Surveying

1. Surveying www.powerpointpresentationon.blogspot.com

2. What is Surveying Surveying has traditionally been defined as the science, art, and technology of determining the relative positions of points above, on , or beneath the earth’s surface, or of establishing such points. Surveying can be regarded as that discipline which encompasses all methods for measuring and collecting information about the physical earth and our environment, processing that information , and disseminating a variety of resulting products to a wide range of clients. Surveying processional activities involve on, above, or below the surface of the land or the sea, and may be carried out in association with other professionals.

3. History of Surveying • 1.Germination About 1400 B.C. • 2.The Earth’s Size and Shape 200 B.C. • 3.Development of Science of Geometry 120 B.C. • 4.Roman Engineer and Surveyor The first century 5.New technologies 18th and 19th century

4. Importance of Surveying • Map the earth above and below sea level • Prepare navigational charts • Establish property boundaries • Develop data banks of land-use and • natural resource information • Determine facts on the size, shape, gravity, • and magnetic fields • Prepare charts of our moon and planets

5. Classification of Surveying Plane Surveys • Plane Survey instruments are very simple, • Consisting of a plane table, • A small drawing table mounted on a tripod • A table can be leveled and rotated. • This provided a base for the alidade, the telescopic surveying device from which observations were made.

6. Plane Surveys • The rotation of the alidade was analogous to the rotation of a compass, • it provides a horizontal angle, • i.e. a compass direction. • The locations of lines and points are plotted directly on the drawing paper. • Setting up the table must be leveled • it is oriented correctly with a reference meridian (e.g. north line). • The table is moved and re-oriented at each station along the survey route.

7. Geodetic Surveys • Covers distances large enough that • curvature of Earth is significant • Establishes network of precisely located controlpoints

8. National Geodetic Survey • Functions: • Defines & manages the National Spatial Reference System • Sets standards for geodetic surveys • Maintains a database of U.S. geodetic markers

9. Uses for plane surveys • Land survey • Engineering or construction surveys • Field mapping

10. Specialized Types of Surveys • Control surveys • Topographic surveys • Land, boundary, and cadastral surveys • Hydrographics surveys • Route surveys • As-built surveys • Mine surveys • Solar surveys • Optical tooling • Ground, aerial, and satellite surveys

11. New Technologies for Surveying and Mapping • Electronic Total Station Instruments • Global Positioning System (GPS) • Digital Photogrammetric Systems • Land and Geographic Information system • (LIS/GIS)

12. Federal Surveying and Mapping Agencies • NGS – National Geodetic Survey • USGS – United States Geological Survey • BLM – Bureau of Land Management • U.S. Army Corps of Engineers • Forest Service • National Park Service • International Boundary Commission, • Bureau of Reclamation • Tennessee Valley Authority • Mississippi River Commission • U.S. Lake Survey • Department of Transportation

13. Professional Surveying Organizations • ACSM (American Congress on Surveying and Mapping) • ASPRS (American Society of Photogrametry and R S) • Geomatics Division of the ASCE (American Society of Civil Engineers) • Urban and Regional Information Systems Association (URISA) • CIG (Canadian Institute of Geomatics) • FIG (Federation Internationale des Geometres)

14. Theodolites Theodolites are used to measure horizontal angles like the plane table, also calculate vertical angles, from which elevations could be derived. Theodolites are much lighter and did not require the construction of the hardcopy map in the field. While the purpose of transits and theodolites are similar, as a general rule a theodolite is more accurate than a transit.

15. What is Total Station A Total Station integrates the functions of a theodolite for measuring angles, an Electronic Distance Meter for measuring distances, digital data and information recording.

