A Fisheye Camera System for Polarisation Detection on UAVs

Abstract

We present a light-weight polarisation sensor that consists of four synchronised cameras equipped with differently oriented polarisers and fisheye lenses allowing us to image the whole sky hemisphere. Due to its low weight and compact size it is well-suited as a biomimetic sensor on-board a UAV. We describe efficient methods for reconstruction of the full-sky polarisation pattern and estimation of sun position. In contrast to state-of-the art polarisation systems for UAVs that estimate sun azimuth only, our approach can determine sun elevation as well, even in the presence of clouds and for significant pitch and roll angles of the UAV. The calibration and registration of the four fisheye cameras is achieved by extending an existing omni-directional calibration toolbox to multi-camera calibration. We present examples of full-sky reconstruction of the polarisation pattern as well as an analysis of the error in the sun position estimate. In addition, we performed a preliminary test on-board a quadcopter.