Effects of forest thinning on static horizontal position accuracy collected with a mapping-grade GNSS receiver

Resumo

The static horizontal position accuracy of a mapping-grade GPS receiver was tested in two different pine forest conditions (pre-thinning and post-thinning of a 20-year old loblolly pine (Pinus taeda) stand). The main objective of this study was to describe the horizontal position error that might be observed shortly before and shortly after a thinning operation. In general, by using the Trimble Juno T41 series receiver, we found the static horizontal position error prior to thinning averaged 4.14 m when each individual point was assumed to be as a sample. When the northing and easting values of each epoch were averaged, the error was 1.57 m. A few days after thinning, the horizontal position error averaged 2.32 m for individual samples, and 1.02 m when the northing and easting values were averaged. Subsequent post-thinning measurements showed further improvements in static horizontal position accuracy. The static horizontal position error was 1.33 m 9 days later (0.52 m if northing and easting values are averaged) and 2.29 m 14 days later (0.58 m if northing and easting values are averaged). Therefore, findings suggested that the magnitude of horizontal position error decreased after the thinning operation. Further, according to rose diagrams representing the direction of error, the general direction of pre-thinning error seems different than the direction of post-thinning error, and there is some agreement that the post-thinning positions captured have the same general direction of error. Therefore, the quality of the data and the density of the trees around the data collection area are dependent.