###### Abstract  
Determining the current position in a forest is essential for many applications and is often carried out using smartphones. Modern smartphones now support various GNSS constellations and multi-frequency analyses, which are expected to provide more accurate positioning. This study compares the static autonomous GNSS positioning accuracy under forest conditions of four multi-frequency multi-constellation smartphones as well as six single-frequency smartphones and a geodetic receiver. Measurements were carried out at 15 different study sites under forest canopies, with 24 measurements lasting approximately 10 min each taken for the 11 GNSS receivers. The results indicate that, on average, multi-frequency smartphones can achieve a higher positioning accuracy. However, the accuracy varies greatly between smartphones, even between identical or quasi-identical tested smartphones. Therefore, no accuracy should be generalised depending on the number of usable frequencies or constellations, but each smartphone should be considered separately. The dual-frequency Xiaomi Mi 10 clearly stands out compared with the other smartphone with a DRMS of 4.56 m and has a 34% lower absolute error than the best single-frequency phone. G 2022  
and trucks [18], the autonomous control of forestry vehicles [19], and many more Precision Forestry and Industry 4.0 purposes [20]. The possible applications of satellite-based position determination in the forestry sector are diverse and steadily increasing. Therefore, the frequency of use of GNSS technology in current forestry activities is quite high, although it varies between countries [6]. However, GNSS position determination based on trilateration requires a free and unobstructed signal connection to the satellites in order to carry out several precise pseudo-range measurements. With its canopy, which influences, blocks, or reflects the satellite signals to a particular extent, the complex forest environment poses a unique challenge to being able to determine exact positions [21; 22; 23]. In the scientific literature, many limitations and influence factors of finding a precise GNSS position under the canopy have been identified and examined. These include forest types [8; 24; 25; 26; 27], dense canopies [28; 29; 30; 31; 32], the water content of leaves and wooden material [33; 34], topography [32; 35], local atmospheric conditions [36], temperatures below freezing [16; 21], seasons [21], wind [21], humidity [27; 37], and many more. The recipient's environment is of crucial importance. Below the canopy, the Multipath effect can significantly affect the accuracy of the positioning. Multipath occurs when a satellite signal arrives at a receiver's antenna via more than one different path. Objects such as trees near the receiver antenna can reflect GNSS signals and, thus, create secondary propagation paths. These secondary path signals can interfere with reaching the receiver directly from the satellite. Multipath affects both pseudo-range and carrier-phase measurements [38]. Particularly, thin branches and leaves as strong Multipath reflectors favour the Multipath, reduce the position accuracy, and disturb the signal-to-noise ratio [21; 39; 40]. In particular, deciduous forests and evergreen forests, where there are tall trees with thick trunks as well as dense crowns, cause high Multipath and poor reception [41]. However, special antennas, for example, polarised or choker ring antennas, which smartphones do not have, can reduce the Multipath effect in shielded areas [23; 42]. Multipath error studies of smartphone positioning accuracy in an anechoic chamber in a controlled environment demonstrated that the quality of observations collected in the anechoic chamber is significantly better than those collected in the natural environment [43]. Performance studies of a Xiaomi Mi 8 smartphone related to pseudo Multipath and noise compared to a geodetic receiver found that the smartphones resulted in higher Multipath and lowered C/N\({}_{0}\) values than geodetic receivers [44].