WHAT IS G.P.S.
The global positioning system(GPS) is a satellite-based navigation system made up of at least 24 satellite. Gps works in any weather conditions, anywhere in the world24 hours in a day, with no subscription fees or set up costs. Gps is used for navigation in-plane ships cars and trucks also. The system gives critical abilities to military and civilian users around the globe. Gps provide continuous real-time 3-dimensional positioning, navigation and timing worldwide. Us department of defence (DSDOD) originally put the satellites into orbit for military use, but they were made available for civilian use in the 1980s.
History OF Gps.:-
The Gps project was launched in the US in 1973 to overcome the limitations of previous navigation systems in 1973 to overcome the limitations of previous navigation systems. Integrating ideas from several predecessors, including classified engineering design studies from the 1960s. The US Department of Defence developed the system which uses 24 satellites .it was initially developed for use by the US military and became fully operational in1995. It was available for civilian from the 1980s. The work of Gladys West is credited as instrumental in the development of computational techniques for detecting satellite position with the precision needed for Gps.
The design of Gps is based partly on similar ground-level radio navigation systems such as CORAN and the DECCA NAVIGATOR, developed in the early 1940s.
GPS satellite circles the earth twice a day in a precise orbit. each satellite transmits a unique signal and orbit parameters that allow GPS devices to decode and compute the precise location of the satellite.GPS satellite transmits a radio signal which contains two information
1.time &
2. location.
there are two types of time
1.sent time
2. receive time.
Since the speed of radio wave is constant and independent of the satellite speed, the time delay between sent and receive time is proportional to the distance from the satellite and the receiver.
The receiver uses a minimum of 3 satellite to determine the precise location. In the diagram, at first, the receiver receives the data from satelliteA. now the receiver may be anywhere of SAT A
coverage area, shown as the circle in the diagram. Now the receiver receives the same data from SAT B and SAT C . Where the coverage area of A, B, C co-inside, that is the accurate location of the receiver. The receiver also uses the 4th satellite to determine the exact time of the receiver.
1.space segment;the GPS satellites
2. The control system; operated by the US military
3. The user segment; which includes both military and civilian uses and their GPS equipment.
SPACE SEGMENT:- The space segment is the number of satellites in the constellation. It comprises of 33 satellites circling the earth every 12 hours at 12,000 miles in altitude. The function of the space segment is utilized to route/navigation signals and to store and retransmit the route/navigation message sent by the control segment. These transmissions are controlled by highly stable atomic clocks on the satellites to ensure that the users will have at least 4 simultaneous satellites in view from any point at the earth surface at any time.
CONTROL SEGMENT:- The control segment comprises of the master control station and five monitor stations outfitted with an atomic clock that is spread around the globe. The five monitor stations monitor the GPS satellite system and then send the qualified information to the master control station where abnormalities are revised and sent back to the GPS satellite through ground antennas.
USER SEGMENT:- The user segment comprises of GPS receiver, which receives the signals from the GPS satellites and determines how far away it is from each satellite. Mainly this segment is used for US military, missile guidance, civilian applied for GPS in almost every field. Most of the civilian use this from survey to transportation to natural resources and from there agriculture purpose and mapping too.
Today's Gps receivers are extremely accurate, thanks to their parallel multi-channel design. Our receivers are quick to lock onto satellites when first turned on. They maintain a tracking lock in dense tree cover or in urban settings with tall buildings. Certain atmospheric factors and other error sources can affect the accuracy of GPS. Garmin GPS receivers are typically accurate to within 10 meters. Accuracy is even better on the water.
Some Gramin GPS receiver accuracy is improved with WAAS ( wide-area augmentation system).
This capability can improve accuracy to better than 3 meters, by providing correction to the atmosphere. Users can also get better accuracy with differential GPS (DGPS), which corrects GPS distance to within an average of 1 to 3 meters. The US COAST GUARD operates the most common DGPS services, consisting of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters.
ASTRONOMY:-Both positional and clock synchronization data is used in astronomy and celestial mechanisms. GPS is also used in both amateur astronomy with a small telescope as well as by professional observators for finding extrasolar planets.
AUTOMATED VEHICLE: - Applying location and routes for cars and trucks to function without a human driver.
