Global Positioning SystemAnurag MishraDeputy DirectorForest Survey of India, Dehradun

Outline for TodayToday, we will review the basics of the GPS system and

Its historyKey componentsFunctioningApplications etc.

Trying to figure out where you are and where you're going is probably one of man's oldest pastimes

Latitude & Longitude780131.2 E and 302001.6 N135 745.9 W and 83724.4 S

A Little Bit of HistoryIn the past, humans had to go to pretty extreme measures to keep from getting lost.

They erected monumental landmarks, laboriously drafted detailed maps and learned to read the stars in the night sky.

For centuries, only way to navigate was to look at position of sun and stars.

Things are much easier todayStarting Rs.10,000/- you can get a pocket-sized gadget that will tell you exactly where you are on Earth at any moment. As long as you have a GPS receiver and a clear view of the sky.

Why GPS ?Accurate & Precise

Efficient, Economical

Easy to Operate

Portable

Navigation

Works Everywhere

Additional Information

Outer DescriptionInternal GPS antenna

Battery compartment

Display screen

External power & data connector

Functional keys

Primary Pages

GPS Information PageData Fields (speed, elevation and accuracy)Receiver StatusSatellite Location(sky view)Satellite signal StrengthDate & TimeCurrent Location

Satellite Location (Sky View)Satellites numbers becomes highlighted whose data is received and computed. Sky view can be oriented north or your current track towards the top of display.

Signal Strength BarIf bar is light gray : GPS accruing the data.When bar turns to black: GPS using the signal for navigation.A D in or above the bar: Indicates differential corrections are applied to the satellite.

TimelineFeasibility studies begun in 1960s

In 1978 the first experimental GPS satellites were launched

By December 1993 the GPS system achieved initial operational capability

By January 1994 a complete constellation of 24 satellites was in orbit

Contd.Full Operational Capability was declared by NAVSTAR in April 1995

The most recent launch was on 17 November 2006

The oldest GPS satellite still in operation was launched in August 1991

Background (Contd)The essential components of GPS were the 24 Navstar satellites built by Rockwell International, each the size of a large automobile.

Each of these 3,000- to 4,000-pound solar-powered satellites circles the globe at about 12,000 miles (19,300 km), making two complete rotations every day.

The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible in the sky.

Day-to-day running of GPS program and operation of system rests with the Department of Defense (DoD).

What is GPS?Satellite-based navigation system

Continuously transmits coded information

Precisely identify locations

Measuring distances from the satellites

Man-made stars

IntroductionDeveloped by US Department of Defense in 1978

24 Satellites in 6 orbits

Situated at an altitude of 20,200 km

Life of Satellite is about 7.5 to 10 years

12 hours period and orbit is precisely predictable

Contd.Satellite clock: Atomic (Rubidium, Cesium)

Powered by solar energy

There are no subscription fees or setup charges to use GPS

No restriction in using GPS signals

Doesnt work under dense canopy, covered areas

GPS works in all weather conditions

Global Positioning System (GPS)NAVSTARNAVigation Satellite Timing And Ranging satellites (NATO)

GLONASSGLObal NAvigation Satellite System (Russian)

Galileo To be operational by 2012 (EU)

NAVSTARThe only fully functional Global Navigational Satellite System

Constellation of at least 24 Medium Earth Orbit Satellites that transmit precise Microwave signals, the system enables a GPS Receiver to determine its Location, speed/direction, and time

The cost of maintaining the system is approximately US$750 million per year, including the replacement of aging satellites, and research and development

NAVSTAR

NameLaunch PeriodNumber of Satellites LaunchedCurrently in ServiceBlock I1978-1985110Block II1985-199090Block IIA1990-19971915+11Block IIR1997-20041212Block IIR-M2005-33Total5430+1

Global Navigational Satellite System (European)Known as Galileo it is to be built by the European Satellite Navigation Industries for the European Union (EU) and European Space Agency (ESA) as an alternative to the US and the Russian System

Galileo is intended to provide:

More precise measurements to all users than available through GPS or GLONASS

Global Navigational Satellite System (European)Better positioning services at high latitudes,

An independent positioning system upon which European nations can rely upon even in times of war or political disagreement.

The current project plan has the system as operational by 201112, three or four years later than originally anticipated

The Open Service (OS) will be free. An accuracy of

Global Navigation Satellite System (GLONASS) Russian GLONASS (Global'naya Navigatsionnaya Sputnikovaya Sistema)

It was developed by the former Soviet Union

Now operated for the Russian Government by the Russian Space Forces.

Development on the GLONASS began in 1976, with a goal of global coverage by 1991.

Global Navigation Satellite System (GLONASS)

Beginning in 1982, numerous satellite launches progressed the system forward until the constellation was completed in 1995.

Following completion, the system rapidly fell into disrepair with the collapse of the Russian economy.