16. Functions of Total Station • Measure angle and distance accurately and quickly • Make computation with angle and distance • Display the results in real time • Widely be used for topographic, hydrographic, cadastral, and construction surveying

17. Characteristics of Total Station Instruments • 1. Three basic components • Electronic distance measuring • Electronic angle measuring • Microprocessor

18. Characteristics of Total Station Instruments 2. Functions • Horizontal angle, Vertical angles, Slope distance • Horizontal distance, vertical distance, elevation, coordinates of point • Display the results on a LCD

19. Functions Performed by TSI • Human-Computer Interactive Design • Assisting an operator to operate the instrument • Prompting by display on LCD • Micro-Processor Computation • Averaging of multiple angles and distance measurements • Correcting measured distances • Prism constants • Atmospheric pressure • Temperature

20. Functions Performed by TSI • 3. Making curvature and refraction correction to elevation determined by trigonometric leveling • 4. Reducing slope distances to their horizontal and vertical components • 5. Calculating point elevations (input instrument height) • 6. Computing coordinates of surveyed points from horizontal angle and horizontal distance components

21. Parts of A TSI • Telescopes: • Angle measurement system • Vertical circle • Rotation of the telescope • Tri-branch • Bases of total stations • Optical plummet • Tripods • Microprocessor • Keyboard and display • Communication port

22. Sources of Error In Total Station Work • Instrumental Errors • Personal Errors • Natural Errors

23. Instrument Errors Instrumental errors are caused by imperfections in the design, construction, and adjustment of instruments and other equipment 1. Instrument axes are not perfectly parallel or 2. Imperfect linear or angular scales. perpendicular to each other. 3. Misalignment of various part of the instrument. 4. Optical distortions causing “what you see is not exactly what you are supposed to see”.

24. Instrumental errors are eliminated by • Using proper procedures, such as observing angles in direct and reverse modes • Balancing foresights and back sights and repeating measurements • Periodically checked, tested and adjusted (or calibration) 

25. Human Errors • Human errors are caused by the physical limitations of the human senses of sight andtouch, e.g. error in the measured value of a horizontal angle, caused by the inability to hold a range pole perfectly in the direction of the plumb line. • Error can be minimized by • Common sense • Self-calibration (estimating personal errors by • experiments and experience) • Attention to proper procedures

26. Natural Errors Natural errors result from natural physical conditions such as atmospheric pressure, temperature, humidity, gravity, wind, and atmospheric refraction Natural errors are mostly systematic and should be corrected or modeled in the adjustment.  Some natural errors such as the effect of curvature and refraction can be eliminated by a procedure.  The leveling procedure to eliminate curvature and refraction corrections is to average foresights and back sights

27. Global Positioning System • GPS Basics • What is GPS • How Does it Work?

28. Global Positioning System • 24 satellites orbiting earth in 12 hours • Constellation provides 5 to 8 visible satellites from any point on the earth • 4 satellites are required to compute the 3 dimensions of position and time stamp • Precision ranges from 10 m to 100 m depending mainly on Selective Availability and Ionospheric effects

29. GPS Global Positioning System (NAVSTAR - DOD) A network of satellites that continuously transmits coded information, which makes it possible to precisely identify locations on earth by measuring distance from the satellites

30. SPACE SEGMENT The first GPS satellite was launched in 1978 constellation of 24 satellites since 1994 each satellite is built to last about 10 years 2,000 pounds, 17 feet across with the solar panels extendedpowered by solar energy continuously broadcast coded radio signal

31. High orbit satellites (about 12,000 miles above earth surface) traveling 7,000 miles per hour allows them to circle earth once every 12 hours Arranged in orbit so as to provide coverage by 4 satellites at once Each satellite transmits low power radio signals on several frequencies (L1, L2 0 Civilian GPS receivers listen on L1 frequency Need to be able to receive the signal so not in buildings, underwater, caves Signal will pass through clouds or glass, but not solid objects (line of sight)

32. L1 contains two pseudo-random signals The Protected (P) code and the Coarse/ Acquisition code (C/A) scrambling of the P code Each satellite transmits a unique code Use these coded signals to calculate travel time from the satellite to the GPS receiver CONTROL SEGMENT Ground based Control Stations track the GPS satellites and provide them with corrected orbital and clock (time) information

