USING ROCKET SCIENCE TO STUDY ROCK SCIENCE
TURNER, Lawrence E, Math/Physical Science Department,
turner@swau.edu
CHADWICK, Arthur V, Geology Department, Southwestern
SPENCER, Lee, EHRC,
The Global Positioning System (GPS) has become a standard
method of locating one's position on the earth. The modern paleontologist who
hopes not to become extinct must be familiar with this technology. While it is
not necessary to be a GPS expert, it is useful to understand how GPS works and
how current paleontological research can be enhanced
by utilizing this increasing indispensable tool.
The handheld GPS units are quite inexpensive and serve to
determine locations to within 5 m. While this is satisfactory for recording a
general location, it cannot be used for the precise determinations needed in a
fossil quarry. Fortunately, standard high-precision surveying GPS equipment is
available that has a precision of less than 1 cm. To achieve the spectacular
results that GPS is capable requires the application of modern technology and
physics. The simple handheld units use Einstein's General Theory of Relativity!
The GPS utilizes a constellation of satellites in
half-sidereal day orbits transmitting information on two frequencies. The data
is encoded in such a way that the distance to each satellite can be computed
using a simple passive multi-channel receiver with an inexpensive clock. The
detection and capture of four satellites permits the computation of the clock
error and the location of the unit in three-dimensions.
The use of two frequencies permits correcting for the major
effects of the variable propagation delay of the signals as they pass through
the ionosphere. Utilizing a base station with a known location that receives the
satellite information and transmits corrections to a rover unit that is
simultaneously receiving information from the same set of satellites provides a
more precise location of the rover. Applying phase information of the carrier
frequencies finally permits the desired sub-centimeter precision.
While this equipment has been designed for high-precision surveying problems and is typically used for obtaining surface topology, the precision achieved allows the measurement of individual fossils. The location data is recorded and saved in a digital format that permits direct input into GIS software for analysis and display.