Polarization Navigation Sensor Research Articles

Design of a real-time orientation sensor based on atmospheric polarization light.

In recent years, biomimetic polarization navigation has become a research hotspot in navigation fields because of its autonomy and concealment. Existing point-source polarization navigation sensors mainly use a logarithmic amplifier as the arithmetic unit to obtain polarization information. However, these sensors suffer from zero drift and low detection accuracy, which limits their application range. To address the above issues, a polarization navigation sensor based on a differential amplifier is designed as the operational unit. Based on the change of the arithmetic unit of the polarization signal, the algorithm for calculating the heading angle of the sensor is improved. The results of the orientation experiments with the designed sensor in clear weather indicate that the orientation error is ±1.243∘, and the standard deviation is 0.351°. The polarization navigation sensor can extract polarized light information and calculate the heading without accumulation of errors over time accurately and achieves good real-time performance.

Preparation of an Integrated Polarization Navigation Sensor via a Nanoimprint Photolithography Process

Based on the navigation strategy of insects utilizing the polarized skylight, an integrated polarization sensor for autonomous navigation is presented. The polarization sensor is fabricated using the proposed nanoimprint photolithography (NIPL) process by integrating a nanograting polarizer and an image chip. The NIPL process uses a UV-transparent variant template with nanoscale patterns and a microscale metal light-blocking layer. During the NIPL process, part of the resist material is pressed to fill into the nanofeatures of the variant template and is cured under UV exposure. At the same time, the other parts of the resist material create micropatterns according to the light-blocking layer. Polymer-based variant templates can be used for conformal contacts on non-flat substrates with excellent pattern transfer fidelity. The NIPL process is suitable for cross-scale micro–nano fabrication in wide applications. The measurement error of the polarization angle of the integrated polarization sensor is ±0.2°; thus, it will have a good application prospect in the polarization navigation application.

A bio-inspired polarization navigation sensor based on artificial compound eyes

Insect compound eyes are optical systems with small volume and a compact structure. The ommatidia in the dorsal rim area of some insects have polarized vision, which can perceive the polarization pattern of the sky and provide them with navigation information. In this paper, inspired by the polarization-sensitive compound eyes of insects, a bio-inspired polarization navigation sensor based on artificial compound eyes is designed. The sensor consists of an artificial compound eye, an integrated polarization detector and an integrated circuit. The optical path of the sensor uses the lens defocus method, which can ensure that the sensor obtains redundant polarization information. The integrated polarization detector is used to obtain the polarization information of the incident light, and the integrated circuit is responsible for the calculation. To extract effective information from images, we propose a multi-threshold segmentation method to filter and classify effective pixels. We use the least squares method to fit the inherent error of the sensor and then compensate it. The indoor calibration accuracy of the sensor is ±0.3°, and the outdoor calibration accuracy is ±0.5°. The sensor can provide accurate direction information for general smart mobile devices. The size of the sensor is 4 × 4 × 2 cm, and the weight is only 15 g. The key components of the sensor can be mass-produced, and it is a miniaturized and low-cost polarization navigation sensor.

Sensor Modeling and Calibration Method Based on Extinction Ratio Error for Camera-Based Polarization Navigation Sensor.

The performance of camera-based polarization sensors largely depends on the estimated model parameters obtained through calibration. Limited by manufacturing processes, the low extinction ratio and inconsistency of the polarizer can reduce the measurement accuracy of the sensor. To account for the challenges, one extinction ratio coefficient was introduced into the calibration model to unify the light intensity of two orthogonal channels. Since the introduced extinction ratio coefficient is associated with degree of polarization (DOP), a new calibration method considering both azimuth of polarization (AOP) error and DOP error for the bionic camera-based polarization sensor was proposed to improve the accuracy of the calibration model parameter estimation. To evaluate the performance of the proposed camera-based polarization calibration model using the new calibration method, both indoor and outdoor calibration experiments were carried out. It was found that the new calibration method for the proposed calibration model could achieve desirable performance in terms of stability and robustness of the calculated AOP and DOP values.

