Assessing Point Accuracy of DGPS Under Forest Canopy Before Data Acquisition, in the Field and After Postprocessing

Abstract

A low-cost, hand-held, 10-channel, single-frequency G lobal Positioning System (G PS) receiver observing pseudorange and carrier phase was used to determine the positional accuracy of 35 points under tree canopies. The mean position error based on differential postprocessing ranged from 0.49 to 3.60 m for 2 -20 min of observation at points with basal area B 30 m 2 ha ¼ 1 . F or points with basal area ] 45 m 2 ha ¼1 the mean position error ranged from 2.15 to 5.60 m. R egression analysis revealed that basal area and observation period were the most signi cant factors to predict the position error that could be obtained by G PS data collection before or during data acquisition (R 2 ¾ 0.37). After differential postprocessing, the most signi cant factors to predict position error were the standard deviation reported by the postprocessing software and whether both pseudorange and carrier phase were used to compute the coordinates or pseudorange only (R 2 ¾ 0.57). The position error decreased with decreasing density of forest, increasing length of observation period, decreasing standard deviation, and combined use of pseudorange and carrier phase.

Assessment of Low-Cost GPS Receiver Accuracy and Precision in Forest Environments

“…Although horizontal accuracies below 1 m have been reported in previous studies ͑Naesset et Naesset 2001͒, these involved using differential postprocessing methods ͑Naesset 2001; Jonmeister 2002͒ andGPS-GLONASS receivers ͑Naesset et al 2000;Naesset 2001͒, while in this study only lowcost, real-time, hand-held GPS receivers were used, so that neither postprocessing nor long time observations were required. Vertical accuracy ranged from 6.80 to 8.50 m depending on the GPS model.…”

“…Research regarding end-user practical recommendations has focused on determining GPS receiver performance under different forest conditions by comparing receivers ͑Karsky et al 2000; positioning methods ͑Naes-set et al 2000;Naesset and Jonmeister 2002;Hasegawa and Yoshimura 2003;Sawaguchi et al 2003͒. Techniques such as differential global positioning system ͑DGPS͒ improve precision and accuracy under tree canopies ͑Hasegawa and Yoshimura 2003; Sawaguchi et al 2003;Satirapod et al 2003; Tiberius and Kenselaar 2003͒ but they are not available for recreational GPS receivers, which are cheaper, easier to use, and require less user training than topographic GPS receivers.…”

Monitoring of Forest Hauling Roads Wearing Course Damage Using Unmanned Aerial Systems

“…Abdi et al (2012) published the horizontal accuracy of GPS for forest mapping as a variable and in their study, values ranged from 6.49 to 88.03 m, depending on the GPS signal or barriers. This is a general problem when using GPS under forest canopies and some authors (Naesset &, Jonmeister 2002) see the solution in a longer observation time period and applying DGPS. Other studies have shown big variable average accuracies due to the diff erent methods and GPS receivers (August et al 1994, Wolniewicz 2001, Rodríguez-Pérez et al 2007.…”

Behavior of GPS Signal Interruption Probability under Tree Canopies in Different Forest Conditions

“…Researchers have studied the problem with the aim of identifying the factors most strongly associated with this interference and providing better positioning and error estimates under tree canopies. Naesset and Jonmeister [2002] found that reduction of basal area as well as longer survey periods increase positional accuracy. Kobayashi et al [2001] agreed and suggested the selective use of point positioning and differential GPS techniques to improve accuracy.…”