A Lightweight Single-Camera Polarization Compass With Covariance Estimation

A lightweight visual compass system is presented as well as a direct method for estimating sun direction and its covariance. The optical elements of the system are described enabling estimation of sky polarization in a FOV of approx. 56 degrees with a single standard camera sensor. Using the proposed direct method, the sun direction and its covariance matrix can be estimated based on the polarization measured in the image plane. Experiments prove the applicability of the polarization sensor and the proposed estimation method, even in difficult conditions. It is also shown that in case the sensor is not leveled, combination with an IMU allows to determine all degrees of orientation. Due to the low weight of the sensor and the low complexity of the estimation method the polarization system is well suited for MAVs which have limited payload and computational resources. Furthermore, since not just the sun direction but also its covariance is estimated an integration in a multi-sensor navigation framework is straight forward.