Study On Polarization Properties Of Skylight And Test Instrument

Creatures like Cataglyphis and Crickets could use skylight polarization for navigation through their small compound eyes and brain, hereby accomplishing to go out foraging and return to nests. Enlightened by these facts, bionic polarization navigation was gradually attached much more importance by people. Owning to several advantages of bionic polarization navigation technology, such as stability, high accuracy and interference-free, it was already the research highlight in navigation field. As the carrier of bionic polarization navigation, skylight polarization distribution pattern became the key to conquer the bionic optical navigation technology. Hence, in this paper, the imaging skylight polarization test instrument was designed and the law of skylight polarization was studied.We profoundly started from analyzing atmosphere components, and then studied the fundamental characteristics of Rayleigh scattering and Mie scattering. The formation mechanism of skylight polarization distribution pattern was clarified, and celestial sphere and horizon coordinate line was brought in. Besides, on the basis of Rayleigh scattering theory, the skylight polarization model was established. Through simulation analysis on sunlight and moonlight polarization distribution pattern, its law was naturally obtained.Applied to long-term automatic test, a set of imaging skylight polarization test measurement system was designed, and then linearity and multiplicity calibration was completed. The influence of linear polarizer and the fish-eye lens optical system on incident light polarization was evaluated and replenished. On this account, the testing accuracy of testing instrument met the requirements.A complete data storage and analysis software system was designed to be capable of conducting data storage and real-time data reading. With Rayleigh scattering model embedded in, it was convenient to compare and analyze test results with the help of theoretical models. All kinds of information, such as testing time, location, weather condition, aerosol thickness and visibility, were altogether stored in the database to carry out tracking test and analysis of skylight polarization easily. As the sunlight polarization distribution pattern was tested continuously via testing instruments, dynamic characteristics of sunlight polarization distribution pattern and difference between the actual test and the theoretical distribution pattern were gained. By means of analyzing cloudy and sunny twilight polarization distribution pattern, the influence of polarization distribution regularities under two kinds of different weather conditions and cloud upon polarization property was figured out.The research showed this:Polarization distribution patterns varied with the changing position of sun. The distribution of polarization degree was distributed symmetrically around the neutral point. The distribution of polarization angle was distributed symmetrically around maximum polarization line and meridian, which shaped like’∞’. The entire polarization distribution pattern rotated around the celestial pole point. The average degree of polarization increased at first and then decreased, increased and then increased again with time. The average value of red wave-band polarization was maximum, followed by green wave-band and blue wave-band was minimal. The polarization distribution pattern in sunny days was same as cloudy days. In cloudy days, the lower polarization degree area occupied a large proportion. In sunny days, the polarization distribution pattern was nearly same as Rayleigh scattering model. As sun and nearby sun spots damaged polarization distribution pattern around the sun, we should avoid this area when using skylight polarization for navigation and testing.