The Global Positioning System was designed by the U.S. Department of Defense to be a military system. Academic institutions throughout the world figured out how to use that military system for very precise applications by using two GPS receivers at a time rather than the military design for using only one GPS receiver. The problem with a two-receiver (“differential”) solution is that one receiver must be placed at a previously known location that has already been surveyed by the government as a reference point, and that GPS receiver must not move while the other “mobile” unit is moved about during a survey. That one reference point usually needs to have a baby-sitter stay there to guard it from being disturbed, and the reference receiver along with the babysitter present a significant cost to the surveyor. The LSU GULFNet solves that two-receiver problem by providing reference stations throughout the State of Louisiana on a 24/7 basis to Land Surveyors with a data cellphone and a single survey-grade GPS receiver!
GPS receivers come in a variety of shapes, styles, applications, and prices. Most people are familiar with the units that are for providing directions in vehicles as well as cellphones and shirt-pocket receivers intended for hiking, hunting, and ones integrated with fish finders. Consumer-grade GPS receivers can generally provide positional information that is good to perhaps 20 to 30 feet. Land Surveyors are generally involved with more elaborate receivers designed for high-accuracy applications that can provide precisions on the order of fractions of an inch. Priced at many tens of thousands of dollars, these survey-grade receivers can receive one, two, or more frequencies from a variety of positioning satellites including American GPS satellites, Russian GLONASS satellites, and eventually various other planned satellite providers.