this figure and in Fig. 4, neutral points occur where dark (blue) and medium (red) regions intersect or where light (green) and white (yellow) intersect. The solar zenith angle in this case is 65°.

Fig. 4.
Fig. 4.

The color scheme in this figure is the same as in Fig. 3. In this figure, three pairs of symmetric neutral points occur. The solar zenith angle in this case is 85°.

Fig. 5.
Fig. 5.

Photograph of scene at the National Harbor in Maryland with a horizontally oriented polarizer in front of the camera. In the scene the approximate horizon can be seen as the shoreline.

Fig. 6.
Fig. 6.

Observed neutral point appears 46° from nadir in this observation. The Sun is to the left of the observer, and a second neutral point occurs above and to the left of the first neutral point, but its position cannot be precisely determined. The solar zenith angle is about 81°.

Fig. 7.
Fig. 7.

Two neutral points may be seen in this figure. The first occurs at about 49° from nadir, and the second occurs at 64° from nadir. The solar zenith angle is about 85°.

Equations (3)

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I¯=[IQUV].
Plinear=Q2+U2I.
I=I0°+I90°,Q=I0°I90°,U=2I45°I0°I90°.

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