1. Surveying Instruments
Mechanical
Tape
Opto-Mechanical
Level
Transit/Theodolite
Electronic
Electronic Distance Measuring
Total Station
GPS: Satellite Assisted Systems
11/24/2018
AHT/EVC

2. Some Oldies
11/24/2018
AHT/EVC

3. Some Oldies
11/24/2018
AHT/EVC

4. Some Oldies
11/24/2018
AHT/EVC

5. Some Oldies
11/24/2018
AHT/EVC

6. Some Oldies
11/24/2018
AHT/EVC

7. Some Oldies
11/24/2018
AHT/EVC

8. Some Oldies
Wireless Communication Technology
11/24/2018
AHT/EVC

9. Electronics Devices Electronic Distance Meter 11/24/2018 AHT/EVC d
Two-way ranging by EDM
one clock used to measure D t
Two way travel time:
t=2d/c.
Distance: d=c
t/2
11/24/2018
AHT/EVC

10. Total Station
11/24/2018
AHT/EVC

11. GPS in Land Surveying

12. 11/24/2018
AHT/EVC

13. What is GPS? A system capable of providing position
information anywhere on earth –
Global Positioning System
Relies on using a constellation of orbiting satellites
(various orbits around the earth)
User receivers acquire signal and determines position
11/24/2018
AHT/EVC

14. GPS Global Positioning System Developed by DOD Cost $10 billion
Triangulation-based technology
GPS was developed by the Department of Defense, specifically the US Air Force and the US Navy at a cost of approximately $10 billion (the motivation was the positioning of nuclear submarines). The basis of the technology is roughly the same as that used by LORAN and SATNAV…that is triangulation!
GPS consists of a constellation of 24 satellites, 21 active and 3 spares. All orbit the earth at 11,000 miles above the earth.
11/24/2018
AHT/EVC

15. Why use it? AAA (who can resist it!) Economical Increased Productivity
All weather operation
Always available (24/7 operation)
Anywhere available
Economical
Increased Productivity
Improved Customer service
Accuracy (3-D data, Velocity and timing)
11/24/2018
AHT/EVC

16. Who Uses it?
Land, sea, and airborne navigation, surveying, geophysical exploration, mapping and geodesy, vehicle location systems, farming, transportation systems
Telecommunication infrastructure applications include network timing and enhanced 911 for cellular users
Global delivery of precise and common time to fixed and mobile users
11/24/2018
AHT/EVC

17. Some Applications
11/24/2018
AHT/EVC

18. Some Applications
11/24/2018
AHT/EVC

19. Some Applications
11/24/2018
AHT/EVC

20. Some Applications
11/24/2018
AHT/EVC

21. Some Applications
11/24/2018
AHT/EVC

22. Some Applications
11/24/2018
AHT/EVC

23. Some Applications Could be used to track mail if properly used!
11/24/2018
AHT/EVC

24. Some Applications
11/24/2018
AHT/EVC

25. Some Applications
11/24/2018
AHT/EVC

26. Some Applications
Mapping
11/24/2018
AHT/EVC

27. The GPS System Components The User Segment The Control Segment The Space Segment
11/24/2018
AHT/EVC

28. The Space Segment
11/24/2018
AHT/EVC

29. The Space Segment Constellation of 24 satellites orbiting the earth
Six orbital planes with four satellite per orbit
Seven satellites are typically visible 10 degrees or more above the horizon
Satellites orbit the earth about every 12 hours
11/24/2018
AHT/EVC

30. Satellite Constellation
11/24/2018
AHT/EVC

31. GPS Satellite
11/24/2018
AHT/EVC

32. Basic Concept
Satellites are reference points to locations on earth (their location are known)
A location of a point on earth is identified by “triangulation”
Signals from three satellites are used
Travel time of each signal is determined
Signals travel at Speed of light
Distance = Travel Time * Speed of Light
11/24/2018
AHT/EVC