Beginning in 2001, Russia committed to restoring the system, and in recent years has diversified and accelerated the program with a goal of restoring global coverage by 2009.

Indian Regional Navigational Satellite System (IRNSS)This is a developmental autonomous regional Satellite Navigation System being constructed and controlled by the Indian Government.

It is intended to provide an absolute position accuracy of better than 20 meters throughout India and within a region extending approximately 1,500 to 2,000 km around it.

A goal of complete Indian control has been started, with the space segment, ground segment and user receivers all being built in India.

Indian Regional Navigational Satellite System (IRNSS)

The Government approved the project in May 2006, with the intention to implement within six to seven years. The first satellite of the proposed constellation, developed at a cost of Rupees1,600 crores, is expected to be launched in 2009.

The proposed system would consist of a constellation of seven satellites and a support ground segment.

The satellites would weigh approximately 1,330 kg and their solar panels generate 1,400 watts of energy.

Beidou Navigation System (Chinese)Beidou Satellite Navigation and Positioning System is a project by China to develop an independent Satellite Navigation System.

The current Beidou-1 system (made up of 4 satellites) is experimental and has limited coverage and application.

However, China has planned to develop a truly global satellite navigation system consisting of 35 satellites (known as Compass or Beidou-2).

Beidou Navigation System (Chinese)Beidou 1A was launched on 30 October 2000, Beidou 1B followed 20 December 2000, and Beidou 2A was put into orbit on 24 May 2003.The latest Beidou navigation satellite was successfully launched on 3 February 2007

China joined the Galileo Positioning System project in September 2003 and will invest US$296 million in Galileo over the next few years

On November 2, 2006, China announced that from 2008 Beidou would offer open service with an accuracy of 10 meters.

GPS CONSTELLATION

Orbits of Different Satellites

Different Roles for SatellitesWeather satellites help meteorologists predict the weather or see what's happening at the moment. The satellites generally contain cameras that can return photos of Earth's weather.

Communications satellites allow telephone and data conversations to be relayed through the satellite. The most important feature of a communications satellite is the transponder -- a radio that receives a conversation at one frequency and then amplifies it and retransmits it back to Earth on another frequency.

Different Satellites (Contd)Broadcast satellites broadcast television signals from one point to another (similar to communications satellites).

Scientific satellites perform a variety of scientific missions. The Hubble Space Telescope is the most famous scientific satellite, but there are many others looking at everything from sun spots to gamma rays.

Navigational satellites help ships and planes navigate, e.g., GPS.

Different Satellites (Contd)Rescue satellites respond to radio distress signals. Earth observation satellites observe the planet for changes in everything from temperature to forestation to ice-sheet coverage.

Military satellites are up there, but much of the actual application information remains secret.

What does a GPS receiver do?Position and coordinates.

The distance and direction between any two waypoints

What direction you are heading

Some models can show you:how fast you are goingyour altitudea map to help you arrive at a destination

How does the GPS work?Using satellites in the sky, ground stations on earth, and a GPS receiver, the distances between each of these points can be calculated.

The distance is calculated based on the amount of time it takes for a radio signal to travel between these points.

This allows the GPS receiver to know where you are, in terms of latitude and longitude, on the earth.

TriangulationA GPS receiver's job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called triangulation or trilateration.

Triangulation in three-dimensional space can be a little tricky, so we'll start with an explanation of simple two-dimensional trilateration.

Triangulation

3D TriangulationFundamentally, three-dimensional trilateration is not much different from two-dimensional trilateration, but it's a little trickier to visualize.

Imagine the radii from the examples in the last section going off in all directions. So instead of a series of circles, you get a series of spheres.

GPS TriangulationIf you know you are 10000 miles from satellite A in the sky, you could be anywhere on the surface of a huge, imaginary sphere with a 10000-mile radius. Earth10000 miles

GPS Triangulation (Contd)If you also know you are 15000 miles from satellite B, you can overlap the first sphere with another, larger sphere. The spheres intersect in a perfect circle. 10000 miles15000 miles

GPS Triangulation (Contd)The circle intersection implies that the GPS receiver lies somewhere in a partial ring on the earth.PossibleLocations of GPS ReceiverPerfect circle formed fromlocating two satellites

GPS Triangulation (Contd)If you know the distance to a third satellite, you get a third sphere, which intersects with this circle at two points.

GPS Triangulation (Contd)The Earth itself can act as a fourth sphere -- only one of the two possible points will actually be on the surface of the planet, so you can eliminate the one in space.

Receivers generally look to four or more satellites, however, to improve accuracy and provide precise altitude information.

