APPLICATION OF REMOTE SENSING AND

GEOGRAPHICAL INFORMATION SYSTEM IN

CIVIL ENGINEERING

Date:

INSTRUCTORS

DR. MOHSIN SIDDIQUE

ASSIST. PROFESSOR

DEPARTMENT OF CIVIL ENGINEERING

� Official name of GPS isNAVigational Satellite Timing AndRanging Global Positioning System(NAVSTAR GPS)

� Global Positioning Systems (GPS) isa form of Global NavigationSatellite System (GNSS)

� Only completely functional oneof its kind at this time

� First developed by the United StatesDepartment 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

� 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

� 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 Segment4

Global Positioning System (GPS)

It consists of Three Segments:�User Segment�Control Segment�Space Segment

5

� 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 ColoradoSprings, Colorado, is responsible for overall management of the remotemonitoring and transmission sites.

� GPS ephemeris is the tabulation of computed positions, velocities and derivedright ascension and declination of GPS satellites at specific times for eventualupload to GPS satellites.

Control Segment6

� Monitor Stations

� Six monitor stations are located at Falcon Air Force Base in Colorado, CapeCanaveral, Florida, Hawaii, Ascension Island in the Atlantic Ocean, DiegoGarcia Atoll in the Indian Ocean, and Kwajalein Island in the South PacificOcean.

� Each of the monitor stations checks the exact altitude, position, speed, andoverall health of the orbiting satellites.

� The control segment uses measurements collected by the monitor stations topredict the behavior of each satellite's orbit and clock.

� The prediction data is up-linked, or transmitted, to the satellites fortransmission back to the users.

� The control segment also ensures that the GPS satellite orbits and clocksremain within acceptable limits. A station can track up to 11 satellites at atime.

Control Segment7

� 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 Segment8

Control Segment

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Master Control Station

Monitor Station

Ground Antenna

Colorado

Springs

Hawaii Ascension

Islands

Diego

Garcia

Kwajalein

Monitor and Control

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Control Segment: Maintaining the System

(5) Monitor Stations

Correct Orbitand clock

errorsCreate new

navigation message

Observeephemerisand clock

Falcon AFBUpload Station

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� The user's GPS receiver is the US of the GPS system.

� GPS receivers are generally composed of an antenna, tuned to thefrequencies 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 tothe user.

� A receiver is often described by its number of channels this signifies how manysatellites it can monitor simultaneously. As of recent, receivers usually havebetween twelve and twenty channels.

� Using the RTCM SC-104 format, GPS receivers may include an input fordifferential corrections.

� This is typically in the form of a RS-232 port at 4,800 bps speed. Data isactually sent at a much lower rate, which limits the accuracy of the signalsent using RTCM.

� Receivers with internal DGPS receivers are able to outclass those usingexternal RTCM data.

User Segment11

The Radio Technical Commission for

Maritime Services (RTCM)

� Land, Sea and Air Navigation and Tracking

� Surveying/ Mapping

� Military Applications

� Recreational Uses

Common Uses for GPS12

How GPS Works

Space Segment24+ Satellites

The Current Ephemeris is

Transmitted to Users

Monitor Stations

Diego GarciaAscension Island

Kwajalein Hawaii

Colorado SpringsThis image cannot currently be displayed.

GPS Control Colorado Springs

End User

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Triangulation/Trilateration14

Satellite 1 Satellite 2

Satellite 3Satellite 4

How GPS Works

A visual example of the GPS constellation in motion with theEarth rotating. Notice how the number of satellites in view froma given point on the Earth's surface, in this example at 45°N,changes with time.

� GPS satellites broadcast three different types of data in the primarynavigation signal.

� Almanac – sends time and status information about the satellites.

� Ephemeris – has orbital information that allows the receiver to calculatethe position of the satellite.

� This data is included in the 37,500 bit Navigation Message, which takes12.5 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/Acode 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-codeis a similar code broadcast at 10.23 MHz, but it repeats only once aweek. In normal operation, the anti-spoofing mode, the P code is firstencrypted into the Y-code, or P(Y), which can only be decrypted by users avalid key.

How GPS Works 16

� 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 andnewer satellites.

� L3 (1381.05 MHz) - Used by the Defense Support Program to signaldetection of missile launches, nuclear detonations, and other applications.

� L4 (1379.913 MHz) - Being studied for additional correction to the part ofthe 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

� Position Calculations

� The coordinates are calculated according to the World Geodetic SystemWGS84 coordinate system.

� The satellites are equipped with atomic clocks

� Receiver uses an internal crystal oscillator-based clock that is continuallyupdated using the signals from the satellites.

� Receiver identifies each satellite's signal by its distinct C/A code pattern, thenmeasures the time delay for each satellite.

� The receiver emits an identical C/A sequence using the same seed number thesatellite used.

� By aligning the two sequences, the receiver can measure the delay andcalculate the distance to the satellite, called the pseudorange.

How GPS Works 18

� Orbital position data from the Navigation Message is used to calculate thesatellite's precise position. Knowing the position and the distance of a satelliteindicates that the receiver is located somewhere on the surface of animaginary sphere centered on that satellite and whose radius is the distanceto it.

� When four satellites are measured at the same time, the point where the fourimaginary spheres meet is recorded as the location of the receiver.

� Earth-based users can substitute the sphere of the planet for one satellite byusing their altitude. Often, these spheres will overlap slightly instead ofmeeting at one point, so the receiver will yield a mathematically most-probable position.

How GPS Works 19

� 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 Precision20

� 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 Error21

� 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

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GPS

Antenna

Hard Surface

Satellite

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� 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 GPS23

� 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 GPS24

� 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

� 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 GPS26

� 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

Other satellite navigation systems

Comparisonof GPS, GLONASS, Galileo and

Compass (medium earth

orbit) satellite navigationsystem orbits with the International

Space Station, Hubble Space

Telescope and Iridium

constellation orbits, GeostationaryEarth Orbit, and the nominal size of

the Earth.

The Moon's orbit is 9.1 times larger

(in radius and length) than

geostationary orbit.

Comments….

Questions….

Suggestions….

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I am greatly thankful to all the information sources(regarding remote sensing and GIS) on internet that Iaccessed and utilized for the preparation of presentlecture.

Thank you !