An Efficiency Evaluation of the Glaobal Positioning System under Forest Canopies

Authors: John Firth, Rod Brownlie
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 1998, Issue N.Z.J.For. 43(1) 1998, pp 19-25, May 1998
Publisher: New Zealand Institute of Forestry

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Abstract: The Global Positioning System (GPS) is commonly used to provide coordinates for updating forest maps. In open situations, i.e. where the signals are not influenced by tall trees, buildings and hills, the coordinates can usually be obtained in an accurate and timely manner. When used under a forest canopy, however, the extent to which the canopy may reflect or block GPS satellite radio signals has not yet been determined.

The effectiveness of two models of GPS receiver in defining point locations and wads, was compared in the open and in or near areas of radiata pine, Douglas-fir and indigenous forest. These types of tree canopy were found to affect signal reception and hence the efficiency of both receivers.

Used in both static and roving mode, for mapping point locations and forest roads in the open, both instruments performed well. However, when used under forest canopies both receivers were less efficient, either because communication with the satellites was temporarily lost or because, in some instances, it could not be established at all over a 10 minute data collection period.

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