CE 316 Geomatics - Chapter 9

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CE 316 Geomatics - Chapter 9
2012-04-09 17:22:11
Geomatics Satellite Positioning

Geomatics - Satellite Positioning
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  1. Define Ambiguity
    The unknown inter number of cycls of the reconstructed carrier phase between the satellites and the sensor at the beginning of the observation
  2. Anti-Spoofing (A.S.)
    When P-codes becomes encrypted and no longer availabe to the civil users
  3. Baseline
    Consists of a pair of stations for which simultaneous GPS data has been collected
  4. C/A Code
    The coarse/acquisition GPS code- a pseudo random (PRN) code transmitted at 1.023 MHz that repeats every milli-second. Each satellite has its own C/A code so that it can be uniquely identified and recieved seperately from other satellites transmitting on the same frequency
  5. Ephemeris
    A list of positions or locations of a celestial object as a function of time
  6. Epoch
    A particular fixed instant of time used as a reference point on a time scale
  7. Alerts
    Indicates the positions of the satellites in view to an observer on the earths surface at a designated time and location
  8. Cut-off angle
    The minimum elevation angle used by the sensor to track GPS satellites
  9. Geomagnetic Activity
    Occurs when solar flares cause irregular ionization of the ionosphere which in turn causes irregular refraction delays of a radiowave passing through the non-homogeneous medium
  10. GDOP
    Geometric dilution of precision
  11. GPS Window
    Th period during the 24-hour day when there are a sufficient number of satellites in view to meet the positioning requirement
  12. Mission
    The manner in which the GPS will be used in the field
  13. Multipath
    Refers to a reflected signal that combines with the true signal resulting in a weaker position
  14. PDOP-Position of Dilution of Precsion
    A numerical indicator of the geometric strength of the satellite constellation in relation to positioning at a certain location
  15. Point Positioning
    The indpendent reduction of observations made by a particular recieer using the pseudorange with information broadcast from satellites
  16. Post Processing
    Computer processing of data ater the observation session
  17. Project
    Description of a survey job. There is no limit to the number of stations
  18. P-Code
    Precise GPS code - usually encrypted and reserved for military applications
  19. What frequency does the P-code run at and what is its repeating interval?
    P-Code is a 10.23 MHz PRN code that repeats every week
  20. PRN (Pseudorandom Noise) Number
    A number assigned by the GPS system designers to a given set of pseudorandom codes. Typically a satellite will keep its PRN indefinitely. Used as a way of labeling satellites.
  21. Pseudorange Measurements
    Measurements made using one of the pseudorange codes on the GPS signal. They provide an unambiguous measure of the range to the satellite including the effects of the satellite and user clock biases.
  22. Selective Availability (S.A.)
    Used to describe the situation when the operators of the GPS system degrade the broadcast GPS message by dithering the clock or orbital information.
  23. UTC Time
    Coordinated Universal Time is a high precision atomic clock standard, with unifirn and "leap" seconds. It is aligned with GMT
  24. Three major componets of the GPS system are:
    • The satellite system
    • The control segment
    • The user
  25. The GPS reciever can compute the transmit time by knowing the _____ time a message was recieved.
    The GPS reciever can compute the transmit time by knowing the exact time a message was recieved.
  26. A GPS is message is assumed to travel at what speed?
    The speed of light
  27. Based on the GPS system for USA, answer the following questions:
    A) What is the minimum number or Satellites?
    B) What is distance from the satellites to Earth?
    • A) 24
    • B) 20200 km
  28. Based on the GPS system for USA how many orbital planes are there, how many satellites follow each plane and at what degree are the satellites inclined with respect to the equator?
    6 orbital planes with 4 satellites each @ 55 degrees inclincation to the equator
  29. What is the expected life of a satellite?
    7.5 years
  30. How many satellites are currently in orbit and healthy?
  31. How many microwave signals are typically emitted from a GPS satellite? What are the names?
    Two microwave signals, L1 and L2
  32. What are the five primary signals from which observations are and used by surveyors and engineers?
    • L1
    • L2
    • L1 C/A
    • L1 P
    • L2 P
  33. Precise Position Systems (PPS) use the ______ signal to measure the ______ delay.
    Precise Position Systems (PPS) use the L2 signal to measure the ionosphere delay.
  34. Which code is unique to each satellite?
    PRN Code
  35. Which code is the basis for civilian GPS?
    C/A Code
  36. Ground stations around the world are used to...
    • Monitor the health of satellites
    • Upload orbital paratmeters to the satellite
  37. Master control stations for the USA GPS are located where?
    • Schriever Air Force Base, Colorado Springs
    • Sunnyvale, California