GLOBAL POSITIONING SYSTEM

IMPORTANT TERMS Azimuth - angular measurement in a circular (clockwise) direction. Azimuth - angular measurement in a circular (clockwise) direction. Coordinated Universal Time - primary time standard for the world (UTC). Coordinated Universal Time - primary time standard for the world (UTC). GPS Time - not corrected to rotation of Earth. Accurate to 19 nanoseconds (19 billionths of a second). GPS Time - not corrected to rotation of Earth. Accurate to 19 nanoseconds (19 billionths of a second). Leap Second - one second adjustment occasionally applied to UTC to compensate for the slowing of the Earth’s rotation. Leap Second - one second adjustment occasionally applied to UTC to compensate for the slowing of the Earth’s rotation. Tangent - The ratio of the opposite side of a right triangle to the adjacent side. Tangent - The ratio of the opposite side of a right triangle to the adjacent side. Triangulation - determining the location of a point by measuring angles to it from known points at either end of a fixed baseline. Triangulation - determining the location of a point by measuring angles to it from known points at either end of a fixed baseline. Trilateration - the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. Trilateration - the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles.

U.S. NAVAL OBSERVATORY Oldest scientific agency in the U.S. Oldest scientific agency in the U.S. Primary mission to produce positioning, navigation and timing for the Navy and Department of Defense. Primary mission to produce positioning, navigation and timing for the Navy and Department of Defense. Original location NW Washington D.C. Original location NW Washington D.C. Today, primary observational work done at Flagstaff Station in Arizona. Today, primary observational work done at Flagstaff Station in Arizona. Alternate Master Clock site in Colorado Springs provides precise time for GPS satellites. Alternate Master Clock site in Colorado Springs provides precise time for GPS satellites. Audible time signals transmitted in shortwave radio; 5, 10, 15 MHz. Audible time signals transmitted in shortwave radio; 5, 10, 15 MHz.

U.S. NAVAL OBSERVATORY Washington D.C.

U.S. NAVY ATOMIC CLOCKS Old Atomic Clocks at Washington D.C. New Atomic Clocks Rubidum Atomic Clock

TRIANGULATION To solve a right triangle you only need to know the measurements of two of the three sides or the 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 ◄

TRIANGULATION

FIRE TOWER OSBORN FIRE FINDER

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

GPS Satellite based global navigation satellite system, used to provide accurate location and time information anywhere on or near the Earth. Satellite based global navigation satellite system, used to provide accurate location and time information anywhere on or near the Earth. Became fully operational in Became fully operational in Built, operated and maintained by the U.S. government Built, operated and maintained by the U.S. government Can be used, freely, worldwide. Can be used, freely, worldwide. Integral part of everyday life. Integral part of everyday life.

ACCURACY & 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 BASICS Original system of 24 satellites in orbit plus a few spares and ground stations. Original system of 24 satellites in orbit plus a few spares and ground stations. Increased to 32 working satellites in 2012 to increase accuracy. Increased to 32 working satellites in 2012 to increase accuracy. Each satellite contains 2 cesium (Cs) and two rubidium (Rb) atomic clocks. Each satellite contains 2 cesium (Cs) and two rubidium (Rb) atomic clocks. Satellites are in one of six possible orbits at about 12,600 miles high. Satellites are in one of six possible orbits at about 12,600 miles high. Satellites travel at about 8,700 miles per hour. Satellites travel at about 8,700 miles per hour. There are 4 satellites per orbit. There are 4 satellites per orbit. These orbits are inclined at 55° to the equatorial plane. These orbits are inclined at 55° to the equatorial plane. ►

GPS SATELLITE SIX ORBITS

GPS BASICS (cont.) Satellites transmit information about their positions and time the information was sent. Satellites transmit information about their positions and time the information was sent. Signals received by GPS receivers. Signals received by GPS receivers. Receivers obtain accurate time from satellite/s. Receivers obtain accurate time from satellite/s. Receiver calculates distance to each satellite. Receiver calculates distance to each satellite. A fix of just latitude and longitude can be obtained from three satellites. A fix of just latitude and longitude can be obtained from three satellites. To obtain a full fix of latitude, longitude and altitude, four or more satellites are required. To obtain a full fix of latitude, longitude and altitude, four or more satellites are required. ►

MEASURING DISTANCES WITH CLOCKS Suppose we get both the satellite and the receiver to start playing the same song at the same time. Suppose we get both the satellite and the receiver to start playing the same song at the same time. Suppose we can hear both; one from the satellite and one from the receiver. Suppose we can hear both; one from the satellite and one from the receiver. The song would be out of sync. The version coming from the satellite would be a little delayed because it had to travel more than 12,600 miles. The song would be out of sync. The version coming from the satellite would be a little delayed because it had to travel more than 12,600 miles. To hear how delayed the satellite’s song is, we start delaying the receiver's version until they are both in sync. To hear how delayed the satellite’s song is, we start delaying the receiver's version until they are both in sync. The amount of time we have to shift back the receiver's version is equal to the travel time of the satellite's version. The amount of time we have to shift back the receiver's version is equal to the travel time of the satellite's version. Multiply the time by the speed of light and you get the distance to the satellite. Multiply the time by the speed of light and you get the distance to the satellite.

PSEUDO RANDOM CODE (PRC) Very complicated digital code. Very complicated digital code. Almost looks like random electrical noise. Hence the name "Pseudo-Random.“ Almost looks like random electrical noise. Hence the name "Pseudo-Random.“ Complex pattern prevents the receiver from accidentally sync up to some other signal. Complex pattern prevents the receiver from accidentally sync up to some other signal. Each satellite has its own unique Pseudo-Random Code. Guarantees that the receiver won't accidentally pick up another satellite's signal. Each satellite has its own unique Pseudo-Random Code. Guarantees that the receiver won't accidentally pick up another satellite's signal. Makes it more difficult for a hostile force to jam the system. Makes it more difficult for a hostile force to jam the system. Gives the Department of Defense a way to control access to the system. Gives the Department of Defense a way to control access to the system.

GROUND STATIONS

USES OF GPS - CIVILIAN Navigation Navigation Emergency location Emergency location Accurate time source Accurate time source Commercial vehicle location tracking Commercial vehicle location tracking Train deployment and routing Train deployment and routing Cellular telephone tracking Cellular telephone tracking On demand services location On demand services location

VEHICLE GPS & TRACKING

USES OF GPS - MILITARY Target tracking Target tracking Precision guided munitions Precision guided munitions Self-guided missiles Self-guided missiles Reconnaissance Reconnaissance Battlefield rescue Battlefield rescue Assets tracking Assets tracking Mission control Mission control

USES OF GPS - MILITARY

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