Design of a device for sky light polarization measurements.

Yujie Wang,Tao Ma,Lilian Zhang,Junxiang Lian,Xiaoping Hu,Zhiwen Xian

doi:10.3390/s140814916

Abstract

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky.

Highlights

Since the discovery of sky light polarization by the French natural philosopher Arago in 1809, it has been studied for many reasons
This paper has presented the design of a device for sky light polarization measurements and the preliminary experiments related to its evaluation
Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are proposed

Summary

Introduction

Since the discovery of sky light polarization by the French natural philosopher Arago in 1809, it has been studied for many reasons. Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a compass for navigation. The understanding of these optical characteristics has been one of the most interesting and important problems in atmospheric optics [1,2,3,4]. The polarization pattern of the sky conveys rich information about the orientation of the sun [5]. It is becoming apparent that most animal groups are capable of detecting and using this type of light for a number of different tasks [4,6,7,8]

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