# Comparison between skylight polarization in visible and ultraviolet spectra for heading measurements

Antoine Moutenet, Julien Serres, Stéphane Viollet

► To cite this version:

Antoine Moutenet, Julien Serres, Stéphane Viollet. Comparison between skylight polarization in visible and ultraviolet spectra for heading measurements. Journée des Jeunes Chercheurs en Robotique (JJCR 2023), GDR Robotique; Franck Ruffier; Maan El Badaoui El Najjar, Oct 2023, Moliets et Maâ, France. hal-04519955

HAL Id: hal-04519955

https://hal.science/hal-04519955

Submitted on 25 Mar 2024

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Comparison between skylight polarization in visible and ultraviolet spectra for heading measurements

Antoine Moutenet, Julien Serres, Stéphane Viollet

► To cite this version:

Antoine Moutenet, Julien Serres, Stéphane Viollet. Comparison between skylight polarization in visible and ultraviolet spectra for heading measurements. Journée des Jeunes Chercheurs en Robotique (JJCR 2023), GDR Robotique; Franck Ruffier; Maan El Badaoui El Najjar, Oct 2023, Moliets et Maâ, France. hal-04519955

HAL Id: hal-04519955

https://hal.science/hal-04519955v1

Submitted on 25 Mar 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Comparison between skylight polarization
in visible and ultraviolet spectra for
heading measurements

Antoine Moutenet<fnref n="1" />,<fnref n="2" />, Julien R. Serres<fnref n="2" />,<fnref n="3" />, Stéphane Viollet<fnref n="2" />

**Keywords:** Ultraviolet (UV), skylight polarization, Rayleigh scattering, celestial compass, polarized vision.

In the field of autonomous outdoor navigation, the calculation of a precise heading is essential. For more than one century, numerous studies have been carried out on the ability of navigating insects, such as desert ants *Cataglyphis fortis* [1], to find their bearings thanks to the polarization of light scattered by the atmosphere [2] (Fig. 1, left). In space, the sunlight is naturally unpolarized, however, it is scattered by atmospheric molecules, and then becomes polarized according to a very precise pattern seen from the ground. This make it possible to find the sun’s position, even if the sun is hidden [3]. Although it has already been possible to build celestial compasses based on this polarization phenomenon, it tends to be corrupted in the visible spectrum on overcast days, limiting their use [4]-[11].

<figure><img src="image_2.png" /><figcaption>Figure 1: From left to right: The visual field distributions of a desert ant to navigation. Two cameras used for our measurements, one working in the visible range (a) and another one in the UV range (b). Examples of polarization angle patterns (*AoP*<sub>l</sub>) measured. 1 & 2 correspond to clear and overcast skies, respectively. Visible and UV measurements are marked V and UV, respectively, angles in degrees correspond to different camera orientations.</figcaption></figure>

<footnote n="1">¹Safran Electronics&Defense, Massy, France</footnote>

<footnote n="2">²Aix Marseille Univ, CNRS, ISM, Marseille, France</footnote>

<footnote n="3">³Institut Universitaire de France (IUF), Paris, France</footnote>
Comparison between skylight polarization
in visible and ultraviolet spectra for
heading measurements

Antoine Moutenet<fnref n="1" />,<fnref n="2" />, Julien R. Serres<fnref n="2" />,<fnref n="3" />, Stéphane Viollet<fnref n="2" />

**Keywords:** Ultraviolet (UV), skylight polarization, Rayleigh scattering, celestial compass, polarized vision.

In the field of autonomous outdoor navigation, the calculation of a precise heading is essential. For more than one century, numerous studies have been carried out on the ability of navigating insects, such as desert ants *Cataglyphis fortis* [1], to find their bearings thanks to the polarization of light scattered by the atmosphere [2] (Fig. 1, left). In space, the sunlight is naturally unpolarized, however, it is scattered by atmospheric molecules, and then becomes polarized according to a very precise pattern seen from the ground. This make it possible to find the sun’s position, even if the sun is hidden [3]. Although it has already been possible to build celestial compasses based on this polarization phenomenon, it tends to be corrupted in the visible spectrum on overcast days, limiting their use [4]-[11].

<figure><img src="image_2.png" /><figcaption>Figure 1: From left to right: The visual field distributions of a desert ant to navigation. Two cameras used for our measurements, one working in the visible range (a) and another one in the UV range (b). Examples of polarization angle patterns (*AoP*<sub>l</sub>) measured. 1 & 2 correspond to clear and overcast skies, respectively. Visible and UV measurements are marked V and UV, respectively, angles in degrees correspond to different camera orientations.</figcaption></figure>

<footnote n="1">¹Safran Electronics&Defense, Massy, France</footnote>

<footnote n="2">²Aix Marseille Univ, CNRS, ISM, Marseille, France</footnote>

<footnote n="3">³Institut Universitaire de France (IUF), Paris, France</footnote>
However, still relying on insects which initially inspired us, we can see that they
are sensitive not only to visible light polarization, but also to ultraviolet polarization
[1], which could be the key to navigating under overcast skies using polarimetry [4]-[8].
We therefore decided to setup a UV polarimetric camera (UV-sensitive camera with a
rotating UV linear polarizer and an objective directly mounted onto it, composed of
a UV-centered band-passfilter and a pinhole of 50µm or 200µm), because it was not
commercially available, and to compare its levels of performance with a conventional
visible polarimetric camera (polarized monochromatic camera), under different weather
conditions (Fig. 1, right).

Our preliminary results with our UV-sensitive camera in overcast conditions are not
yet as good as those we get from our visible camera in clear conditions, notably because
of the very long integration time intrinsic to the UV-sensitive sensor's rusticity. Despite
mixed results, this study does demonstrate the advantage we can get by looking into
this new type of sensors.