Study on displacement estimation in low illumination environment through polarized contrast-enhanced optical flow method for polarization navigation applications

Polarization navigation techniques become more and more significant for a wide range of researches and applications. However, most of the polarization navigation sensors can only output the navigation angle information of a carrier based on the angle of polarization (AoP) from the skylight in the daytime; they cannot provide the displacement information in day and night. In this paper, a polarized contrast-enhanced (PCE) optical flow method is proposed to improve the accuracy of displacement estimation and reduce the influence of the ambient brightness. We acquire the degree of linear polarization (DoLP) images during the motion of the carrier in low illumination environment, and the hypothesis of the DoLP continuity is used for the theoretical foundation of this PCE optical flow method under the conditions of parallel light source and small displacements. The displacement calibration on the experimental platform is obtained by using a laser interferometer and spectrometer, and the contrast of the polarimetric image and the calculated polarized optical flow value are used as the validation criteria. Under 0.7198Lx illumination intensity, the cumulative error of the displacement obtained by the PCE method is less than 8 mm and the accuracy of the displacement estimation is almost 2 times higher than that of the traditional Lucas-Kanade(LK) optical flow method. Our experimental results have also shown that under 10°, 10−1, or even 10-2 levels of the standard illumination, the displacement values from the PCE optical flow method are in good agreement with the theoretical values.

Polarized skylight compass based on a soft-margin support vector machine working in cloudy conditions.

The skylight polarization pattern, which is a result of the scattering of unpolarized sunlight by particles in the atmosphere, can be used by many insects for navigation. Inspired by insects, several polarization navigation sensors have been designed and combined with various heading determination methods in recent years. However, up until now, few of these studies have fully considered the influences of different meteorological conditions, which play key roles in navigation accuracy, especially in cloudy weather. Therefore, this study makes a major contribution to the study on bio-inspired heading determination by designing a skylight compass method to suppress cloud disturbances. The proposed method transforms the heading determination problem into a binary classification problem by segmentation, connected component detection, and inversion. Considering the influences of noise and meteorological conditions, the binary classification problem is solved by the soft-margin support vector machine. In addition, to verify this method, a pixelated polarization compass platform is constructed that can take polarization images at four different orientations simultaneously in real time. Finally, field experimental results show that the designed method can more effectively suppress the interference of clouds compared with other methods.

Formation experiment with heading angle reference using sky polarization pattern at twilight.

Consistency has always been an important topic in formation cooperation research. Traditional navigation methods, such as inertial navigation and geomagnetic navigation, have the disadvantages of error accumulation and low stability, thus reducing the consistency of formation. We propose to use the skylight polarization pattern to provide heading angle reference for formation cooperation of multi-agents. The experimental results show that the polarization navigation has good stability and no error accumulation. First, we analyzed the consistency of using the skylight polarization pattern to provide a heading reference for formation experiments. Then, based on the bionic polarization navigation sensor, we measured the difference of the skylight polarization azimuth of different observers at twilight. Further, a mobile robot platform was built with its heading angle provided by a polarization navigation sensor. Finally, we present an overview of a 3-robots platform formation experiment at twilight.

A novel algorithm for estimating the relative rotation angle of solar azimuth through single-pixel rings from polar coordinate transformation for imaging polarization navigation sensors

Polarized skylight provides navigation compass for many polarization sensitive birds and insects. In this paper, a method based on polar coordinate transformation (PCTA) is proposed to use all the polarization information of the polarization angle image. First, a polar coordinate system is set up on the image of angle of polarization (AOP), and then the single pixel ring corresponding to each pole diameter is extracted. After that, the corresponding point of the same pixel value is found from the two consecutive single pixel rings, and the relative rotation angle of the solar meridian is calculated according to the trigonometric relationship. Finally, simulation and outdoor experiments are performed. The algorithm is preliminarily tested and the accuracy of the simulation is in −0.004°∼+0.045°. The outdoor static experiment is carried out on a roof of a building on campus. The experiment shows that the outdoor static experimental precision is within 0.63°. In order to be applied to the estimation of the actual carrier rotation angle, the dynamic application research experiment is carried out. The center region is chosen as the true value of AOP. The error is about −0.7°∼+0.5°. It proves that the proposed algorithm is effective and accurate.

