Tracking foresters and mapping tree stem locations with decimeter-level accuracy under forest canopies using UWB

Abstract

This paper presents a new method for tracking foresters and mapping tree stem locations under forest canopies utilizing ultra-wideband (UWB) data, in which four estimators (collector, estimator, locator, and extractor) operate closely together. The collector records all the distance measurements (beacon to beacon and terminal to the beacons); the estimator determines the local coordinates of the beacons automatically and precisely based on the distance measured between them; the locator then determines the trajectory of the terminal/forester using the extended Kalman filter (EKF) with the assistance of non-line-of-sight (NLoS) distance measurement classification and processing; the extractor continuously determines the optimal locations of the tree stems. To fully evaluate the performance of the developed method, experiments were conducted under four forest canopies with different tree densities and species. The experimental results show that the root-mean-squared-errors (RMSEs) of the proposed method for the terminal/forester positioning and individual tree stem location are less than 0.3 m with a stable update rate of 20 Hz, and a coverage of larger than approximately 3,000 m2 with only four UWB beacons under forest canopies. Therefore, it is sufficient for forest surveys and management with reduced human efforts.