Assessing the accuracy and integrity of RTK GPS beneath high voltage power lines

Abstract

This paper reports the results of several tests conducted at the University of Southern Queensland (USQ) to determine the frequency with which initialisation failures occur in the Trimble 4700 RTK receivers when operating beneath high voltage power lines. Anecdotal evidence from some practitioners suggested that problems were experienced when measuring beneath high voltage power lines. Some surveyors had reported quite large anomalies. Still others had reported no problems beneath high voltage power lines. Consequently, these tests were designed to provide an empirical evaluation of both the probability of initialisation failure under these conditions, and the range of the subsequent errors in observed coordinates. Observations were also carried out in 'ideal' physical environments to provide an assessment of the general accuracy and reliability of RTK GPS and to use as a benchmark for analysing subsequent test results. An attempt has been made to investigate reasons for discrepancies and, although some conclusions have been drawn, these are of a general nature only. Supplementary testing and analysis is being conducted at the USQ to further isolate some of the possible anomalies and to allow statements that are more definitive to be made. Results from field observations indicate that under 'ideal' conditions, the Trimble 4700 RTK GPS Receiver is capable of consistently achieving accuracy within manufacturer's specifications. However the presence of electromagnetic interference and multipath have been shown to significantly impair the process of ambiguity resolution. The conclusions will be of value to individuals who are planning to carry out RTK measurements beneath high voltage power lines, or other areas in which significant electromagnetic fields or multipath may be present.