Polarization Characteristics of Forest Canopies with Biological Implications

Chapter
Part of the Springer Series in Vision Research book series (SSVR, volume 2)

Abstract

In this chapter we show that the pattern of the direction of polarization of sunlit grasslands and sunlit tree canopies is qualitatively the same as that of the clear sky. Since the mirror symmetry axis of this pattern is the solar–antisolar meridian, the azimuth direction of the sun, occluded by vegetation, can be assessed in forests from this polarization pattern. This robust polarization feature of the optical environment in forests can be important for forest-inhabiting animals that make use of linearly polarized light for orientation. Here we also present an atmospheric optical and receptor-physiological explanation of why longer wavelengths are advantageous for the perception of polarization of downwelling light under canopies illuminated by the setting sun. This explains why the upward-pointing ommatidia of the dusk-active cockchafers, Melolontha melolontha, detect the polarization of downwelling light in the green part of the spectrum. We show that the polarization vision in Melolontha melolontha is tuned to the high polarized intensity of downwelling light under canopies during sunset. This is an optimal compromise between simultaneous maximization of the quantum catch and the quantum catch difference.

Supplementary material

71484_2_En_17_MOESM1_ESM.zip (2.4 mb)
Supplementary Fig. 17.1Colour photograph, and patterns of the degree of linear polarization d and the angle of polarization α from the local meridian of a grassland lit by the rising sun. The measurements were performed from a hot air balloon at an altitude of 100 m. The optical axis of the fish-eye lens pointed towards the nadir, which is the centre of the circular patterns [after Fig. 2 on page 6025 of Hegedüs et al. (2007a, b, c, d)] (CDR 2461 kb)
71484_2_En_17_MOESM2_ESM.zip (3 mb)
Supplementary Fig. 17.2Colour photograph, and patterns of the degree of linear polarization d and the angle of polarization α from the local meridian of a clear sky with the overhead vegetation of a forest composed of birch trees lit by the setting sun measured by full-sky imaging polarimetry in the red, green and blue parts of the spectrum. In pattern bblack shows the tree foliage and white indicates the sky [after Fig. 3 on page 6026 of Hegedüs et al. (2007a, b, c, d)] (CDR 3120 kb)
71484_2_En_17_MOESM3_ESM.zip (1.7 mb)
Supplementary Fig. 17.3Colour photograph (a), and patterns of the degree of linear polarization d and the angle of polarization α from the local meridian of a clear sky, measured by full-sky imaging polarimetry in the red, green and blue parts of the spectrum. The optical axis of the fish-eye lens was vertical, thus the horizon is the perimeter and the centre of the circular patterns is the zenith. At the perimeter of the circular colour picture the dark silhouette of trees can be seen. The sun near the horizon was occluded by a small black disc placed on a thin wire, which is seen radially in the circular patterns [after Fig. 1 on page 6023 of Hegedüs et al. (2007a, b, c, d)] (CDR 1764 kb)
71484_2_En_17_MOESM4_ESM.zip (16.3 mb)
Supplementary Fig. 17.4Colour photographs and α-patterns of skies and tree canopies measured in the blue (450 nm) part of the spectrum. Quite similar α-patterns were obtained in the green and red spectral ranges [after Fig. 4 on page 6027 of Hegedüs et al. (2007a, b, c, d)] (CDR 16728 kb)
71484_2_En_17_MOESM5_ESM.zip (3.8 mb)
Supplementary Fig. 17.5Colour photograph, and patterns of the degree of linear polarization d and the angle of polarization α (clockwise from the local meridian) of a grassland lit by the rising sun. The measurements were performed from a hot air balloon at an altitude of 150 m. The optical axis of the fish-eye lens pointed towards the nadir, which is the centre of the circular patterns (CDR 3761 kb)
71484_2_En_17_MOESM6_ESM.zip (3.7 mb)
Supplementary Fig. 17.6As Supplementary Fig. 17.5 for a grassland lit by the rising sun and measured from a hot air balloon at an altitude of 200 m (CDR 3855 kb)

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Environmental Optics Laboratory, Department of Biological Physics, Physical InstituteEötvös UniversityBudapestHungary
  2. 2.Max Planck Institute for InformaticsSaarbrueckenGermany
  3. 3.INRIA Sud-Ouest BordeauxTalenceFrance
  4. 4.Laboratoire Photonique, Numérique et Nanosciences (L2PN), UMR 5298CNRS IOGS University Bordeaux, Institut d’Optique d’AquitaineTalenceFrance

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