Highly accurate survey-grade Global Positioning System (GPS) technology was used at the two Osage-Skiatook petroleum environmental research sites to document the locations of observation wells, geoprobe holes, and other sampling sites of 15 research scientists. Real-time kinematic (RTK) GPS was the method used, because it is stable, fast, and accurate.
Initially three survey monuments were installed one at each research site and one at the U.S. Army Corps of Engineers headquarters for Skiatook Lake. The monument locations were established by static GPS surveys that occupied each of the sites for four hours. The data were submitted to the NOAA-National Geodetic Survey (NGS) Online Positioning User Service (OPUS) for processing. OPUS processes the data relative to three sites on the NGS continuously operating reference station network (CORS). CORS provides GPS carrier phase and code range measurements in support of three-dimensional positioning activities throughout the United States. OPUS enables positioning accuracies, both horizontally and vertically, that approach a few centimeters relative to the National Spatial Reference System and electronically mails the results to the sender. The usual turnaround time for a data set is 2-3 minutes, depending upon the file size. Static GPS surveys are highly accurate, but require post processing the data and longer occupation time.
The RTK surveys require a GPS base station positioned over a known monument, a GPS rover, and a radio link between the base station and the rover. The radio link transmits the base station correction data to the rover. The rover combines the base station data with the rover GPS data to produce real-time coordinates. The rover must maintain lock on at least four of the same satellites that the base station is tracking. Each survey location is occupied for 3 minutes. Setup time at each location is less than a minute, if the rover maintains lock on the satellites and the radio link to the base station.
Accuracy in the horizontal component is 1 centimeter (cm) plus 2 parts per million (ppm) times the baseline distance and in the vertical component is 2 cm plus 2 ppm times the baseline distance. The calculated accuracy for the initial static GPS surveys that occupied the survey monuments ranged from 1.2 to 1.4 cm for the horizontal component and 2.2 to 2.4 cm for the vertical component. Calculated accuracy for the RTK surveys at the research sites are about 2.2 to 2.4 cm for the horizontal component and 4.2 to 4.4 cm for the vertical component.