Abstract
The Global Positioning System (GPS) is a navigation system consisting of a constellation of 24 satellites in 6 orbital planes that provide accurate 3-dimensional position and velocity as well as precise time to users anywhere in the world 24 hours a day.
User receivers measure their apparent range to the satellites by processing the received signals to determine transit time and correcting for atmospheric delay using stored and broadcast models. Since the location of the satellites, at the time of signal transmission, is known from the broadcast ephemeris, the location of the receiver can be triangulated from the range measurements.
Similarly, the user receiver’s velocity can be solved by comparing the measured Doppler shift of the received signals to the expected Doppler shift based on the satellites velocity vector, calculated from the ephemeris, projected on the line of sight to the satellite. After the receiver’s clock error is eliminated, by over determination, the residual Doppler is attributed to the user velocity.
The viable utilization of the GPS in the Appalachian Oilpatch comes from the ability to take small handheld units, the size of a pocket calculator, to the field to quickly position by latitude and longitude or by UTM the location of fixtures or facilities for which there is no surveyed data (examples would include older non-platted wells, the location of old pipeline systems and the location of new well roads that are not yet shown on topographic or company maps). This data can be obtained and stored in the field and later downloaded to mapping software such as AutoCad.
The system can be used in reverse with surveyed positions uploaded into the GPS system in the office before leaving for the field and then using the navigation capabilities of the GPS unit to lead you to the surveyed location or site.
The simplicity of use together with the low cost and pocket size makes a GPS unit one more viable tool for the field engineer or geologist.
