Researches On Orientation And Navigation Method Based On The Polarization Vision Of Animals

Bio-inspired polarized skylight navigation is a new autonomous navigation method using one of the natural attributes of the earth,which is based on the principle of polarization vision possessed by animals and the regular distribution pattern of polarized light in the sky.Due to the concealment and robustness,it can be used as a useful supplement to the existing navigation technologies,providing accurate orientation and attitude information for navigation system especially under the situation of weak or no satellite signal,which has important scientific significance and broad application prospect.As a multi-disciplinary and cross-integrated new research,it involves biology,optics,atmospheric science,neuroscience and signal and information processing technology,and how to obtain required reference direction information during navigation process by detecting sky polarization pattern is the core issue that needs to be addressed.Related biological researches showed that,in the first step,corresponding neural signal is generated from the optical integration of polarized skylight by the array of abundant small photoreceptors in the dorsal rim area(DRA)of animals’ compound eyes;then multi-layer structured polarization-sensitive nervous system is used for the neural integration of polarization information;after coding,transmission and decoding processes,the direction information for orientation is expressed by the 16 columnar compass neurons in the protocerebral bridge(PB)area of the brain finally.However,most of the existing biomimetic researches are only concerned with the simulation of polarized light sensing principle for a single photoreceptor in the DRA and the polarization mapping mechanism of three types of POL-neurons in the optic lobe.Aparently,there is a gap between the biological polarized skylight navigation research and the biomimetic polarized skylight navigation research.Focusing on the core issue in the research of biomimetic polarized skylight navigation and inspired by the polarization vision possessed by animals,this thesis will investigate the following four research questions based on the mechanism of optical integration and neural integration by the photoreceptor array in the DRA and the polarization-sensitive nervous system respectively:(1)Aiming at the simulation of signal source,an analytical model for the celestial distribution of polarized light,accounting for position of the sun,polarization neutral points,wavelength and atmospheric turbidity is proposed by bridging the polarization singularity model,skylight intensity distribution theory and the color space frameworks.At the same time,a method based on complex plane representation is used for mapping the model between three dimensional space and two dimensional plane.Compared with other exsiting analytical models,the simulation results of this model are more consistent with the characteristics and laws of the real polarized skylight distribution,and the comparison with the radiation transmission calculation software(Libradtran)shows that this model could accurately describe main features of the sky polarization pattern with a much higher simulation efficiency.(2)Focusing on the problem of angle measurement ambiguity in exsiting bio-inspired polarized skylight navigation sensors,a new signal processing model including three polarized measuring channels and one non-polarized measuring channel is proposed.This model could extend the range of angle measurement from[-π/4,π/4]to[0,2;r]by comparing the responses of four photoelectric conversion channels and considering the dissymmetrical distribution form of degree of polarization for different regions in the sky.In addition,to avoid the error caused by the difference between eletronic components,the four-quadrant photodiode and time division multiplex access mode are used to design the bionic sensor.At last,the performance of the prototype is verified by a set of testing experiments.(3)Focusing on the current situation that no measuring data can support Barta and Horvdth’s theoretical explanation for the "UV-paradox" in biological polarized skylight navigation research,this thesis provides verification experiments on the degree of polarization,the accuracy of E-vector measurement and the standard deviation of angle measurement under the help of bionic POL-sensor,wide-spectral photodiode and band-pass filter.By sorting the favorableness of these tested wavelengths for natural orientation information acquisition,the reason why most animals choosing UV as their polarized skylight source is expounded,and the conclusions deduced from Pomozi’s measurments in visible spectra is extended."UV-paradox" could now be explained reasonably both in theoretical inference and supporting data by measurements.(4)Two different DRA models(DRA-W and DRA-L)are established to simulate animals’optical integration of the natural polarized skylight information based on the DRA features(including distribution pattern of ommatidia,visual fields and characteristics of every single photoreceptor,special mapping schema of the whole DRA)in crickets,locusts,monarch butterflies and fruit flies;two different POL-ANN models(POL-NW and POL-NL)are established to simulate the neural integration of transformed polarization information based on the mechanism and hierarchical structure of triple directional tunning POL-neurons in the optic lobe and the 16 direction representing columnar compass neurons in the protocerebral bridge.By combining these two kinds of models,a new signal processing method is proposed to distill required direction information during navigation process by measuring the distribution characteristics of the sky polarization pattern.The method conforms to the polarization information processing logic in biological perspective and could provide accurate direction measuring results even under special fragmentary sky polarization patterns.At the same time,a full-sky imaging polarimeter based on beam splitting method is designed.Under the help of this device,any specific directional tunning sky polarization pattern could be reconstructed using the simultaneously obtained three pictures.The original inputs of photoreceptors tunning to different polarization directions in the DRA could be obtained,and the pixels within each photoreceptor ’s visual field could be divided using image segmentation method.Put them together,the real-time direction information during navigation process could be calculated by analysing the measured sky polarization patterns.