References

[1] R. Wehner. *Desert navigator: the journey of an ant*. Harvard University Press, 2020.

[2] F. Kong, Y. Guo, J. Zhang, X. Fan, X. Guo. *Review on bio-inspired polarized skylight navigation*. Chinese Journal of Aeronautics. Vol. 36, No. 9, pp. 14-37, 2023.

[3] G. Horváth and D. Varjú. *Polarized Light in Animal Vision*, 2004.

[4] X. Wang, J. Gao and Z. Fan. *Empirical corroboration of an earlier theoretical resolution to the UV paradox of insect polarized skylight orientation*. Naturwissenschaften, Vol. 101, pp. 95-103, 2014.

[5] I. Pomozi, G. Horváth, and R. Wehner. *How the clear-sky angle of polarization pattern continues underneath clouds: full-sky measurements and implications for animal orientation*. J. of Experimental Biology, Vol. 204, No 17, pp. 2933-2942, 2001.

[6] M. Blumthaler and M. Schwarzmann. *Spectral measurements of the polarization of UV sky radiance*. Ultraviolet ground-and space-based measurements, models, and effects V (Vol. 5886, pp. 18-25). SPIE. 2005.

[7] N. Carey, and W. Sturzl. *An insect-inspired omnidirectional vision system including UV-sensitivity and polarisation*. 2011 IEEE International Conference on Computer Vision Workshops (ICCV Workshops) (pp. 312-319). IEEE, 2011.

[8] H. Zhao, W. Xu. *A Bionic Polarization Navigation Sensor and Its Calibration Method*. Sensors, Vol. 16, No. 8, p. 1223, 2016.

[9] M. V. Berry, M. R. Dennis, and R. L. Jr Lee. *Polarization singularities in the clear sky*. New Journal of Physics, Vol. 6, No. 1, p. 162, 2004.

[10] G. Horvath, B. Bernath, B. Suhai, and A. Barta. *First observation of the fourth neutral polarization point in the atmosphere*. JOSA, Vol. 19, No 10, pp. 2085-2099, 2002.

[11] H. Lu 1, Y. Xie, K. Zhang, H. Zhang, X. M. Zou, J. Wang, and K. C. Zhao. *Construction and test of bio-inspired imaging polarization navigation prototype*. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 43, pp. 323-329, 2020.
However, still relying on insects which initially inspired us, we can see that they
are sensitive not only to visible light polarization, but also to ultraviolet polarization
[1], which could be the key to navigating under overcast skies using polarimetry [4]-[8].
We therefore decided to setup a UV polarimetric camera (UV-sensitive camera with a
rotating UV linear polarizer and an objective directly mounted onto it, composed of
a UV-centered band-passfilter and a pinhole of 50µm or 200µm), because it was not
commercially available, and to compare its levels of performance with a conventional
visible polarimetric camera (polarized monochromatic camera), under different weather
conditions (Fig. 1, right).

Our preliminary results with our UV-sensitive camera in overcast conditions are not
yet as good as those we get from our visible camera in clear conditions, notably because
of the very long integration time intrinsic to the UV-sensitive sensor's rusticity. Despite
mixed results, this study does demonstrates the advantage we can get by looking into
this new type of sensors.

References

[1] R. Wehner. *Desert navigator: the journey of an ant*. Harvard University Press, 2020.

[2] F. Kong, Y. Guo, J. Zhang, X. Fan, X. Guo. *Review on bio-inspired polarized skylight navigation*. Chinese Journal of Aeronautics. Vol. 36, No. 9, pp. 14-37, 2023.

[3] G. Horváth and D. Varjú. *Polarized Light in Animal Vision*, 2004.

[4] X. Wang, J. Gao and Z. Fan. *Empirical corroboration of an earlier theoretical resolution to the UV paradox of insect polarized skylight orientation*. Naturwissenschaften, Vol. 101, pp. 95-103, 2014.

[5] I. Pomozi, G. Horváth, and R. Wehner. *How the clear-sky angle of polarization pattern continues underneath clouds: full-sky measurements and implications for animal orientation*. J. of Experimental Biology, Vol. 204, No 17, pp. 2933-2942, 2001.

[6] M. Blumthaler and M. Schwarzmann. *Spectral measurements of the polarization of UV sky radiance*. Ultraviolet ground-and space-based measurements, models, and effects V (Vol. 5886, pp. 18-25). SPIE. 2005.

[7] N. Carey, and W. Sturzl. *An insect-inspired omnidirectional vision system including UV-sensitivity and polarisation*. 2011 IEEE International Conference on Computer Vision Workshops (ICCV Workshops) (pp. 312-319). IEEE, 2011.

[8] H. Zhao, W. Xu. *A Bionic Polarization Navigation Sensor and Its Calibration Method*. Sensors, Vol. 16, No. 8, p. 1223, 2016.

[9] M. V. Berry, M. R. Dennis, and R. L. Jr Lee. *Polarization singularities in the clear sky*. New Journal of Physics, Vol. 6, No. 1, p. 162, 2004.

[10] G. Horvath, B. Bernath, B. Suhai, and A. Barta. *First observation of the fourth neutral polarization point in the atmosphere*. JOSA, Vol. 19, No 10, pp. 2085-2099, 2002.

[11] H. Lu 1, Y. Xie, K. Zhang, H. Zhang, X. M. Zou, J. Wang, and K. C. Zhao. *Construction and test of bio-inspired imaging polarization navigation prototype*. The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. 43, pp. 323-329, 2020.