GPS is an acronym for Global Positioning System, a system of satellites in orbit above the earth that communicate positional information to the surface using microwave frequencies.This information can be interpreted on the ground by a microwave receiver (such as a hand-held GPS or even GPS-equipped cell phone) into very accurate positional information. The accuracy is dependent on a number of factors including how much open sky is visible. Generally accuracy for civilian handheld GPS systems is about 15 meters (50 ft.). While this level of accuracy is sufficient for many applications, it is not nearly enough for mapping bones in a quarry!
Special differential RTK (Real Time Kinematic) GPS equipment has been developed for surveying purposes that can be accurate to millimeters (less than 1/4 of an inch).This equipment includes two complete systems. The first of these is the Base, shown in the picture above. It consists of a satellite antenna (saucer-shaped disk atop tripod), a computer (dark blue case below antenna), a radio (blue box in Justin’s hand) and a radio antenna (atop yellow pole out of picture). The Base is set up on a tripod at a precisely known location. The antenna reads the data from the GPS satellites and the computer determines a position which it compares with its known location. It then sends corrective information out over the radio.
The other system, the Rover, shown at right in the quarry, also consists of a satellite antenna (the disk atop the pole), a computer, a radio (in the blue box with the computer), a radio antenna (the portion of the pole separating the satellite antenna from the blue box) and a field computer to determine the results of the positional data and to store the values (attached to the pole in Justin’s hand).The data transmitted from the base are used to correct the satellite data. As a result, the Rover can determine its position in space with great accuracy. We use the Rover in the quarry to obtain points on the surface of each bone we find. These points can be used later to build the quarry map. The diagram below illustrates the remarkable precision of the GPS equipment. Ten points taken at one time at one pole position are plotted in a square centimeter. This is typical for the system we use.
To learn more about how the GPS data are used to reconstruct the quarry, click here or on “How to Reconstruct a Dinosaur Quarry” in the box in the upper left corner of this page.