Research on a novel imaging bionic polarization navigation sensor for glimmer environment application

Polarization navigation system is a hotspot in the field of bionic navigation. Compared with point source polarized light navigation sensor, the polarization information acquisition method based on image sensor and imaging technology has better robustness, and it can obtain more polarization information. In this paper, an embedded imaging polarization sensor for glimmer environment application is designed and developed. The multi-channel video processing technology of TMS320DM642 is used to capture the polarization information of charge coupled device (CCD) camera with three channels. The images are processed by digital signal processer (DSP) in real time, and the angle of polarization (AOP) image is calculated simultaneously with an acquisition and calculation speed of 10 frame per second. Sensor can obtain absolute rotation angle, and the AOP image can be displayed on liquid crystal display (LCD). It provides an effective experimental platform for the research of imaging polarization mode navigation device based on embedded system.

Study on polarized optical flow algorithm for imaging bionic polarization navigation micro sensor

At present, both the point source and the imaging polarization navigation devices only can output the angle information, which means that the velocity information of the carrier cannot be extracted from the polarization field pattern directly. Optical flow is an image-based method for calculating the velocity of pixel point movement in an image. However, for ordinary optical flow, the difference in pixel value as well as the calculation accuracy can be reduced in weak light. Polarization imaging technology has the ability to improve both the detection accuracy and the recognition probability of the target because it can acquire the extra polarization multi-dimensional information of target radiation or reflection. In this paper, combining the polarization imaging technique with the traditional optical flow algorithm, a polarization optical flow algorithm is proposed, and it is verified that the polarized optical flow algorithm has good adaptation in weak light and can improve the application range of polarization navigation sensors. This research lays the foundation for day and night all-weather polarization navigation applications in future.

A Bionic Polarization Navigation Sensor Based on Polarizing Beam Splitter

Polarization navigation has been an active research direction in navigation fields due to its autonomy and robustness, especially in global navigation satellite system-denied environment. Most existing bionic polarization sensing schemes employed the linear polarizer as the analyzer. However, the quadrature error between the two sets of mutually orthogonal polarizers is usually inevitable, which may cause the sensor output distortion and directly affect the performance of polarization navigation sensors. In this paper, inspired by the special polarization-sensitive structure of insect compound eyes, a polarizing beam splitter (PBS) based polarization navigation sensor is designed. Concerned with the optical path coupling and extinction ratio inconsistency problem between the transmitted beam and the reflected one of the PBS, the novel sensor model is established, where we introduce a coupling coefficient to solve the problems mentioned above. An algorithm of computing the polarization degree and the polarization azimuth angle is presented based on the model. The unscented Kalman filter calibration method is adopted and the calibration experiments are carried out. Finally, the outdoor static accuracy of the sensor is tested, where the results showed that the sensor designed in this paper achieved high accuracy and good stability for a long time.

Design and Calibration of a Novel Bio-Inspired Pixelated Polarized Light Compass.