CARTOGRAPHY:- Both civilian and military cartographers use GPS extensively.
CELLULAR TELEPHONY:- Clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/ CELLar position detection for mobile emergency calls and other applications.
DISASTER RELIEF/ EMERGENCY SERVICES:- Many emergency services depend upon GPS for location and timing capabilities.
GPS EQUIPPED RADIO SONDES AND DROPSONDES:- Measure and calculate the atmospheric pressure, wind speed and direction up to 27 km from earth's surface.
GEOFANCING:- Vehicle tracking systems, person tracking systems, and pet tracking systems use GPS to locate devices that are attached to carried by a person, vehicle, or pet. The application can provide continuous designated area.
GEOTAGGING:- Applies location coordinates to digital objects such as photographs and other documents for the purpose such as creating map overlays with devices like Nikon GP -1.
NAVIGATION:- Navigators value digitally precise velocity and orientation measurements.
ROBOTICS:- self-navigating, autonomous robots using a GPS sensor, which calculate altitude, longitude, time, speed and heading.
SURVEYING:- surveyors use absolute locations to make maps and determine property boundaries.
1.GPS satellite-based navigation system is an important tool for military, civil and commercial uses.
2. Vehicle tracking systems GPS based navigation systems can provide us with turn by turn directions.
3.Very high speed of location tracking.
1. Gps satellite signal is too weak compared to phone signals so it does not work as well indoors, under trees etc.
2. The highest accuracy requires line-of-sight from the receiver to the satellite, this is why GPS does not work very well in the urban environment
There are other systems to GPS in the world which are all classified as the GLOBAL NAVIGATION SATELLITE SYSTEM( GNSS).GLONASS is a satellite system created by
Russia. The European space agency is creating Galileo, while China is creating BEIDOU. India has already designed its own navigation system NAVIC which is now limited within India's coastal regions, but we can expect it will be a fully functional navigation system in a few years.
BASIC CONCEPTS:-
The GPS is based on time and the known position of GPS specialized satellites. The satellites carry very stable atomic clock that is synchronized with one another and with the ground clocks. no drift from true time maintained on the ground is corrected daily. In the same manner, the satellite locations are known with great precision. Gps receivers have clocks as well, but they are not as stabilized as the satellite.GPS satellite circles the earth twice a day in a precise orbit. each satellite transmits a unique signal and orbit parameters that allow GPS devices to decode and compute the precise location of the satellite.GPS satellite transmits a radio signal which contains two information
1.time &
2. location.
there are two types of time
1.sent time
2. receive time.
Since the speed of radio wave is constant and independent of the satellite speed, the time delay between sent and receive time is proportional to the distance from the satellite and the receiver.
The receiver uses a minimum of 3 satellite to determine the precise location. In the diagram, at first, the receiver receives the data from satelliteA. now the receiver may be anywhere of SAT A
coverage area, shown as the circle in the diagram. Now the receiver receives the same data from SAT B and SAT C . Where the coverage area of A, B, C co-inside, that is the accurate location of the receiver. The receiver also uses the 4th satellite to determine the exact time of the receiver.
SEGMENTS OF GPS:-
The GPS system consists of three segments1.space segment;the GPS satellites
2. The control system; operated by the US military
3. The user segment; which includes both military and civilian uses and their GPS equipment.
SPACE SEGMENT:- The space segment is the number of satellites in the constellation. It comprises of 33 satellites circling the earth every 12 hours at 12,000 miles in altitude. The function of the space segment is utilized to route/navigation signals and to store and retransmit the route/navigation message sent by the control segment. These transmissions are controlled by highly stable atomic clocks on the satellites to ensure that the users will have at least 4 simultaneous satellites in view from any point at the earth surface at any time.
CONTROL SEGMENT:- The control segment comprises of the master control station and five monitor stations outfitted with an atomic clock that is spread around the globe. The five monitor stations monitor the GPS satellite system and then send the qualified information to the master control station where abnormalities are revised and sent back to the GPS satellite through ground antennas.
USER SEGMENT:- The user segment comprises of GPS receiver, which receives the signals from the GPS satellites and determines how far away it is from each satellite. Mainly this segment is used for US military, missile guidance, civilian applied for GPS in almost every field. Most of the civilian use this from survey to transportation to natural resources and from there agriculture purpose and mapping too.
