GPS Techniques

GPS: A Tool to aid the navigator.

Definition

GPS is a satellite-based, radio navigational system. It consists of a constellation with 28 active satellites, 24 main satellites and 4 backups. Each satellite transmits data that enables the GPS receiver to provide precise position and time to the user. The GPS receivers come in several configurations: hand-held, vehicular-mounted, aircraft-mounted, and watercraft-mounted. GPS help us establish our positions on the ground, in the air, and at sea. Many receivers can receive 12 satellites at one time. GPS receivers gives us an X, Y (longitude & latitude), and Z (elevation [above sea-level]) coordinates so that we can easily mark our location on a map. Good navigation skills are still required to interpret the data that the GPS provides

Basics

GPS system has 3 of the following segments:

Space:

GPS receivers base the positions on the radio signal received from the satellites in space. The GPS receiver calculate the time difference between the signal received and the signal sent to the satellites.

Control stations:

The GPS system is controlled, checked and updated almost continuously by control stations managed by the United States Department of Defense (DoD). There are 5 monitoring control stations spread out all over the world, but there is only ONE MASTER control station, located at Schriever (formerly Falcon) Air Force Base near Colorado Spring, CO. Can you imagine how secure this place must be? There are extensive security check points, including twin razor wired-top fences and high tech detection devices.

Users:

We use GPS receivers to find positions on the ground. The GPS receiver must receive at least 3 satellites to be able to get an X & Y position and at least 4 satellites to locate an X, Y & Z position on the ground.

Capabilities

The GPS provides worldwide, 24-hour, all-weather, day or night coverage when the satellite constellation is complete. The GPS can locate the position of the user accurately to within 21 meters — 95% of the time. However, the GPS has been known to accurately locate the position of the user within 8-10 meters. It can determine the distance and direction from the user to a preprogrammed location or the distance between two programmed location called way points. It also provides exact date and time for the time zones in which the user is located.

Base Map:

Limitations

A constellation of 24 satellites broadcasts precise signals for use by navigational sets. The satellites are arranged in six rings that orbit the earth twice each day. The GPS navigational signals are similar to light rays, so anything that blocks the light will reduce or block the effectiveness of the signals. The more unobstructed the view of the sky, the better the system performs.

Compatability:

How GPS can aid the navigator