Gps
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Remote sensing and GIS are useful tools for civil engineering projects. The Global Positioning System (GPS) uses 24 satellites that orbit the earth to provide location and time information to GPS receivers. It has three segments: space (satellites), control (monitoring stations), and user (receivers). GPS works by precisely measuring the time it takes signals from multiple satellites to reach a receiver, allowing the device to triangulate its position. Its applications include navigation, mapping, precision agriculture, and more. Other global satellite systems include GLONASS, Galileo, BeiDou, and future systems like Compass.
Gps
- 1. APPLICATION OF REMOTE SENSING AND GEOGRAPHICAL INFORMATION SYSTEM IN CIVIL ENGINEERING Date: INSTRUCTORS DR. MOHSIN SIDDIQUE ASSIST. PROFESSOR DEPARTMENT OF CIVIL ENGINEERING
- 2. Official name of GPS is NAVigational Satellite Timing And Ranging Global Positioning System (NAVSTAR GPS) Global Positioning Systems (GPS) is a form of Global Navigation Satellite System (GNSS) Only completely functional one of its kind at this time First developed by the United States Department of Defense Consists of two dozen GPS satellites in medium Earth orbit (The region of space between 2000km and 35,786 km) Global Positioning System (GPS) 2
- 3. First GPS satellite launched in 1978 Full constellation achieved in 1994 Satellites built to last about 10 years Approximately 2,000 pounds,17 feet across Transmitter power is only 50 watts or less X,Y,Z and t data streams sent continuously from SVs L1 channel: civil use L2 channel: military / special licensees only GPS Satellites (Satellite Vehicles(SVs)) 3
- 4. 24+ satellites 6 planes with 55°inclination Each plane has 4-5 satellites Broadcasting position and time info on 2 frequencies Constellation has spares Very high orbit 20,200 km 1 revolution in approximately 12 hrs Travel approx. 7,000mph Considerations Accuracy Survivability Coverage Space Segment 4
- 5. Global Positioning System (GPS) It consists of Three Segments: User Segment Control Segment Space Segment 5
- 6. The Control Segment consists of 3 entities: Master Control System Monitor Stations Ground Antennas Master Control System The master control station, located at Falcon Air Force Base in Colorado Springs, Colorado, is responsible for overall management of the remote monitoring and transmission sites. GPS ephemeris is the tabulation of computed positions, velocities and derived right ascension and declination of GPS satellites at specific times for eventual upload to GPS satellites. Control Segment 6
- 7. Monitor Stations Six monitor stations are located at Falcon Air Force Base in Colorado, Cape Canaveral, Florida, Hawaii, Ascension Island in the Atlantic Ocean, Diego Garcia Atoll in the Indian Ocean, and Kwajalein Island in the South Pacific Ocean. Each of the monitor stations checks the exact altitude, position, speed, and overall health of the orbiting satellites. The control segment uses measurements collected by the monitor stations to predict the behavior of each satellite's orbit and clock. The prediction data is up-linked, or transmitted, to the satellites for transmission back to the users. The control segment also ensures that the GPS satellite orbits and clocks remain within acceptable limits. A station can track up to 11 satellites at a time. Control Segment 7
- 8. This "check-up" is performed twice a day, by each station, as the satellites complete their journeys around the earth. Variations such as those caused by the gravity of the moon, sun and the pressure of solar radiation, are passed along to the master control station. Ground antennas Ground antennas monitor and track the satellites from horizon to horizon. They also transmit correction information to individual satellites. Control Segment 8
- 9. Control Segment 9 Master Control Station Monitor Station Ground Antenna Colorado Springs Hawaii Ascension Islands Diego Garcia Kwajalein Monitor and Control 9
- 10. Control Segment: Maintaining the System (5) Monitor Stations Correct Orbit and clock errors Create new navigation message Observe ephemeris and clock Falcon AFB Upload Station 10
