Course Notes: Overview of GPS


Global Positioning System (GPS) - a radio navigation facility

Satellite Signals

Observables

  1. Pseudorange - distance from the satellite to the receiver plus small corrective terms for clock errors, the ionosphere, the troposphere, and multipath.
  2.  

    Given the geometric positions of the satellites (satellite ephemeris), four pseudoranges are sufficient to compute the position of the receiver and its clock error.

    Pseudoranges are a measure of the travel times of the codes (C/A, P or Y).

  3. Carrier phase - the difference between the received phase and the phase of the receiver oscillator at the epoch of measurement.

 

Classical Navigation

Surveying and Geodesy

Capabilities

Example

Elements of Satellite Surveying

  1. Geocentric Coordinate Systems

    Space-Fixed: motion of earth's rotation axis in space on the basis of a rigid earth model being driven by gravitational pull of sun and moon.

    It is now necessary to model the earth as an elastic shell with liquid core.

    The current set of nutations (mathematical expressions describing the position of the earth's rotation axis in space as a function of time) is the "1980 IAU Theory of Nutation". This theory includes all externally forced motions of the earth's axis.

    Earth-fixed: division of earth's lithosphere (solid outer 100 km) into 20 nearly rigid plates that seem to move independently complicates definition of earth-fixed reference system.

  1. Precision and Nutation

Precision refers to long period motions of the earth's axis of rotation in space.

 

Celestial Coordinate System:

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Sphere of Directions