POWER POINT PRESENTATION ON THEORY OF DGPS i.e. DIFFERENTIAL GLOBAL POSITIONING SYSTEM

POWER POINT PRESENTATION ON THEORY OF DGPS i.e. DIFFERENTIAL GLOBAL POSITIONING SYSTEM

1. Welcome to the World of GNSS Products !!!! PUSHPINDER SHARMA NS TECHNOLOGY AND CONSULTANT New Delhi, India 9717490601

2. LAND SURVEYING Land Surveying is the art of determining the relative positions and distinctive features of part on the surface of earth by means of measurements either linear or angular or both.

3. DGPS vs Total station Total station DGPS Accuracy mm level mm level Accuracy degrade (due to instrument shift) accuracy degrade too much (too many times TS shifts) no accuracy degrade (very few instrument shift) Work range Less than 3 km 5-30 km Work time Day time only 24 hrs a day People strength At least 2 persons 1 person only Time taken on 1 point At least 2 min to store one point (short distance) Less than 1 second to store one point Hydrographic survey Very difficult Very easy

4. GPS vs DGPS Global Positioning System (GPS ) provides the position of an object on the earth. It uses timely signals generated by satellites revolving around the earth . Only one unit which act as receiver i.e., Stand-alone GPS receiver is required, with accuracy of 15-20 m. Differential Global Positioning System (DGPS) is an improvement to GPS. DGPS technology can achieve accuracy in mm. It reduces or eliminates the signal degradation, resulting in improving the accuracy. DGPS relies on two receivers Rover and reference receiver (Base). Rover is the user, and reference receiver is also known as the stationary receiver. www.themegallery.com

5. A stationary receiver is fixed, and its position is known to the system. The satellite information is continuously beamed towards the rover and the base station tower. Base station tower uses its known position to calculate the accurate timing. The stationary receiver sends the information to the rover receiver to rectify the measurements with the help of stationary receiver’s relative position . www.themegallery.com

6. What attracts us to D GPS The relatively high positioning accuracies, from tens of meters down to the millimeter level. The signals are available to users anywhere on the globe: in the air, on the ground, or at sea. Its is a positioning system with no user charges, that simply requires the use of relatively low cost hardware. It is an all-weather system, available 24 hours a day. The position information is in three dimensions, that is, vertical as well as horizontal information is provided.

7. Principle of DGPS All DGPS positions are based on measuring the distance from satellite to DGPS receiver on earth The DGPS receiver determines distance to satellites, when it receives signals from satellites. The position of satellites are monitored and controlled in each nano seconds by the control station, hence the position of satellites in each nano seconds are well defined Hence the only unknown is the position of DGPS receiver on earth.

8. Principle of DGPS To define a position on space we require three parameters, the X, Y, and the Z coordinates. When the the receiver gets signals form three satellites it determines the ranges to respective satellites. The three ranges are the X,Y, & Z coordinates. The receiver gets its position by the method of resection (establishing an unknown point from three known points) By measuring 3 ranges the DGPS receiver will give a 2D positional value ie the latitude and Longitude. But when the DGPS receiver ranges 4 th satellite the receiver will compute positional value in 3D ie Latitude, Longitude and Altitude from a datum by giving the time offset corrections

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10. Different methods used in DGPS Surveying Real Time Kinematic Survey (RTK ) – required dual frequency receivers, with a radio link between base station & rover Static Survey – used for control and geodetic survey ( 20 minutes – 2 hours observation)

11. Finding a position in the past For many centuries Celestial bodies like Sun, Moon and Stars were being observed to define a position on Earth Using Astronomical Theodolite or Navigational sextant observing celestial bodies like Sun ,the Moon & stars ,one can fix a positional value on the surface of earth

12. Advantages of DGPS Surveying Inter-visibility between points is not required Can be used at any time of day or night and in any weather Produces results with very high geodetic accuracy More work can be accomplished in less time and with less man power Limited calculation and tabulation works Large area can be surveyed in short time