- 11. The user's GPS receiver is the US of the GPS system. GPS receivers are generally composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly- stable clock, commonly a crystal oscillator). They can also include a display for showing location and speed information to the user. A receiver is often described by its number of channels this signifies how many satellites it can monitor simultaneously. As of recent, receivers usually have between twelve and twenty channels. Using the RTCM SC-104 format, GPS receivers may include an input for differential corrections. This is typically in the form of a RS-232 port at 4,800 bps speed. Data is actually sent at a much lower rate, which limits the accuracy of the signal sent using RTCM. Receivers with internal DGPS receivers are able to outclass those using external RTCM data. User Segment 11 The Radio Technical Commission for Maritime Services (RTCM)
- 12. Land, Sea and Air Navigation and Tracking Surveying/ Mapping Military Applications Recreational Uses Common Uses for GPS 12
- 13. How GPS Works Space Segment 24+ Satellites The Current Ephemeris is Transmitted to Users Monitor Stations Diego Garcia Ascension Island Kwajalein Hawaii Colorado SpringsThis image cannot currently be displayed. GPS Control Colorado Springs End User 13
- 14. Triangulation/Trilateration 14 Satellite 1 Satellite 2 Satellite 3 Satellite 4
- 15. How GPS Works A visual example of the GPS constellation in motion with the Earth rotating. Notice how the number of satellites in view from a given point on the Earth's surface, in this example at 45°N, changes with time.
- 16. GPS satellites broadcast three different types of data in the primary navigation signal. Almanac – sends time and status information about the satellites. Ephemeris – has orbital information that allows the receiver to calculate the position of the satellite. This data is included in the 37,500 bit Navigation Message, which takes 12.5 minutes to send at 50 bps. Satellites broadcast two forms of clock information Coarse / Acquisition code (C/A) - freely available to the public. The C/A code is a 1,023 bit long pseudo-random code broadcast at 1.023 MHz, repeating every millisecond. Restricted Precise code (P-code) - reserved for military usage. The P-code is a similar code broadcast at 10.23 MHz, but it repeats only once a week. In normal operation, the anti-spoofing mode, the P code is first encrypted into the Y-code, or P(Y), which can only be decrypted by users a valid key. How GPS Works 16
- 17. GPS Frequencies L1 (1575.42 MHz) - Mix of Navigation Message, coarse-acquisition (C/A) code and encrypted precision P(Y) code. L2 (1227.60 MHz) - P(Y) code, plus the new L2C code on the Block IIR-M and newer satellites. L3 (1381.05 MHz) - Used by the Defense Support Program to signal detection of missile launches, nuclear detonations, and other applications. L4 (1379.913 MHz) - Being studied for additional correction to the part of the atmosphere that is ionized by solar radiation. L5 (1176.45 MHz) – To be used as a civilian safety-of-life (SoL) signal. Internationally protected range for aeronautical navigation. The first satellite that using this signal to be launched in 2008. How GPS Works 17
- 18. Position Calculations The coordinates are calculated according to the World Geodetic System WGS84 coordinate system. The satellites are equipped with atomic clocks Receiver uses an internal crystal oscillator-based clock that is continually updated using the signals from the satellites. Receiver identifies each satellite's signal by its distinct C/A code pattern, then measures the time delay for each satellite. The receiver emits an identical C/A sequence using the same seed number the satellite used. By aligning the two sequences, the receiver can measure the delay and calculate the distance to the satellite, called the pseudorange. How GPS Works 18
- 19. Orbital position data from the Navigation Message is used to calculate the satellite's precise position. Knowing the position and the distance of a satellite indicates that the receiver is located somewhere on the surface of an imaginary sphere centered on that satellite and whose radius is the distance to it. When four satellites are measured at the same time, the point where the four imaginary spheres meet is recorded as the location of the receiver. Earth-based users can substitute the sphere of the planet for one satellite by using their altitude. Often, these spheres will overlap slightly instead of meeting at one point, so the receiver will yield a mathematically most- probable position. How GPS Works 19
- 20. Accuracy The nearness of a measurement to the standard or true value Precision The degree to which several measurements provide answers very close to each other. Accuracy and Precision 20
