The accuracy of GPS for wildlife telemetry and habitat mapping

Summary 1 Decision support tools used for vegetation management require accurate information on the spatial array of different plant communities and a herbivore’s grazing location. We tested the accuracy and precision of locations derived using the satellite navigation global positioning system (GPS). 2 Before May 2000, the accuracy and precision of GPS-derived locations were degraded by a process known as selective availability (SA); after May 2000, SA was disabled. In this study we investigated how to handle and improve the quality of data generated both when SA was enabled and when SA was disabled using relative GPS (rGPS). rGPS entails the post-processed correction of the roving GPS module with simultaneously acquired positional errors recorded at a known stationary reference location. 3 With SA enabled, GPS data were obtained at a fixed known location to obtain baseline information, and from a roving module that essentially mimicked surveying techniques or the movement of a free-ranging animal. The mean accuracy of GPS with SA enabled was 21 m for the fixed module and 25 m for the roving module. Use of rGPS and further manipulation of the data improved the mean accuracy of the data to 7 m for the fixed module and 10 m for the roving module. With SA disabled, data were similarly recorded from the fixed known location and resulted in a mean location accuracy of 5 m. The use of rGPS resulted in a significant improvement of this value to 3·6 m and precision measured by the 95% quantile was < 10 m. For mapping and wildlife tracking, such quality in terms of location accuracy and precision is unprecedented and demonstrates that rGPS may still be useful in many applications. 4 GPS enables the world-wide collection of accurate and precise location information at 1-second intervals. Furthermore, by programming the GPS receiver to overdetermine location by using information from all visible satellites, many of the limitations that arise in habitats or environments with a limited view of the sky may be overcome. 5 With SA now disabled, the potential use of GPS will increase. With further miniaturization, surveying of remote featureless landscapes or the tracking of crepuscular or far-ranging animals will become more accurate and more quantifiable than ever before.

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