HOW ACCURATE IS GPS?
Today's Gps receivers are extremely accurate, thanks to their parallel multi-channel design. Our receivers are quick to lock onto satellites when first turned on. They maintain a tracking lock in dense tree cover or in urban settings with tall buildings. Certain atmospheric factors and other error sources can affect the accuracy of GPS. Garmin GPS receivers are typically accurate to within 10 meters. Accuracy is even better on the water.
Some Gramin GPS receiver accuracy is improved with WAAS ( wide-area augmentation system).
This capability can improve accuracy to better than 3 meters, by providing correction to the atmosphere. Users can also get better accuracy with differential GPS (DGPS), which corrects GPS distance to within an average of 1 to 3 meters. The US COAST GUARD operates the most common DGPS services, consisting of a network of towers that receive GPS signals and transmit a corrected signal by beacon transmitters.
USE OF GPS.
ASTRONOMY:-Both positional and clock synchronization data is used in astronomy and celestial mechanisms. GPS is also used in both amateur astronomy with a small telescope as well as by professional observators for finding extrasolar planets.
AUTOMATED VEHICLE: - Applying location and routes for cars and trucks to function without a human driver.
CARTOGRAPHY:- Both civilian and military cartographers use GPS extensively.
CELLULAR TELEPHONY:- Clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/ CELLar position detection for mobile emergency calls and other applications.
DISASTER RELIEF/ EMERGENCY SERVICES:- Many emergency services depend upon GPS for location and timing capabilities.
GPS EQUIPPED RADIO SONDES AND DROPSONDES:- Measure and calculate the atmospheric pressure, wind speed and direction up to 27 km from earth's surface.
GEOFANCING:- Vehicle tracking systems, person tracking systems, and pet tracking systems use GPS to locate devices that are attached to carried by a person, vehicle, or pet. The application can provide continuous designated area.
GEOTAGGING:- Applies location coordinates to digital objects such as photographs and other documents for the purpose such as creating map overlays with devices like Nikon GP -1.
NAVIGATION:- Navigators value digitally precise velocity and orientation measurements.
ROBOTICS:- self-navigating, autonomous robots using a GPS sensor, which calculate altitude, longitude, time, speed and heading.
SURVEYING:- surveyors use absolute locations to make maps and determine property boundaries.
ADVANTAGES OF GPS:-
1.GPS satellite-based navigation system is an important tool for military, civil and commercial uses.
2. Vehicle tracking systems GPS based navigation systems can provide us with turn by turn directions.
3.Very high speed of location tracking.
DISADVANTAGES OF GPS:-
1. Gps satellite signal is too weak compared to phone signals so it does not work as well indoors, under trees etc.
2. The highest accuracy requires line-of-sight from the receiver to the satellite, this is why GPS does not work very well in the urban environment
GPS SI ERROR SOURCES:-
Factors can affect GPS signal and accuracy include the followings.
IONOSPHERE AND TROPOSPHERE DELAYS:- Satellites signals slows when they pass through the atmosphere. The GPS system uses a built-in model to partially correct for this type of error
SIGNAL MULTIPATH:- The GPS signal may reflect off objects such as tall buildings or large rock surfaces before it reaches the receiver, which increases the travel time of the signal and causes errors.
RECEIVER CLOCK ERROR:- A receiver's built-in clock may have slightly timing errors because it is less accurate than the atomic clock on the GPS satellites.
ORBITAL ERRORS:- The satellites reported location may not be accurate.
NUMBER OF SATELLITE VISIBLE:- The more satellites GPS receiver can "see" the better accuracy it will gain. When a signal is blocked you may gate position errors or possibly no location
SATELLITE GEOMETRY/ SHADING:- Satellite signals are more effective when satellites are located at wide angles relative to each other, rather than in a line or tight grouping.
OTHR GPS SYSTEM:-
There are other systems to GPS in the world which are all classified as the GLOBAL NAVIGATION SATELLITE SYSTEM( GNSS).GLONASS is a satellite system created by
Russia. The European space agency is creating Galileo, while China is creating BEIDOU. India has already designed its own navigation system NAVIC which is now limited within India's coastal regions, but we can expect it will be a fully functional navigation system in a few years.
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