Animals, such as Savannah sparrows and North American monarch butterflies, are able to obtain compass information from skylight polarization patterns to help them navigate effectively and robustly. Inspired by excellent navigation ability of animals, this paper proposes a novel image-based polarized light compass, which has the advantages of having a small size and being light weight. Firstly, the polarized light compass, which is composed of a Charge Coupled Device (CCD) camera, a pixelated polarizer array and a wide-angle lens, is introduced. Secondly, the measurement method of a skylight polarization pattern and the orientation method based on a single scattering Rayleigh model are presented. Thirdly, the error model of the sensor, mainly including the response error of CCD pixels and the installation error of the pixelated polarizer, is established. A calibration method based on iterative least squares estimation is proposed. In the outdoor environment, the skylight polarization pattern can be measured in real time by our sensor. The orientation accuracy of the sensor increases with the decrease of the solar elevation angle, and the standard deviation of orientation error is at sunset. Results of outdoor experiments show that the proposed polarization navigation sensor can be used for outdoor autonomous navigation.

Real-time polarization imaging algorithm for camera-based polarization navigation sensors.

Biologically inspired polarization navigation is a promising approach due to its autonomous nature, high precision, and robustness. Many researchers have built point source-based and camera-based polarization navigation prototypes in recent years. Camera-based prototypes can benefit from their high spatial resolution but incur a heavy computation load. The pattern recognition algorithm in most polarization imaging algorithms involves several nonlinear calculations that impose a significant computation burden. In this paper, the polarization imaging and pattern recognition algorithms are optimized through reduction to several linear calculations by exploiting the orthogonality of the Stokes parameters without affecting precision according to the features of the solar meridian and the patterns of the polarized skylight. The algorithm contains a pattern recognition algorithm with a Hough transform as well as orientation measurement algorithms. The algorithm was loaded and run on a digital signal processing system to test its computational complexity. The test showed that the running time decreased to several tens of milliseconds from several thousand milliseconds. Through simulations and experiments, it was found that the algorithm can measure orientation without reducing precision. It can hence satisfy the practical demands of low computational load and high precision for use in embedded systems.

Single-Layer Nanowire Polarizer Integrated With Photodetector and Its Application for Polarization Navigation

We report a method of integrating the single-layer nanowire polarizers with photodetectors, and the fabricated device is used as the polarization navigation sensor. The fabrication processes mainly based on nanoimprint lithography and dry etching. The fabrication method can fabricate nanogratings with multi-orientation simultaneously, so angular alignment error is eliminated. The external quantum efficiency of the integrated device is tested, and a peak external quantum efficiency of 23% at around 440 nm is achieved. The indoor angle output experiment of a navigation sensor is investigated, and the angle output error is tested to be within ±0.1°. The outdoor angle output experiment has also been tested, and the errors are less than ±1.5°. The measurement results show that the fabricated device is suitable for polarization navigation.

A Bionic Polarization Navigation Sensor and Its Calibration Method.

The polarization patterns of skylight which arise due to the scattering of sunlight in the atmosphere can be used by many insects for deriving compass information. Inspired by insects’ polarized light compass, scientists have developed a new kind of navigation method. One of the key techniques in this method is the polarimetric sensor which is used to acquire direction information from skylight. In this paper, a polarization navigation sensor is proposed which imitates the working principles of the polarization vision systems of insects. We introduce the optical design and mathematical model of the sensor. In addition, a calibration method based on variable substitution and non-linear curve fitting is proposed. The results obtained from the outdoor experiments provide support for the feasibility and precision of the sensor. The sensor’s signal processing can be well described using our mathematical model. A relatively high degree of accuracy in polarization measurement can be obtained without any error compensation.

A bionic autonomous navigation system by using polarization navigation sensor and stereo camera

Inspired by the excellent navigational behavior of animals, this paper presents a bionic autonomous navigation (bio-navi) system by using a stereo camera and a polarization navigation sensor (POLNS). A topological graph consisting of nodes and edges forms the core of the system, which is similar to the simultaneous localization and mapping (SLAM). Like most of the SLAM approaches, in the bio-navi system, a node contains pose (position and attitude) and visual template information while an edge represents a constraint between two nodes. The difference is that the POLNS is introduced into the system. The yaw angle obtained from POLNS is attached to a node as a new property and also forms a new edge which restricts the direction of the related node. Besides, an absolute place constraint edge is added to the current node when recognizing a prior known place. To improve the accuracy and robustness of the place recognition, a POLNS-assist loop closure detection method is presented and to correct the pose error of constructed nodes, an improved graph optimization algorithm is derived in detail which is able to make full use of all the constraints. To demonstrate the performance of the system, an outdoor vehicle test has been done, and the results show its effectiveness and feasibility.

