GPS

What is GPS? GPS is a space based all weather radio navigation system.

GPS Provides Position (geographic), Velocity & Time (PVT) Quickly, Economically And Precisely 24 hours a day, anywhere in the world under the sky

Components of GPS Space segment Control segment User segment

Salient steps The receiver picks up the signals from the satellites; Uses signal travel time to calculate distance to the satellites Using Analytical Principle, position of the receiver gets calculated.

Space segment 24 satellites Orbit every 12 hours at 20,200 kms 4 satellites in each of 6 orbital planes Transmit a uniquely coded radio signal Equipped with onboard atomic standard

What is so special about an 20200 km orbit? ‘ Orbits’ twice per day Large ‘viewable’ area

Positioning With Satellite Satellites are reference points to locations on earth (their location are known) A location of a point on earth is identified by “triangulation” Travel time of each signal is determined Signals travel at Speed of light Distance = Travel Time * Speed of Light

Principle of working using GPS The basis of GPS technology is precise measurement of time; Use of orbiting satellite position to find location of receiver by method of resection

S 1 (x 1 ,y 1 ,z 1 ) S 2 (x 2 ,y 2 ,z 2 ) S 3 (x 3 ,y 3 ,z 3 ) S 4 (x 4 ,y 4 ,z 4 ) GPS Receiver  1 =  {(x 1 -x) 2 +(y 1 -y) 2 +(z 1 -z) 2 } + c. Δ t  2 =  {(x 2 -x) 2 +(y 2 -y) 2 +(z 2 -z) 2 } + c. Δ t  3 =  {(x 3 -x) 2 +(y 3 -y) 2 +(z 3 -z) 2 } + c. Δ t  4 =  {(x 4 -x) 2 +(y 4 -y) 2 +(z 4 -z) 2 } + c. Δ t Principle of GPS Positioning (X,Y,Z)

Control segment Ground-based monitoring and upload stations Control orbit and timing information

USER It includes all GPS users. User can receive the GPS signals through antenna connected to the receiver and can determine its position on the surface of the earth

User segment GPS Receivers; Compatible software for Planning, Downloading and Processing of GPS receiver data;

GPS Receivers (contd.) Navigation capable of about 12 meter accuracy light-weight, cheap! navigation applications

GPS data processing software Real time Post-processing

GPS SIGNAL CARRIER, f(t) CODE, C(t) NAVIGATIONAL DATA, D(t)

CARRIERS L1 (154 f or 1575.42 MHz) L2 (120 f or 1227.60 MHz)

GPS Coordinate system World Geodetic System, 1984 (WGS84)

GPS receivers Positioning Techniques Absolute Relative Real Time Post-processing

LIMITATIONS Ionospheric delay correction is not possible to compute Weak signal – not available under canopy or under shed Susceptible to interference

GPS is getting popular as a means for collection of data

GPS DATA Reliable Accurate Real-time

GPS Can be used in any conceivable situation Under the sky Where the exact position of any object or phenomena involved .

GPS

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GPS