Multipath mitigation under forest canopies: A choke ring antenna solution

Abstract

Evaluating the accuracy of global positioning system (GPS) receivers in applications under forest canopies has become an area of increasing interest. Reducing the error experienced by multipath present under forested conditions has also been a significant concern. We present results of assessing a choke ring antenna solution to the reduction of multipath effects under forest canopies. This system serves to increase the accuracy of positional fixes as well as provide a baseline for assessing multipath effects. We assessed these by comparing results to data collected by separate antenna configurations (yet same receiver) on varying slope positions and canopy conditions. Using a choke ring antenna, we found horizontal position accuracy of differentially corrected data to range from 0.32 to 0.88 m root mean square error reported at 95% confidence across a topographic gradient during leaf-on conditions. Under leaf-off conditions the horizontal position accuracy ranged from 0.35 to 0.69 m. Similar differentially corrected data collected using a standard beacon antenna showed that horizontal position accuracy ranged from 4.9 to 6.1 m during leaf-on conditions and from 3.3 to 5.8 m during leaf-off conditions. When sampled, the data from the two systems were collected within 1 minute of each other; thus, we assume a very similar plane and satellite arrangement. Coupled with topographic factors, a minimum multipath error effect could be determined for this receiver for given site conditions by taking the difference between the two levels of error. For. Sci. © 2009 by the Society of American Foresters.