33. Triangulation (2-D)
11/24/2018
AHT/EVC

34. Triangulation (3-D) 3 satellites 11/24/2018 AHT/EVC
We can see now that the area intersected by all three spheres is quite small. In actually, with this configuration the surface of the spheres only meet at two points. One will be at the surface of the earth, the other somewhere either in space or within the earth. This second point is a nonsense point, however the computers cannot determine a nonsense point from a truly meaningful point. So, we need 1 more satellite!
With 4 satellites we will find only 1 point of intersection. This is the real point and the nonsense point can be discarded. The fourth satellite also always GPS to estimate elevation…so not only can be obtain an X and Y estimate, but also a Z estimate.
Note: The Z estimate has an error of about 1.5 times the error that of the X,Y estimate.
11/24/2018
AHT/EVC

35. The Triangulation Equation
3 variables
Where, exactly, are the satellites
How long it takes the radio signal to travel that distance
How far is the point from the satellite
We already said that GPS uses triangulation. This ‘equation’ contains 3 variables.
1) How far is the point from the satellite
2) How long does it take for a radio signal to travel from the satellite to the point on the earth.
3) Where, exactly, are the satellites located.
This equation also contains a correction factor because radio waves travel at the speed of light only in a vacuum (space). When they travel through our atmosphere they slow down. So our triangulation equation must account for this.
11/24/2018
AHT/EVC

36. Where are the satellites?
From orbital mechanics, the location of satellites are determined
An almanac of orbital information for all satellites are stored in each satellite
Ground control-stations continuously update location information of each satellite and transmit it to them (i.e. ephemeris)
11/24/2018
AHT/EVC

37. GPS Codes & Carriers
11/24/2018
AHT/EVC

38. Pseudoranging
11/24/2018
AHT/EVC

39. What is the Distance? Range (distance) = Time * Speed of Light
Three satellites will provide
Latitude
Longitude
Height
Fourth satellite is needed to account for clock time difference – solve for time
11/24/2018
AHT/EVC

40. Pseudoranging to four Satellites
11/24/2018
AHT/EVC

41. Accuracy of Pseudoranging
P code – 10 meters
C/A code – 20 to 30 meters
With Selective Availability (SA) – 100 meters
SA was turned off since 2000
Other techniques are needed to improve accuracy:
Carrier Phase measurement (Surveying)
Differential GPS
11/24/2018
AHT/EVC

42. Sources of Error Atmospheric scattering Clock errors Receiver errors
Multi-Path Interference
Ephemeris
GDOP SA
Now we have solved the equation and we have an estimate for the X,Y and Z of our location.
How accurate is this estimate? Can we even guess at the absolute accuracy with the information we have?
Let’s look at the sources of error in GPS locations.
1) Ionospheric scattering: Remember we said that radio waves do not travel at the speed of light in our atmosphere. Well, the ionosphere (a sphere of charged particles) has quite an influence on the radio waves. By itself it accounts for approximately +/- 4 meters of error.
2) Tropospheric scattering: Another portion of the atmosphere also affects accuracy. Not to the extent of the ionosphere but some effect is felt here as well.
3) Errors in the clocks: The atomic clocks on-board the satellites are the best we have but they are still not perfect. This error amounts to approximately +/- 0.7 meters.
4) Receiver errors: The GPS receiver can also effect your accuracy. This is a result of electrical component tolerances and component quality. This error is approximately +/- 1 meter.
5) Multi-Path Interference: This error is analogous to ‘ghosting’ or interference you may have noticed in your television or radio.
6) Ephemeris: errors in the prediction of the satellites location.
7) Geometric Dilution of Precision (GDOP): We will discuss this next. It causes approximately +/- 1-2 meters of error.
8) Selective Availability (SA): We will discuss what this means later as well as how much error can arise from this source.
11/24/2018
AHT/EVC

43. Multi-path Error
11/24/2018
AHT/EVC

44. GDOP (Geometric Dilution of Precision)
11/24/2018
AHT/EVC

45. Differential GPS (DGPS)
Two receivers used simultaneously
One located at a control station (or a monument) where the coordinates are precisely known (base station)
One is located at a survey point where coordinates are desired
Both stations measure distance
Base station calculates error and transmits it to the survey station
11/24/2018
AHT/EVC

46. DGPS
11/24/2018
AHT/EVC

47. Errors Compensated
The adjustments made by DGPS technique represents a net sum of various errors present in the process.
This correction doesn’t address problems with the receiver clocks
This correction may not be sufficient when the receiver and the base station are too far from each other
11/24/2018
AHT/EVC

48. Grouping of Survey Points
11/24/2018
AHT/EVC