- 21. Selective Availability Intentional degradation of GPS accuracy 100m in horizontal and 160m in vertical Accounted for most error in standard GPS Turned off May 2, 2000 Geometric Dilution of Precision (GDOP) Describes sensitivity of receiver to changes in the geometric positioning of the SVs The higher the DOP value, the poorer the measurement Sources of Error 21
- 22. Clock Error Differences between satellite clock and receiver clock Ionosphere Delays Delay of GPS signals as they pass through the layer of charged ions and free electrons known as the ionosphere. Multipath Error Caused by local reflections of the GPS signal that mix with the desired signal Sources of Error 22 GPS Antenna Hard Surface Satellite 22
- 23. 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. Civil GPS uses 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. Some of the market leaders in this technology are Garmin and TomTom, not to mention the built in GPS navigational systems from automotive manufacturers. Applications of GPS 23
- 24. For aircraft, GPS provides Continuous, reliable, and accurate positioning information for all phases of flight on a global basis, freely available to all. Safe, flexible, and fuel-efficient routes for airspace service providers and airspace users. Potential decommissioning and reduction of expensive ground based navigation facilities, systems, and services. Increased safety for surface movement operations made possible by situational awareness. Agriculture GPS provides precision soil sampling, data collection, and data analysis, enable localized variation of chemical applications and planting density to suit specific areas of the field. Ability to work through low visibility field conditions such as rain, dust, fog and darkness increases productivity. Accurately monitored yield data enables future site-specific field preparation. Applications of GPS 24
- 25. Disaster Relief Deliver disaster relief to impacted areas faster, saving lives. Provide position information for mapping of disaster regions where little or no mapping information is available. Example, using the precise position information provided by GPS, scientists can study how strain builds up slowly over time in an attempt to characterize and possibly anticipate earthquakes in the future. Marine applications GPS allows access to fast and accurate position, course, and speed information, saving navigators time and fuel through more efficient traffic routing. Provides precise navigation information to boaters. Enhances efficiency and economy for container management in port facilities. Applications of GPS
- 26. Other Applications not mentioned here include Railroad systems Recreational activities (returning to the same fishing spot) Heading information – replacing compasses now that the poles are shifting Weather Prediction Skydiving – taking into account winds, plane and dropzone location Many more! Applications of GPS 26
- 27. Other satellite navigation systems in use or various states of development include: GLONASS – Глобальная Навигационная Спутниковая Система), acronym for Globalnaya Navigatsionnaya Sputnikovaya Sistema or Global Navigation Satellite System, Russia's global navigation system. Fully operational worldwide. Galileo – a global system being developed by the European Union and other partner countries, planned to be operational by 2014 Beidou – People's Republic of China's regional system, currently limited to Asia and the West Pacific COMPASS – People's Republic of China's global system, planned to be operational by 2020 IRNSS – India's regional navigation system, planned to be operational by 2012, covering India and Northern Indian Ocean QZSS – Quasi-Zenith Satellite System, Japanese regional system covering Asia and Oceania Other satellite navigation systems
- 28. Other satellite navigation systems Comparison of GPS, GLONASS, Galileo and Compass (medium earth orbit) satellite navigation system orbits with the International Space Station, Hubble Space Telescope and Iridium constellation orbits, Geostationary Earth Orbit, and the nominal size of the Earth. The Moon's orbit is 9.1 times larger (in radius and length) than geostationary orbit.
- 29. Comments…. Questions…. Suggestions…. 29 I am greatly thankful to all the information sources (regarding remote sensing and GIS) on internet that I accessed and utilized for the preparation of present lecture. Thank you !