33. Unmanned stations receive info and send to master Ground based Control Stations track the GPS satellites and provide them with corrected orbital and clock (time) information Master corrects satellite data and sends uplinks to GPS satellites GPS receiver calculates its position by measuring the distance to satellites (satellite ranging)

34. To calculate our position we need to know satellite location and satellite distance Along with the radio signal, the GPS receiver picks up two kinds of coded information from the satellites Almanac data contains the approximate position of the satellites Stored in the memory of the GPS receiver so it knows where each satellite is suppose to be

35. Ground stations send orbital info to master station Master sends corrected info to satellites Corrected and exact position is ephemeris data From the almanac and ephemeris data GPS receiver knows location of satellites at all times

36. Measuring Distance to Satellite • measures time for signal to travel from satellite to receiver • Speed of light x travel time = distance • Distance measurement to 4 satellites are required to compute a 3- D position (latitude, longitude and altitude)

37. When satellite is generating code so is receiver Measuring Travel Time of Satellite Signals Receiver compares the two codes to determine how much it needs to shift (delay) its code to match the satellite code

38. Uses measurements from 4+ satellites distance = travel time x speed of light

39. Sources of Error 1.Atmospheric Interference signal slows as it passes through atmosphere Picture Use model to correct

40. 2.Multipath Errors Multipath means that the same radio signal is received several times through different paths. For instance, a radio wave could leave a satellite and travel directly to the receiver, but it also bounces off a building and arrives at the receiver at a later time.

41. 3.Clock Limitations The internal satellite and receiver clocks have limited accuracy, and they are not precisely synchronized. Since position computations are highly dependent on accurate timing information, small clock errors can cause significant errors in position computations.

42. 4.Ephemeris Error (Orbital errors) Inaccuracies in reported position of satellite

43. 5.Satellite Configuration The configuration of the satellites in view to a receiver can affect the accuracy of position determination. For instance, if all of the visible satellites happen to be bunched close together, the triangulated position will be less accurate than if those same satellites were evenly distributed around the visible sky.

44. 6. Selected Availability Scrambling of signal by military • HOW ACCURATE is GPS • Depends on some variables • Time spent on measurements • Design of receiver • Relative position of satellites • Use of Differential Techniques

45. High correlation in Time & Space 3 – 4 m (night)20 – 30 m (day) Ionospheric delay High correlation in Time & Space 3 m Tropospheric delay GPS error sources Error source Error range Correlation Impact Ephemeris error 3 m Satellite Clock These errors can be corrected by “Augmentation Systems”

46. Differential GPS Place a GPS receiver (reference or base station) at a known location. This base station receiver will calculate receiver errors by comparing its actual location to the location computed from the signals. This error information is sent to the rover receiver, which uses it to correct the position information it computes from the signals. Accuracies of DGPS systems can range from 15 feet to 3 feet depending on system configuration.

47. Differential GPS in Action 1.Compares field data to data collected at the same time at a nearby base station 2.Error at base station known and subtracted from field data

48. GPS Error Budget Typical Error in Meters (per satellite) Standard GPS Differential GPS Satellite clocks 1.5 0.0 Orbital errors 2.5 0.0 Ionosphere 5.0 0.4 Troposhpere 0.5 0.2 Receiver noise 0.3 0.3 Multipath 0.6 0.6 Selective availability* 30 0.0 Typical Position Accuracy Horizontal 50 1.3 Vertical 78 2.0 3-D 93 2.8 * No longer used

49. Defining a Location Latitude and Longitude units of measurement are Degrees Degree is divided into 60 Minutes Minute is divided into 60 Seconds

50. Latitude 42° 23’ 50.4” N Longitude 71° 7’ 32.8” W To convert coordinates from degrees, minutes, seconds format to decimal format, use this easy formula: degrees + (minutes/60) + (seconds/3600) Latitude 42.39733 N Longitude 71.12578 W