GPS accuracy part 2: RTK float versus RTK fixed

Kevin W. Hall, Pietro (Peter) Giuseppe Gagliardi, Donald C. Lawton

During the University of Calgary's 2010 geophysics field school, geophone and source point locations for a 3C-2D seismic line were GPS surveyed by student crews over a period of many days. In the course of the RTK GPS (real time kinematic global positioning system) survey, some geophones were surveyed up to three times, particularly in problem areas on the line. In this case, the problem areas had thick bushes and trees, such that the GPS rover was not able to achieve a good GPS solution due to signal attenuation by the vegetation. Comparisons of the repeated data points show that RTK fixed solutions have the best repeatability (accuracy better than one decimeter). RTK float solutions can be as repeatable as fixed solutions, but can also be out by up to five meters, with no way to tell unless surveying a known point. The authors recommend RTK fixed solutions for small station/receiver spacings. FIG. 1. Typical daily GPS base station setup, looking roughly southwest. The part of the seismic line that is visible in this picture is high-lighted with a red line. CREWES Research Report -- Volume 22 (2010) 1 Hall, Gagliardi, and Lawton