Real-time Georeferencing of Thermal Images using Small Fixed-Wing UAVs in Maritime Environments

Abstract

This article considers real-time georeferencing using a fixed-wing unmanned aerial vehicle (UAV) with a thermal camera. A flexible system for direct georeferencing is proposed without the need for ground reference points. Moreover, as the system is tailored for highly maneuverable and agile fixed-wing UAVs, no restrictions on the motion are assumed. The system is designed with a solution for accurate time synchronization between sensors. This feature enables tracking of objects with low uncertainty. Sensors for navigation, permitting estimation of the UAV pose with a nonlinear observer, are employed in addition to a thermal camera. The estimated UAV pose is utilized in georeferencing to acquire Earth-fixed coordinates of objects. The main examples studied in this research are georeferencing of a static object and of a moving marine vessel. To obtain the desired accuracy, thermal camera calibration and compensation of mounting misalignment errors are discussed. The entire system is validated in two independent field experiments with a thorough analysis of the results. Georeferencing of a static object is conducted with centimeter accuracy when the average position of all measurements is used. The position of a moving marine vessel is obtained with mean accuracy of two meters.