Standard and real-time accuracy and reliability of a mapping-grade GPS in a coniferous Western Oregon forest

Abstract

Accuracy requirements for forested resource measurements can vary greatly depending on analysis and management objectives. Technologies that present efficiencies for reliable measurement collection may help organizations better meet data requirements. We tested the accuracy and reliability of a mapping-grade GPS in a variety of forested conditions in western Oregon. Our objectives were to measure the performance of a GPS operating in a standard configuration and also with real-time US Coast Guard Beacon signals. We also examined the influence of postfield differential corrections and the number of GPS points collected on measurement accuracy and reliability. We found measurement accuracies between 1 and 4 m from true position depending on the amount of canopy closure and the type of GPS configuration. Our results indicated that both standard-mode GPS and US Coast Guard Beacon signals can produce very accurate measurements in open-canopy conditions but are less reliable in young-forest conditions. Postprocessing of field measurements generally yielded improved measurements in young-forest settings but led to slightly reduced accuracies for US Coast Guard Beacon data collected in open-canopy settings. Our results also indicated that collecting a greater number of points does not necessarily lead to improved measurement accuracies. Copyright © 2006 by the Society of American Foresters.