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Global Positioning System (GPS) technology is changing the way we work and play. You can use GPS technology when you are driving, flying,
fishing, sailing, hiking, running, biking, working, or exploring. With a GPS receiver, you have an amazing amount of information at your
fingertips. Here are just a few examples of how you can use GPS technology.
•
Know precisely how far you have run and at what pace while tracking your path so you can find your way home
•
Pinpoint the perfect fishing spot on the water and easily relocate it
•
Get the closest location of your favorite restaurant when you are out-of-town
•
Find the nearest airport or identify the type of airspace in which you are flying
The Global Positioning System (GPS) is a satellite-based navigation system that sends and receives radio signals. A GPS receiver acquires these
signals and provides you with information. Using GPS technology, you can determine location, velocity, and time, 24 hours a day, in any
weather conditions anywhere in the world—for free.
GPS, formally known as the NAVSTAR (Navigation Satellite Timing and Ranging)
Global Positioning System, originally was developed for the military. Because of its
popular navigation capabilities and because you can access GPS technology using small,
inexpensive equipment, the government made the system available for civilian use. The
USA owns GPS technology and the Department of Defense maintains it.
GPS technology requires the following three segments:
•
Space segment
(Page
4)
•
Control segment
(Page
4)
•
User segment
(Page
5)
Space.Segment
At least 24 GPS satellites orbit the earth twice a day in a specific pattern. They travel at
approximately 7,000 miles per hour about 12,000 miles above the earth's surface. These
satellites are spaced so that a GPS receiver anywhere in the world can receive signals
from at least four of them.
Each GPS satellite constantly sends coded radio signals (known as pseudorandom code)
to the earth. These GPS satellite signals contain the following information:
•
The particular satellite that is sending the information
•
Where that satellite should be at any given time (the precise location of the satellite is
called ephemeris data)
•
Whether or not the satellite is working properly
•
The date and time that the satellite sent the signal
The signals can pass through clouds, glass, and plastic. Most solid objects such as buildings attenuate (decrease the power of) the signals. The
signals cannot pass through objects that contain a lot of metal or objects that contain water (such as underwater locations).
The GPS satellites are powered by solar energy. If solar energy is unavailable, for example, when the satellite is in the earth's shadow, the
satellites use backup batteries to continue running. Each GPS satellite is built to last about 10 years. The Department of Defense monitors and
replaces the satellites to ensure that GPS technology continues to run smoothly for years to come.
Control.Segment
The control segment is responsible for constantly monitoring satellite health, signal integrity, and orbital configuration from the ground. The
control segment includes the following sections:
4
4
Introduction
What.is.GPS?
GPS Beginner's Guide
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