GLOBAL

POSITIONING

SYSTEM

IMPORTANT TERMSIMPORTANT TERMS Azimuth Azimuth - - angular measurement in a circular (clockwise) angular measurement in a circular (clockwise)

direction.direction. Coordinated Universal Time Coordinated Universal Time - - primary time standard for the primary time standard for the

world (UTC).world (UTC). GPS Time GPS Time - - not corrected to rotation of Earth. Accurate to 19 not corrected to rotation of Earth. Accurate to 19

nanoseconds (19 billionths of a second).nanoseconds (19 billionths of a second). Leap Second Leap Second -- one second adjustment occasionally applied to one second adjustment occasionally applied to

UTC to compensate for the slowing of the Earth’s rotation. UTC to compensate for the slowing of the Earth’s rotation. Tangent Tangent - - The ratio of the opposite side of a right triangle to the The ratio of the opposite side of a right triangle to the

adjacent side. adjacent side. Triangulation Triangulation - - determining the location of a point by measuring determining the location of a point by measuring

angles to it from known points at either end of a fixed baseline. angles to it from known points at either end of a fixed baseline. TrilaterationTrilateration -- the process of determining absolute or relative the process of determining absolute or relative

locations of points by measurement of distances, using the locations of points by measurement of distances, using the geometry of circles, spheres or triangles.geometry of circles, spheres or triangles.

U.S. NAVAL OBSERVATORYU.S. NAVAL OBSERVATORY Oldest scientific agency in the U.S.Oldest scientific agency in the U.S. Primary mission to produce positioning, Primary mission to produce positioning,

navigation and timing for the Navy and navigation and timing for the Navy and Department of Defense.Department of Defense.

Original location NW Washington D.C.Original location NW Washington D.C. Today, primary observational work done at Today, primary observational work done at

Flagstaff Station in Arizona.Flagstaff Station in Arizona. Alternate Master Clock site in Colorado Alternate Master Clock site in Colorado

Springs provides precise time for GPS Springs provides precise time for GPS satellites.satellites.

Audible time signals transmitted in shortwave Audible time signals transmitted in shortwave radio; 5, 10, 15 MHz. radio; 5, 10, 15 MHz.

U.S. NAVAL OBSERVATORYU.S. NAVAL OBSERVATORYWashington D.C.Washington D.C.

U.S. NAVY ATOMIC CLOCKSU.S. NAVY ATOMIC CLOCKS

Old Atomic Clocks at Washington D.C.

New Atomic Clocks

Rubidum Atomic Clock

TRIANGULATIONTRIANGULATIONTo solve a right triangle you only need to know the measurements of two of the three sides

orthe measure of one side and one of the other two angles

Tangent D X e = d

A tangent table will give you the tangent of any degree from 0 to 90 ◄

TRIANGULATIONTRIANGULATION

FIRE TOWER

OSBORN FIRE FINDER

TRILATERATIONTRILATERATIONUses geometry of circles, spheres or triangles instead of measurement of angles to determine positions

GPSGPS Satellite based global navigation Satellite based global navigation

satellite system, used to provide satellite system, used to provide accurate location and time information accurate location and time information anywhere on or near the Earth.anywhere on or near the Earth.

Became fully operational in 1994.Became fully operational in 1994. Built, operated and maintained by the Built, operated and maintained by the

U.S. governmentU.S. government Can be used, freely, worldwide.Can be used, freely, worldwide. Integral part of everyday life.Integral part of everyday life.

ACCURACY & PRECISSIONACCURACY & PRECISSION

GPS accuracy:   The accuracy refers to the degree of closeness the indicated readings are to the actual position.

GPS precision:   Is the degree to which the readings can be made. The smaller the circle of unknown the higher the precision.

