amal 10 gps segment 123
TRANSCRIPT
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GPS SEGMENT
USERS SEGMENTDr.N.NAGAPPAN
SCIENTISTCERS
SPACE SEGMENTP.AMALADASM.ScGeoinformaticsCERS
Centre Of Excellence InRemote Sensing
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INTRODUCTION:
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History of the GPS
1969Defense Navigation Satellite
System (DNSS) formed
1973NAVSTAR Global PositioningSystem developed
1978first 4 satellites
launched
Delta rocket launch
199324th satellite launched; initial
operational capability
1995full operational capability
May 2000Military accuracy
available to all users
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GPS SEGMENT
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The first GPS segment is the space segment, which consists of 24 satellitevehicles that orbit the Earth in six orbital planes (see right)4. There are 4
equally spaced satellites per orbital plane, and the vehicles complete an orbitonce every 12 hours5. This means that there are always between 5 and 8
satellites visible anywhere on Earth at any given time6. The satellite vehiclesbroadcast radio signals that can be detected by GPS users 12,000 miles awayon Earth7. The GPS receiving units measure these digital transmissions that
arrive from the satellites to figure how far away each satellite is, and thenapply trigonometry and the concept of triangulation to pinpoint its location on
Earth8. In order to get an accurate measurement, the receiver must gathersignals from at least 4 different satellites
circularorbit s
witharadiu
sof2
6,560km
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SPACE SEGMENT
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monitor and operate the GPS satellites. There are
monitoring stations spaced around the globe and oneMaster Control Station located in Colorado Springs,
Colorado . Each station sends information to the Control
Station which then updates and corrects the navigationalmessage of the satellites. There are actually five majormonitoring systems, the figure below does not include the
Hawaiian station.
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Kwajalein Atoll
US Space Command
Control SegmentControl Segment
Hawaii
Ascension Is.Diego Garcia
Ground AntennaMaster Control Station Monitor Station
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User Segment The user requires a GPS receiver in order to receive the transmissions from the
satellites. The GPS receiver calculates the location based on signals from thesatellites. The user does not transmit anything to the satellites and therefore the
satellites don't know the user is there. The only data the satellites receive is from theMaster Control Station in Colorado. The users consist of both the military and civilians.
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One of the effects of EinsteinsSpecial Relativity theory is time
dilation.Clocks moving with high
velocity run slower then clocks
with the smaller relative velocity.Therefore, clocks in the GPS
satellites will run slower compareto the clocks on the Earthbecause GPS satellites have a
large velocity.
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Conclusions
GPS is becoming a very popular and effective tool for the precise mapping and monitoringpurpose. Many and many organizations are inducting GPS for the survey and othervarious purposes. Though, many factors affect the accuracy of the GPS survey e.g.number of satellite observed, observation time, surroundings at the place of observation,distance of each observation points etc. Accuracy also depends upon the interactedsatellites geometry. The ultimate accuracy of a GPS determined by sum of severalsources of error. The contribution of each source may vary depending on atmospheric and
equipment conditions. Precision of observation such as landslide by the GPS depends onhow above said errors can be eliminate of minimize. GPS cannot be used for theunderground mapping as site of satellite is blocked. If such sites are falls in thecontinuous mapping, GPS survey can be switchover to electronic Total Station.
GPS industry is likely to continue to develop in the civilian community besides the specificuse in defense. Now, GPS trend is continuing to be towards smaller, less expensive, andmore easily operated devices for its wider use in the many aspects of community.
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T HAN
KU
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In and Out of the Classroom
T HAN
KU