Global Positioning System (GPS)

The Global Positioning System, or GPS, finds a location on Earth by using satellites and radio signal timing. It changed how people navigate and how many industries work. GPS was developed in 1978 by the U.S. Department of Defense for military use. It became available for civilian use in 1983.

GPS satellites orbit in medium Earth orbit about 20,200 kilometers above Earth. Each satellite takes about 11 hours and 58 minutes to complete one orbit. A full GPS constellation has 24 satellites, which...

GPS accuracy can change because of signal delays, reflections, and device problems. These errors come from the atmosphere, nearby surfaces, satellites, and the receiver itself. To get reliable positioning, GPS systems must reduce these effects as much as possible.

As GPS signals pass through the ionosphere and troposphere, they slow down. The ionosphere contains charged particles and is strongly affected by solar activity. The troposphere contains water vapor, which also changes how the signal...

Earth shape and GPS height models are explained using the ellipsoid, the geoid, and modern coordinate systems. The Earth is best described as an ellipsoid, which is a slightly flattened sphere formed by rotating an ellipse around its minor axis. This flattening makes the polar axis about 21 kilometers shorter than the equatorial axis.

The geoid shows a different side of Earth’s shape. It is the Earth’s gravitational shape and matches mean sea level, or MSL. The geoid is an irregular...

Global Positioning System (GPS) helps map field locations for surveying, navigation, and infrastructure work. Satellite signals let a GPS receiver find an object’s position very quickly, often in less than a second. This speed makes GPS a practical tool for fieldwork.

Modern GPS receivers are small, light, and energy efficient. They are built for portable use in real field conditions. GPS signals use the microwave spectrum, so they can work in rain and fog. Even so, ionospheric disturbances...

GPS surveying uses different methods to balance accuracy, speed, and field conditions. The main approaches are static GPS, kinematic GPS, and real-time kinematic (RTK) surveying. Each one collects position data in a different way, so each fits a different kind of surveying and mapping job.

Static GPS uses two receivers. One stays at a known reference point, and the other is placed at the target point. It measures several satellite ranges over a long time, which can give centimeter-level...

Global Positioning System (GPS) surveying can be used to find the coordinates and elevations of park monuments. Surveyors use this method to measure precise points on Earth. In this survey, GPS receivers were used to locate two monument markers and record their height above the ground model.

The work began with mission planning. Surveyors checked satellite visibility and tried to reduce Position Dilution of Precision, or PDOP, which is a measure of how satellite geometry can affect accuracy. A...