## Wednesday, October 7, 2009

### PowerPoint Presentation On GPS

PPT On GPS

GPS Presentation Transcript:
1. Introduction
GPS is the Global positioning system is to determine your position on earth :east- west north-south and vertical(longitude,latitude and altitude). GPS is provided on mid 1990. Today many different standard was used which are WAAS LAAS DGPS NDGPS. DGPS is used to correct bias errors at one location with major bias error at one position. Local area augmentation system focus its service on the airport area. It work using very high frequency radio data link.

2. Basics of GPS
In order to understand how the GPS system works we use for this high school physics. If we send out a pulse of sound or radio waves then we can determine resistance of object by dividing the time it took for reply by the speed of sound. Distance = speed * time Time = Distance/ Speed GPS works on much the same principle. GPS satellite only transmit timing data pulse, GPS receive units, only receive.

3. Shouting From the Stars
The GPS works on this principle, although it uses much more precise clocks and the speed of light. If each GPS unit had to have an atomic clock, it would be expansive. With three satellites we can solve three of these four variables. X, Y = Horizontal Position Z = Altitude T = Time With only three satellites and an imprecise clock, we have to assume altitude to be a known constant. Eg: Sea level. Since we can only solve for three variables using three satellites X , Y and Time. But if we have four visible satellites we can solve for all four variables X, Y, Z and T.

4. Contd-
GPS signals work in microwaves bands. They can pass through glass, but are absorbed by water molecules and reflect off concrete, steel and rock. This means that GPS unit have trouble operating in rain forest, urban jungle, deep canyons, inside automobiles and roads and in heavy snowfalls-among other things. These environmental obstacles degrade positional accuracy or make it impossible to get a fix on your location.

5. GPS ELEMENTS
GPS elements consist of three basic parts: Space segment User segment Control segment

6. Space segment
Space segment of the system consist of the GPS satellites. These space vehicles (vs.) send radio signal from space. The nominal GPS operation constellation consist of 24 satellites that orbit the Earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to repeat older satellites. The satellites orbit repeats all most the same ground track once each day the orbit altitude is such that satellite repeat the same track. There are six orbital plane equally spaced (60 degree apart) and inclined at about 55 degree with respect to the equatorial plane

7. User segment
User segment consist of receivers, which you can hold in your hand or mount in your path. The GPS receiver converts SV signals into position, velocity and time. Four satellites are required to compute the 4 dimensions: X, Y, Z and Time. GPS receivers are used for navigation, position, time and other research.

8. Control segment
Control segment consist of a system of tracking stations located around the world. These stations measure signals from the sves which are incorporated into orbital model for each satellites. The models compute precise orbital data and sv clock correction for each satellites. The master clock station uploads ephemeris and clock data to sves. The master control facility determines the orbit and clock parameters using measurements from five monitor stations distributed around the world.

9. GPS Error sources
There are various types of error in GPS . These are: Satellite clock Receiver clock Satellite orbit error Atmospheric error: Ionosphere and troposphere Multi-path errors These errors in the satellites produce error in distance measurements Satellite clock error