GPS BASICSGPS BASICS Original system of 24 satellites in orbit plus Original system of 24 satellites in orbit plus

a few spares and ground stations.a few spares and ground stations. Increased to 32 working satellites in 2012 Increased to 32 working satellites in 2012

to increase accuracy.to increase accuracy. Each satellite contains 2 cesium (Cs) and Each satellite contains 2 cesium (Cs) and

two rubidium (Rb) atomic clocks. two rubidium (Rb) atomic clocks. Satellites are in one of six possible orbits at Satellites are in one of six possible orbits at

about 12,600 miles high.about 12,600 miles high. Satellites travel at about 8,700 miles per Satellites travel at about 8,700 miles per

hour.hour. There are 4 satellites per orbit. There are 4 satellites per orbit. These orbits are inclined at 55° to the These orbits are inclined at 55° to the

equatorial plane.equatorial plane.

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GPS SATELLITE

SIX ORBITS

GPS BASICS (cont.)GPS BASICS (cont.) Satellites transmit information about their Satellites transmit information about their

positions and time the information was sent.positions and time the information was sent. Signals received by GPS receivers.Signals received by GPS receivers. Receivers obtain accurate time from Receivers obtain accurate time from

satellite/s.satellite/s. Receiver calculates distance to each satellite.Receiver calculates distance to each satellite. A fix of just latitude and longitude can be A fix of just latitude and longitude can be

obtained from three satellites.obtained from three satellites. To obtain a full fix of latitude, longitude and To obtain a full fix of latitude, longitude and

altitude, four or more satellites are required.altitude, four or more satellites are required.

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MEASURING DISTANCES WITH CLOCKSMEASURING DISTANCES WITH CLOCKS Suppose we get both the satellite and the receiver to Suppose we get both the satellite and the receiver to

start playing the same song at the same time.start playing the same song at the same time.

Suppose we can hear both; one from the satellite and Suppose we can hear both; one from the satellite and one from the receiver. one from the receiver.

The song would be out of sync. The version coming from The song would be out of sync. The version coming from the satellite would be a little delayed because it had to the satellite would be a little delayed because it had to travel more than 12,600 miles.travel more than 12,600 miles.

To hear how delayed the satellite’s song is, we start To hear how delayed the satellite’s song is, we start delaying the receiver's version until they are both in delaying the receiver's version until they are both in sync.sync.

The amount of time we have to shift back the receiver's The amount of time we have to shift back the receiver's version is equal to the travel time of the satellite's version is equal to the travel time of the satellite's version.version.

Multiply the time by the speed of light and you get the Multiply the time by the speed of light and you get the distance to the satellite. distance to the satellite.

PSEUDO RANDOM CODE (PRC)PSEUDO RANDOM CODE (PRC) Very complicated digital code.Very complicated digital code.

Almost looks like random electrical noise. Hence the Almost looks like random electrical noise. Hence the name "Pseudo-Random.“name "Pseudo-Random.“

Complex pattern prevents the receiver from Complex pattern prevents the receiver from accidentally sync up to some other signal.accidentally sync up to some other signal.

Each satellite has its own unique Pseudo-Random Each satellite has its own unique Pseudo-Random Code. Guarantees that the receiver won't accidentally Code. Guarantees that the receiver won't accidentally pick up another satellite's signal.pick up another satellite's signal.

Makes it more difficult for a hostile force to jam the Makes it more difficult for a hostile force to jam the system.system.

Gives the Department of Defense a way to control Gives the Department of Defense a way to control access to the system. access to the system.

GROUND STATIONSGROUND STATIONS

USES OF GPS - CIVILIANUSES OF GPS - CIVILIAN NavigationNavigation Emergency locationEmergency location Accurate time sourceAccurate time source Commercial vehicle location trackingCommercial vehicle location tracking Train deployment and routingTrain deployment and routing Cellular telephone trackingCellular telephone tracking On demand services location On demand services location

VEHICLE GPS & TRACKINGVEHICLE GPS & TRACKING

USES OF GPS - MILITARYUSES OF GPS - MILITARY Target trackingTarget tracking Precision guided munitionsPrecision guided munitions Self-guided missilesSelf-guided missiles ReconnaissanceReconnaissance Battlefield rescueBattlefield rescue Assets trackingAssets tracking Mission controlMission control

USES OF GPS - MILITARYUSES OF GPS - MILITARY

USES OF GPS - MILITARYUSES OF GPS - MILITARY

QUESTIONS ?