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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: James C. Wyant
  • Vol. 46, Iss. 23 — Aug. 10, 2007
  • pp: 6019–6032

Imaging polarimetry of forest canopies: how the azimuth direction of the sun, occluded by vegetation, can be assessed from the polarization pattern of the sunlit foliage

Ramón Hegedüs, András Barta, Balázs Bernáth, Victor Benno Meyer-Rochow, and Gábor Horváth  »View Author Affiliations


Applied Optics, Vol. 46, Issue 23, pp. 6019-6032 (2007)
http://dx.doi.org/10.1364/AO.46.006019


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Abstract

Radiance, color, and polarization of the light in forests combine to create complex optical patterns. Earlier sporadic polarimetric studies in forests were limited by the narrow fields of view of the polarimeters used in such studies. Since polarization patterns in the entire upper hemisphere of the visual environment of forests could be important for forest-inhabiting animals that make use of linearly polarized light for orientation, we measured 180° field-of-view polarization distributions in Finnish forests. From a hot air balloon we also measured the polarization patterns of Hungarian grasslands lit by the rising sun. We found that the pattern of the angle of polarization α of sunlit grasslands and sunlit tree canopies was qualitatively the same as that of the sky. We show here that contrary to an earlier assumption, the α-pattern characteristic of the sky always remains visible underneath overhead vegetation, independently of the solar elevation and the sky conditions (clear or partly cloudy with visible sun's disc), provided the foliage is sunlit and not only when large patches of the clear sky are visible through the vegetation. Since the mirror symmetry axis of the α-pattern of the sunlit foliage is the solar-antisolar meridian, the azimuth direction of the sun, occluded by vegetation, can be assessed in forests from this polarization pattern. Possible consequences of this robust polarization feature of the optical environment in forests are briefly discussed with regard to polarization-based animal navigation.

© 2007 Optical Society of America

OCIS Codes
(010.1290) Atmospheric and oceanic optics : Atmospheric optics
(110.2960) Imaging systems : Image analysis
(120.5410) Instrumentation, measurement, and metrology : Polarimetry
(280.1310) Remote sensing and sensors : Atmospheric scattering
(330.7310) Vision, color, and visual optics : Vision

ToC Category:
Polarimetry

History
Original Manuscript: March 8, 2007
Manuscript Accepted: April 23, 2007
Published: August 9, 2007

Virtual Issues
Vol. 2, Iss. 9 Virtual Journal for Biomedical Optics

Citation
Ramón Hegedüs, András Barta, Balázs Bernáth, Victor Benno Meyer-Rochow, and Gábor Horváth, "Imaging polarimetry of forest canopies: how the azimuth direction of the sun, occluded by vegetation, can be assessed from the polarization pattern of the sunlit foliage," Appl. Opt. 46, 6019-6032 (2007)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-46-23-6019

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