Calculating DistanceDistance = Speed x time

Control SegmentSpace SegmentUser SegmentThree Segments of the GPSMonitor StationsGround AntennasMaster Station

The Space SegmentArranged in the orbits in such a way that at least 4 satellites are always available

Circle earth once every 12 hours

Functions

Receive and store information from ground control segment

Maintain very accurate time

Transmit signal to the earth

Kwajalein AtollUS Space CommandThe Control SegmentHawaiiAscension Is.Diego GarciaCape Canaveral

The User Segment

Military.Search and rescue.Disaster relief.Environment, Forestry & WildlifeMarine, aeronautical and terrestrial navigation.Remote controlled vehicle and robot guidance.Satellite positioning and tracking.Shipping.Geographic Information Systems (GIS).Recreation.User Segment

GPS ReceiversBetter units have multiple receivers, so they can pick up signals from several satellites simultaneously.

Radio waves travel at the speed of light (about 186,000 miles per second, 300,000 km per second in a vacuum).

The receiver can figure out how far the signal has traveled by timing how long it took the signal to arrive.

Downloading of GPS DataData Cable

Mapsource

Pathfinder

Standard Positioning System (SPS)Provided on the GPS L1 frequency. Contains a coarse acquisition (C/A) code and a navigation data message.

The P-code and the L2 frequency is not unavailable to SPS users.

Accuracy

100 m in horizontal position 156 m in the vertical component

Precise Positioning System (PPS)Available to authorized military users and users with PPS receivers

This consists of the SPS signal plus the P code on L1 and the carrier phase measurements on L2

Accuracy

22 m in horizontal position 27 m in the vertical component

DGPS is used for higher accuracy

Differential GPS

There is no such thing as a Differential GPS

It is the Differential capability

Geodetic GPS

Differential GPSUses the point position derived from either the C/A or P-codes

Applies correction to that position.

These corrections, difference of determined position and the known position, are generated by a reference receiver, whose position is known and is fed to the instrument.

Used by the second receiver to correct its internally generated position.

True coordinates = x+0, y+0 Correction = x-5, y+3DGPS correction = x+(30-5) and y+(60+3)True coordinates = x+25, y+63Real Time Differential GPS

Causes of ErrorsIonosphere and troposphere delays

Signal multipath

Orbital errors

Number of satellites visible

Satellite geometry/shading

Intentional degradation of the satellite signal

Sources of Signal Interference

Sources of GPS ErrorStandard Positioning Service (SPS ): Civilian Users

SourceAmount of ErrorSatellite clocks:1.5 to 3.6 metersOrbital errors:< 1 meterIonosphere:5.0 to 7.0 metersTroposphere:0.5 to 0.7 metersReceiver noise:0.3 to 1.5 metersMultipath:0.6 to 1.2 metersSelective AvailabilityUser error:Up to a kilometer or more

Introduced Errors in GPSSelective Availability

To reduce horizontal positioning capabilities from approximately 20 m to 100m

Anti Spoofing

Encryption of the P-Code

Receiver Errors are Cumulative!

Ideal Satellite GeometryNSWE

Good Satellite Geometry

Poor Satellite Geometry

Planning a Navigation RouteStart= Waypoint

Applications in Forestry

Location of Plantations

Area and Perimeter

Areas

Assessment of TOF Resources

Wildlife ManagementWildlife Census, Habitats

Direct/Indirect sightings

Wildlife offenses

Settlements

Habitations & Encroachments

Forest Villages

Encroachments

Settlements inside forests

Delineation of Areas

Boundary PillarsLocation of Pillars

Bearings

Distance between pillars

Track between the pillars

Use of GPS by FSIGround truthing

Forest Inventory

Assessment of TOF

Monitoring of FDAs

Major Suppliers of GPSGarmin

Magellan

Leica

Lawrence

NaviGPS

GPS ModelsGarmin E-Trex

12 channels, 500 WP, EC, US$ 119.95

Garmin GPS 12

12 channels, 500 WP, EC, AC, WAAS, US$ 149.95

GPS ModelsGarmin GPS 76

12 channels, 500 WP, EC, AC, WAAS, US$ 219.95

Garmin GPS 76 Map

12 channels, 1000 WP, AC, EC/BM, WAAS, Map, US$ 379.95

GPS ModelsE-Trex Vista

12 channels, 1000 WP, EC, AC, WAAS, US$ 329.95

E-Trex Summit

12 channels, 500 WP, EC, Barometer, Altimeter US$ 219.95

GPS ModelsMagellan Explorist 500

14 channels,8 MB, SD card, 500 WP, EC, AC, WAAS, Map, US$ 329.95

Magellan Explorist 400

14 channels,8 MB, SD card, 500 WP, EC, AC, WAAS, Map, US$ 279.95

GPS ModelsLawrence iFinder Explorer12 channels, 500 WP, EC/BM, AC, WAAS, US$ 229.95

Lawrence iFinder H2O12 channels, 500 WP, EC, AC, WAAS, US$ 169.95

ImportantBattery Life

Size & Weight

DGPS Capability

Price

Specifications

Requirements

*****************************************************************