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Copy of 3D Earth Template For Later
Transcript of Copy of 3D Earth Template For Later
G. Amrutha kamal
GPS is officially know as NAVSTAR GPS-Navigational Satellite Timing And Ranging Global Positioning System .
Created and realized by department of defense- United states during 1973.
Made up of two dozen satellites working in unison, known as a satellite constellation
This constellation is currently controlled by the United States Air Force 50th Space Wing
Provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites
It costs about $750 million to manage and maintain the system per year
Mainly used for navigation, map-making and surveying.
TABLE OF CONTENTS
2) BASIC CONCEPT OF GPS
3) STRUCTURE OF GPS SYSTEM
4) GPS RECEIVER
BASIC CONCEPT OF GPS SYSTEM
A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. Each satellite continually transmits messages that include:
The time the message was transmitted and,
Satellite position at time of message transmission.
2) The receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite using the speed of light.
3) GPS receiver calculates its position using trilateration.
4) Trilateration is the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles.
STRUCTURE OF GPS SYSTEM
The total GPS configuration is comprised of three distinct segments:
1) SPACE SEGMENT:
GPS satellites fly in circular orbits at an altitude of 20,200 km and with a period of 12 hours.
Powered by solar cells, the satellites continuously orient themselves to point their solar panels toward the sun and their antenna toward the earth.
GPS TRANSMITTED SIGNALS
Two signals are transmitted on carriers:
L1 = 1575.42 MHz
L2 = 1227.60 MHz
These are derived from the system clock of
10.23 MHz (phase quadrature)
Modulation used is Direct Sequence Spread Spectrum
(code division multiple access - CDMA)
2) The Control Segment:
The Control Segment tracks the Satellites, updates
their orbiting position.
The Control Segment consists of one master control station, 5 monitor stations and 4 ground antennas distributed amongst 5 locations roughly on the earth's equator.
3) The User Segment:
Anybody that receives and uses the GPS signal.
The purpose of acquisition is to identify all satellites visible to the user.
The main function of tracking is to refine these values, keep track, and demodulate the navigation data from the specific satellite.
When the signals are properly tracked, the C/A code and the carrier wave can be removed from the signal, only leaving the navigation data bits.
The last thing to do before making position computations is to compute pseudo-ranges. The pseudo-ranges are computed based on the time of transmission from the satellite and the time of arrival at the receiver.
Military GPS user equipment has been integrated into fighters, bombers, tankers, helicopters, ships, submarines, tanks, jeeps, and soldiers' equipment.
In addition to basic navigation activities, military applications of GPS include target designation of cruise missiles and precision-guided weapons and close air support.
To prevent GPS interception by the enemy, the government controls GPS receiver exports GPS satellites also can contain nuclear detonation detectors.
Automobiles are often equipped GPS receivers - They show moving maps and information about your position on the map, speed you are traveling, buildings, highways, exits etc.
For aircraft, GPS provides - Continuous, reliable, and accurate positioning information for all phases of flight on a global basis, freely available to all.
Agriculture - Ability to work through low visibility field conditions such as rain, dust, fog and darkness increases productivity.
Disaster Relief - Deliver disaster relief to impacted areas faster, saving lives.
Marine applications - GPS allows access to fast and accurate position, course, and speed information, saving navigators time and fuel through more efficient traffic routing.