The influence of tree canopy on GPS positioning accuracy

Accurate outdoor localization in vegetation-rich environments remains a significant challenge for satellite-based positioning systems. Tree canopy and dense foliage degrade GPS signal quality and may considerably reduce positioning accuracy, especially in applications related to smart mobility and assistive navigation systems. This study investigates the influence of tree canopy on GPS positioning accuracy in a park environment using a smartphone-based GNSS receiver. Experimental measurements were performed at five locations under two different seasonal conditions: with foliage and without foliage. The obtained positioning data were analyzed using several statistical indicators, including variance, cumulative distribution functions (CDF), Circular Error Probability (CEP), R95, DRMS, and carrier-to-noise ratio (C/N). The results showed that positioning errors in the presence of foliage were between 1.86 and 3.66 times higher compared to measurements performed without foliage at most measurement positions. Average positioning variance increased from 1.54 m 2 without foliage to 5.99 m 2 with foliage. In addition, foliage reduced the carrier-to-noise ratio of received satellite signals, and C/N values below 30 dB-Hz were observed more frequently in dense canopy conditions. The results also indicate that foliage has a stronger influence on signal quality than on the number of visible satellites. The obtained results confirm that tree canopy significantly affects GPS localization accuracy and signal reliability in outdoor environments. The study contributes to a better understanding of GNSS performance degradation in vegetation-rich areas and may be useful in the development of outdoor assistive mobility and navigation systems.