Accuracy of Kinematic Positioning Using Global Satellite Navigation Systems under Forest Canopies

TLDR

A harvester equipped with integrated measurement apparatus can collect detailed roundwood data during operations, but its positional accuracy is currently insufficient to match remote sensing accuracy for individual trees. The study aims to evaluate the accuracy of GNSS‑based positioning instruments moving under forest canopies of varying densities to assess the current state of the art. The authors conducted tests on an all‑terrain vehicle equipped with GNSS and IMU, measuring 224 tree positions with a total‑station and RTK GPS as references, and determining the vehicle’s position with GNSS‑IMU achieving 0.7 m 2D RMSE. Single‑frequency GNSS receivers yielded 2D RMSE of 4.2–9.3 m, largely unaffected by canopy density, whereas dual‑frequency receivers were highly sensitive to satellite visibility but achieved substantial accuracy gains when post‑processed with IMU data.

Abstract

A harvester enables detailed roundwood data to be collected during harvesting operations by means of the measurement apparatus integrated into its felling head. These data can be used to improve the efficiency of wood procurement and also replace some of the field measurements, and thus provide both less costly and more detailed ground truth for remote sensing based forest inventories. However, the positional accuracy of harvester-collected tree data is not sufficient currently to match the accuracy per individual trees achieved with remote sensing data. The aim in the present study was to test the accuracy of various instruments utilizing global satellite navigation systems (GNSS) in motion under forest canopies of varying densities to enable us to get an understanding of the current state-of-the-art in GNSS-based positioning under forest canopies. Tests were conducted using several different combinations of GNSS and inertial measurement unit (IMU) mounted on an all-terrain vehicle (ATV) “simulating” a moving harvester. The positions of 224 trees along the driving route were measured using a total-station and real-time kinematic GPS. These trees were used as reference items. The position of the ATV was obtained using GNSS and IMU with an accuracy of 0.7 m (root mean squared error (RMSE) for 2D positions). For the single-frequency GNSS receivers, the RMSE of real-time 2D GNSS positions was 4.2–9.3 m. Based on these results, it seems that the accuracy of novel single-frequency GNSS devices is not so dependent on forest conditions, whereas the performance of the tested geodetic dual-frequency receiver is very sensitive to the visibility of the satellites. When post-processing can be applied, especially when combined with IMU data, the improvement in the accuracy of the dual-frequency receiver was significant.