How does Global Positioning System (GPS) work?
The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. How accurate is GPS? Civilians have access to the Standard Positioning Service (SPS). The SPS accuracy was intentionally degraded by the Department of Defense in 1994 to 100 meters. This inaccuracy is not a problem when fishing oil rigs offshore. It does present problems when trying to locate wrecks or other subsurface structure. It also creates a problem when using a GPS with a mapping display while fishing in the marsh. What is DGPS and how accurate is it? Differential GPS (DGPS) is a system designed to correct the various inaccuracies in the GPS system. Differential GPS involves the cooperation of two receivers, one that’s stationary and another that’s roving around (your boat) making p
