# Evaluation of Positioning Accuracy of Smartphones under Different Canopy Openness
###### Abstract  
This study focuses on evaluating the positioning accuracy of smartphones in a deciduous forest environment compared to various levels of Global Navigation Satellite System (GNSS) devices. In a mixed coniferous forest with 90% broad-leaved forest (deciduous season), the accuracy of 57 test points was evaluated according to different openness levels under the forest. Taking the coordinates obtained by survey-grade GNSS devices in RTK (Real-time Kinematic) mode as standard, the accuracy of the single-point positioning (SPP) mode and precise-point positioning (PPP) mode obtained by three smartphones (one single frequency and two dual frequency), one survey-grade receiver and one recreational-grade receiver are compared. It can be found that there was a significant positive correlation between canopy openness and carrier-to-noise density(C/N0) (\(p<0.05\)). Meanwhile, the C/N0 of survey-grade devices is significantly higher than that of smartphones. The results show that the positioning accuracy of dual-frequency smartphones under forests is better than that of single-frequency smartphones. Furthermore, the positioning accuracy of the smartphone corrected by PPP mode is better than that of the recreational-grade GNSS receiver and can achieve an accuracy of about 2.5 m in the horizontal direction, which can be used for forestry takeout, reset and determination of forest area boundaries in environments with high openness (R \(>\) 0.7). However, in an environment with low openness (R \(<\) 0.7) and relatively complex forest area positioning, survey-grade GNSS devices are still required to cooperate with the PPP or real-time differential positioning method to obtain accurate sub-meter-level positioning data. achieve better accuracy of street positioning in the urban environment [8]; [PERSON] et al. evaluated the data sampled by GNSS antennas based on smartphones to achieve centimeter precision positioning [9]. In 2016, Google released the original observation data of Android smart devices, which provides a new idea for researching GNSS navigation and positioning technology based on smart terminals. Scholars can calculate and correct the original positioning data obtained by the intelligent terminal through algorithms or other technologies to improve the accuracy of the equipment [10; 11; 12]. In 2018, smartphones were first equipped with dual-frequency GNSS chips. Before that, smart terminals were generally equipped with single-frequency and multi-constellation GNSS chips [13; 14; 15]. The development of dual-frequency chips has promoted the rapid application of precise smartphone positioning in the mass market [16; 17] and increased the adaptability of smartphones in complex environments. Many scholars' positioning tests on smartphones show that the original measurement quality of dual-frequency GNSS smartphones is generally better than that of single-frequency smartphones. Combining RTK (real-time kinematic) and PPP (precise-point positioning) technology can effectively improve the positioning performance of smartphones [18; 19]. The increasingly sophisticated navigation system has played a significant role in forestry, enabling macro control of forest areas and ensuring forestry work's modern and efficient development. Nevertheless, the complicated environment in the forest is undoubtedly a challenge to precise positioning. Due to the complex and diverse forest environment, the signal quality collected by forestry workers using receivers will be affected by terrain or tree canopy [20]. Furthermore, multipath effects will occur when the devices receive space satellite signals due to obstacles (such as tree trunks) between the line and the satellite [21; 22]. That will cause significant errors in positioning calculation and even make it impossible to locate [23; 24]. Relevant research shows that the complex forest environment has a tremendous adverse impact on receiving the signal by GNSS devices [25; 26; 27].