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Chapter 1: Introduction
Normally the Raystar 112 tracks up to 12 satellites (if visible) and uses
all tracked satellites for calculating position fixes. By using these
satellites, the processor can determine the amount of clock errors in
each range calculation. The receiver subtracts the error bias equally
from each range solution until the lines of position (LOP’s) intersect.
Theoretically, this process can produce highly accurate latitutde/
longitude (L/L) position fixes for navigation /- 15m (rms).
Continuous tracking of each satellite allows the receiver to perform this
timing adjustment process and to calculate accurate measurements to
the satellites. The Raystar 112 uses a 12 channel receiver. This sensor
design method provides fast efficient acquisition and accurate position
updating, even when satellites are obstructed from view.
The US Department of Defense, for security reasons, has included a
special mode in the GPS satellite system design which introduces
variable timing errors into the satellite signals. This mode is known as
“Selective Availability” (SA), and when it is enabled, is designed to
provide less accurate fixes for all users (except military users). Accuracy
in the order of +/- 100 Meters (rms) 95% of the time is obtained when
SA is ON. This means that 95% of the time the actual ship’s GPS Lat/
Long position will be within a radius of 100 meters (+/- one football field)
and 5% of the time the actual position will be out of this 100 meter circle.
Selective Availability has been enabled almost continuously since early
1991.
The use of Differential GPS technology can remove most of these
intentionally induced errors in the GPS satellite signals due to the
“Selective Availiblity” mode including errors that can result due to
environmental conditions as the satellite signals travel to earth.When
you attach Raytheon’s Differential Beacon Receiver to the Raystar 112
GPS sensor, the GPS differential corrections can improve the L/L
Summary of Contents for Raystar 112
Page 2: ...GPS SENSOR OPERATION MANUAL...
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Page 5: ...RAYSTAR 112 Installation and Operation Handbook...
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