Abstract
Elevation or height differences are necessary measurements for many forest operation activities. We rigorously examined the vertical measurement performance of five mapping-grade GPS receivers in three forest settings representing open-sky,young-forest, and closed-canopy conditions. The mapping-grade GPS receivers collected data simultaneously at each of the three forest settings and had different hardware and data-collection configurations, including internal and external antennas, and real-time differential corrections. We evaluated the influence of forest setting and postprocessed differential corrections on all GPS receiver measurements, including those that were collected with real-time differential corrections. We also compared the effect of 1-, 30-, and 60-point averaging intervals on vertical measurement accuracy. We found average vertical accuracies for unprocessed GPS receiver measurements of 0.9, 1.7, and 2.8 m in the open-sky, young-forest, and closed-canopy settings, respectively. The influence of data postprocessing was inconsistent under closed canopy and resulted in average vertical GPS accuracies of 0.2, 0.4, 3.3 m in open-canopy, young-forest, and closed-canopy settings, respectively. Different point averaging intervals did not result in statistically significant differences in vertical accuracies for either unprocessed or postprocessed GPS data.