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APPENDIX C - GLOBAL POSITIONING SYSTEM (GPS)
GPS is a satellite-based global navigation system created and operated by the United States
Department of Defense (DOD). Originally intended solely to enhance military defense
capabilities, GPS capabilities have expanded to provide highly accurate position and timing
information for many civilian applications.
An in-depth GPS study is required to fully understand it, but not to see how it work or appreci-
ate what it can do for you. Simply stated, twenty-four satellites in six orbital paths circle the
earth twice each day at an inclination angle of approximately 55o to the equator. This
constellation of satellites continuously transmits coded positional and timing information at
high frequencies in the 1500-Megahertz range. GPS receivers with antennas located in a
position to clearly view the satellites, pick up these signals and use the coded information to
calculate a position in an earth coordinate system.
GPS is the navigation system of choice for today and many years to come. While GPS is
clearly the most accurate world wide all-weather navigation system yet developed, it still can
exhibit significant errors. GPS receivers determine position by calculating the time it takes for
the radio signals, transmitted from each satellite, to reach earth. It’s that old “Distance = Rate
x Time” equation. Radio waves travel at the speed of light (Rate). Time is determined, and the
fact that the satellite’s position is reported in each coded navigation message, by using a little
trigonometry the receiver can determine its location on earth.
Position accuracy depends on the receiver’s ability to accurately calculate the time it takes for
each satellite signal to travel to earth. This is where the problem lies. There are primarily
seven sources of errors that can affect the receiver’s calculation. These errors consist of:
1.
Ionosphere and troposhere delays on the radio signal.
2.
Signal multi-path.
3.
Receiver clock biases.
4.
Orbital satellite (ephemeris) position errors.
5.
GPS Satellite errors.
6.
Tracking biases (position shifts when satellites are lost and re-aquired).
7.
GPS Receiver performance and cost.
The combination of these errors and poor satellite geometry can limit GPS accuracy of a high
performance GPS Receiver to approximately 5 meters RMS and a low cost GPS Receiver to
10-15 meters RMS. Many of these errors can be reduced or eliminated through a technique
known as “Differential”.
Summary of Contents for RGL 600
Page 1: ...RGL 600 SMARTBAR SWATH PATH GUIDANCE SYSTEM OPERATION MANUAL ...
Page 2: ...Use with firmware version ____ ...
Page 66: ...61 RGL 600 MAIN UNIT CONNECTOR CABLE OPTIONS ...
Page 68: ...63 CABLE WIRING DIAGRAMS ...
Page 69: ...64 CABLE WIRING DIAGRAMS continued ...