13. The First Satellite Positioning System In the 1960’s the US Navy’s NAVigation Satellite System (NAVSAT) also known as TRANSIT was developed to provide more accurate position for ships and submarines. TRANSIT was the first operational satellite positioning system. Six satellites gave worldwide coverage. Accuracy within 200 meters, system operated until 1996

14. Principle of Getting Position Positions are determined by intersecting distances between the GPS satellites and the receiver. Traditionally, the technique is called Trilateration or Resection

15. Early GPS receivers MANPACK GPS Receiver One of the first portable GPS units available to soldiers in the field was the PSN-8 "Manpack" receiver. About 1,400 were manufactured between 1988 and 1993. It weighed more than 25kilo grams and took nearly 20 to 30 minutes for a position fix.

16. Basic Civil Positioning: Before May 2000 C/A Code on L1, Selective availability On GPS IIA, IIR satellites, accuracy 100m 100 m GPS I, GPS II A, &GPS II R

17. Basic Civil Positioning: By 2009 C/A Code on L1, GPS IIR(M) Modified satellites First Launch on 2003, fully operational capacity by 2009 New Civil Code will be added to L2 Accuracy 3-5 meters with code only 3-5 m GPS II R(M)

18. Basic Civil Positioning: By 2014 C/A Code on L1, Civil code on L2, New Code on L5 GPS IIF Satellites, F- for follow on, First launch on 2005, and fully operation in 2014 1-3 m Better resistance to interference GPS II F

19. Basic Civil Positioning: 2018 ? GPS III The next generation GPS satellite GPS-III is in its design phase, First launches expected in 2009 with fully operational capability in 2018. Accuracy may be 0.1m

20. Methods used for GPS Positioning 1. Absolute Positioning This involves the use of single receiver at one station location to collect satellite data to determine the position Not accurate for surveying, accuracy being 25 meters (C/A Code only), 3m(C/A code with L1 carrier) Widely sued for Military and navigational purposes 2. Differential Positioning Requires at least two receivers set up at two stations (one is at a known position called Base station and the other a rover) to collect satellite data simultaneously in order to eliminate the errors. Can provide the accuracies required for surveying and scientific applications

21. Real-time DGPS Real-time DGPS involves two receivers: one placed over a known station, and the known coordinates were fed manually into the receiver . The base station calculate its positional value and calculates the offsets to be given to the satellite ranges to get the actual value. These Offsets(Corrections) were transmitted through a radio modem fitted with the Base station The Rover receiver roving around the field calculates its positional value and receives the corrections from the base receiver. When the rover receiver applies these corrections to the computed value it gets the actual positional value The accepted format for the communication between the Base station and Rovers in DGPS system is RTCM-104 format(Radio Technical Commission for Maritime Services, study committee SC-104)

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23. Post-Processed DGPS In Post Processed DGPS technique there are no radio links between the Base and rover receivers The base receiver as well as the Rover receivers records all the satellite signal data while observation While back in office using a post processing software, taking time as constant, all errors were eliminated and the real coordinates are evaluated. In this method, no radio link between the base and reference receiver is required. Hence this method is widely used for surveying.

24. Observation Station on the RCC Bridge [on Ganga Canal at Roorkee]. Cable stayed bridge on Ganga canal at Roorkee MEASUREMENT OF DEFLECTION OF BRIDGE USING GPS

25. Surveying using DGPS Surveying that previously required hours or even days using conventional methods can be done in minutes with DGPS . DGPS receivers can display time accurate to within 150 billionths of a second

26. DGPS in Civil Engineering In Land Surveying In Hydrographic Surveying In Geo-technical Engg . In Mapping In Traffic Engineering In Transport Planning In Fleet Management In Structural Analysis (Dynamic Analysis) In Geo-technical Engg . In Mapping In GIS applications In Geodetic Studies In Crustal Deformation Studies In Irrigation In Land Management In Disaster management In Railways In Civil Aviation

27. Scientific application of DGPS Scientists use DGPS for a wide range of applications. Scientific analysis that formerly had to be conducted in a laboratory can now be done quicker and easier in the field. In this photograph, a scientist is using DGPS to perform a topographic survey of a volcano in South America .