# Evaluation of Positioning Accuracy of Smartphones under Different Canopy Openness
###### Abstract
Branches, trunks, and leaves will attenuate, distort, or hinder the forest GNSS signal, so positioning accuracy is significantly lower than those in areas with high openness [28; 29; 30; 31; 32]. Previous research on GNSS receivers in forestry found that the positioning accuracy is the lowest in coniferous forests, middle in broad-leaved forests, and the highest in non-forest lands. The average positioning accuracy increases from the valley and hillside to the top of the mountain [33]. Mountainous and steep-terrain environments also pose some obstacles to accurate GNSS positioning. The research is confirmed by [PERSON] et al. [23]. [PERSON]'s research shows that canopy coverage and open sky have a more significant impact on positioning accuracy than slope degree, slope position, aspect, tree height, canopy depth, or altitude [34]. In addition, [PERSON] et al. [31] and [PERSON] [35] found that the measurement error of GNSS under the forest increases with the breast-height sectional area of the stand. Compared with the open environment, the forest environment is more complex and the positioning accuracy will be affected by many factors. Therefore, many scholars have tried new positioning methods, such as differential global positioning systems (DGPSs), to improve the accuracy of positioning in the forestry environment [28; 36; 37]. Currently, the most used positioning instruments for forestry workers in field surveys are smartphones and low-cost receivers (recreational-grade and map-grade receivers) [38]. Smartphones occupy most of the market for low-cost receivers due to their portability and versatility [39]. More and more forestry work is carried out with smartphones as positioning tools. [PERSON] et al. used smartphones to collect forest canopy hemispheric images [40]. [PERSON] et al. evaluated the measurement of forest sample plots by smartphone applications [41]. [PERSON] et al. used smartphones to measure the wind damage area in the forest [42]. Furthermore, in a study using smartphones to evaluate the positioning accuracy under the forest, [PERSON] et al. used three smartphones to obtain the positioning accuracy of 6.74-11.45 m (with leaves) and 4.51-6.72 m (without leaves) under the forest [42], used dual-frequency smartphones to obtain the positioning accuracy of 6.13 m (with leaves) and 4.10 m (without leaves), and evaluated the applicability of the original GNSS data [43]. [PERSON] et al. measured, in the forest environment (with leaves), that the accuracy of smartphones in PPP mode is equivalent to that of recreational-grade GNSS devices and the distance root means squared (DRMS) of medium and high-canopy openness can reach 2.6-4.2 m [44]. However, little research focuses on comparing positioning accuracy between smartphones and GNSS devices at all levels under the forest. As a result, it is unclear whether the real-time measurement results of smartphones and the data results processed by the PPP mode in the forest environment can achieve satisfactory accuracy. Therefore, it is necessary to quantify the positioning accuracy of smartphones in the forest and to investigate the usability of smartphone positioning in the forest environment. This study aims to quantify the positioning accuracy of smartphones and receivers of various levels in different forest environments by accessing parameters, such as the number of satellites, signal quality, and positioning accuracy. By comparing the differences in positioning accuracy between smartphones and receivers of various levels, we can comprehensively evaluate whether smartphones meet the positioning requirements of forestry work and provide reference opinions for selecting positioning and navigation equipment in different forest canopy openness environments.