# SkyPole - A bio-inspired method to locate the north celestial pole

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Institut Matériaux Microélectronique
Nanosciences de Provence

INSTITUT
DES SCIENCES ETIENNE
DU MOUVEMENT JULES
MAREY

Thomas Kronland-Martinet¹,²*, Léo Poughon¹, Marcel Pasquinelli², David Duché², Julien R Serres¹,³, Stéphane Viollet¹

¹ Aix Marseille Univ, CNRS, ISM, Marseille, France

² Aix Marseille Univ, CNRS, IM2NP, Marseille, France

³ Institut Universitaire de France (IUF), Paris, France

*thomas.kronland-martinet@univ-amu.fr

## Polarization vision

## Animal Navigation

* Insects such as *Cataglyphis* desert ants use **skylight polarization to navigate** [1]

* Skylight polarization can be described by its angle and degree of linear polarization (AoLP and DoLP), modeled from **Rayleigh single scattering model** [2]

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## Celestial rotation

* Migratory birds such as homing pigeons use the **celestial rotation** as a reference for calibrating their magnetic compass [3] [4]

* Celestial rotation helps find the **north celestial pole**, giving access to **geographical north bearing and latitude** [5]

* Celestial rotation can be observed **during night or daytime** [6]

## Question

How could the moving skylight polarization pattern be used to locate the north celestial pole?

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## Method

* DoLP has **plane and radial symmetries**

* Due to those symmetries, comparing DoLP at two moments leads to **radial and plane invariance axes**

* North celestial pole (NCP) is always located on the radial invariance axis

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## Results

<figure><img src="image_12.png" /><figcaption>Method implemented on real polarimetric images</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>Measured north celestial pole's coordinates</figcaption></figure>

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## Conclusion

The proposed method is, to our knowledge, the **only method providing global navigation cues based only on sky polarization images.** No ephemeris, time or GPS signal are required, and its simplicity results in **low computational cost and resources.**

## References

[1] Wehner, Harvard University Press, 2020

[4] Able et al., J. of Comp. Phys., 1995

[7] Kronland-Martinet et al., PNAS, 2023

[2] Coulson, A. Deepak Pub., 1988

[5] Smart, Cambridge University Press, 1977

[3] Emlen, NASA Spec. Pub., 1972

[6] Brines, J. Theor. Biol., 1980

## Image References

Desert Ant : © Michael Mangan & Hugh Pastoll.

Homing Pigeon : © Tim Mossholder - Unsplash

Circumpolar Stars : © Benedikt Markus

Skypole : © T. Kronland-Martinet & ESO/B. Tafreshi