Simple integration process of single-layer nanowire gratings for polarization navigation sensor

A simple integration process of single-layer nanowire gratings (SLNGs) for polarization navigation sensor is proposed. The adaptive capacity of the nanoimprint process on uneven substrate is realized using compressed air and the flexible mold. The plasma ashing process is used to simplify the conventional SLNGs fabrication process. Based on the work mentioned above, six SLNGs areas with 1.3 mm×1.3 mm and six different directions are successfully integrated into a polarization sensitive structure applied to a polarization navigation sensor. The measurement result of quantum efficiency shows good sensitivity, and the angle of polarization measurement error is <±0.1 deg. The experiment result shows that the proposed process is applicable for the integration of large-area single-layer nanometal patterns.

Calibration of a polarization navigation sensor using the NSGA-II algorithm

A bio-inspired polarization navigation sensor is designed based on the polarization sensitivity mechanisms of insects. A new calibration model by formulating the calibration problem as a multi-objective optimization problem is presented. Unlike existing calibration models, the proposed model makes the calibration problem well-posed. The calibration parameters are optimized through Non-dominated Sorting Genetic Algorithm-II (NSGA-II) approach to minimize both angle of polarization (AOP) residuals and degree of linear polarization (DOLP) dispersions. The results of simulation and experiments show that the proposed algorithm is more stable than the compared methods for the calibration applications of polarization navigation sensors.

Design and Calibration of a Novel Camera-Based Bio-Inspired Polarization Navigation Sensor

The remarkable ability of animals using the skylight polarization pattern provides a significant inspiration for the autonomous robotic navigation. The bio-inspired polarization navigation approach with advantages of efficiency and reliability has aroused much interesting for experts to perform further research. The sensor of measuring the skylight polarization pattern plays a key role in bio-inspired polarization navigation. A novel camera-based bionic polarization navigation sensor is designed and implemented. We propose a robust measurement method based on the least squares by utilizing all outputs of measurement units. For improving the precision of measurement, the errors of sensor are analyzed, and an effective calibration algorithm is proposed in detail. The experiment results show that the measurement accuracy is improved greatly after calibration. Finally, to evaluate the performance of our sensor, experiments of measuring the actual skylight polarization pattern are performed and compared with the results from the single-scattering Rayleigh theory. The comparison results indicate that our sensor can achieve an effective and accuracy measurement in practice.

Real-time Imaging Orientation Determination System to Verify Imaging Polarization Navigation Algorithm.

Bio-inspired imaging polarization navigation which can provide navigation information and is capable of sensing polarization information has advantages of high-precision and anti-interference over polarization navigation sensors that use photodiodes. Although all types of imaging polarimeters exist, they may not qualify for the research on the imaging polarization navigation algorithm. To verify the algorithm, a real-time imaging orientation determination system was designed and implemented. Essential calibration procedures for the type of system that contained camera parameter calibration and the inconsistency of complementary metal oxide semiconductor calibration were discussed, designed, and implemented. Calibration results were used to undistort and rectify the multi-camera system. An orientation determination experiment was conducted. The results indicated that the system could acquire and compute the polarized skylight images throughout the calibrations and resolve orientation by the algorithm to verify in real-time. An orientation determination algorithm based on image processing was tested on the system. The performance and properties of the algorithm were evaluated. The rate of the algorithm was over 1 Hz, the error was over 0.313°, and the population standard deviation was 0.148° without any data filter.