This lesson provides a technical introduction to Global Navigation Satellite Systems (GNSS), covering theory, procedures, and accuracy issues. Aimed at professionals in a “geospatial science” field, including engineers, surveyors, meteorologists, geographers and GIS professionals, it will also be useful for emergency managers, and technically-inclined members of the general public with appropriate math and/or science background. For those who may currently see GPS/GNSS as a “black box”, this 1.5 hour lesson provides an understanding of the underlying principles and concepts to support correctly interpreting GPS results and obtaining accurate measurements under various circumstances.
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Overall: Explain professional tools and methods, as well as underlying concepts of global navigation satellite systems (GNSS) and how they are used to achieve accurate and precise horizontal and vertical positioning results.
Unit 1
- Identify the key components of a GNSS system and the function of each.
- Explain the principles of trilateration as used in GNSS-enabled positioning.
Unit 2
- Explain how the receiver determines the identity and location of each satellite using the navigation message and signal-matching.
- Explain the process for estimating pseudorange using PRN code synchronization.
- Describe how estimated position is calculated using pseudoranges.
Unit 3
- Describe how wavelengths are used for precise distance measurement.
- Describe the use of phase measurement and counting cycles to obtain precise distance measurement to the satellite.
- Explain how post-processing services such as NOAA’s OPUS are used to increase accuracy and reduce positioning error.
Unit 4
- Describe different potential error sources in GNSS operation and how they are mitigated:
- GPS satellite and receiver clock errors
- Ionospheric delay
- Satellite orbital errors
- Tropospheric error
- Multipath errors
- Explain how increased observation time increases the accuracy of GNSS-derived position.
- Explain how the mathematical process of of double differencing is used to increase accuracy and reduce errors.
- Explain the role of continuous GNSS active-relative positioning systems such as NOAA’s CORS.
Unit 5
- Describe a reference frame (or datum) and how it is used in GNSS.
- Describe the process of converting between Cartesian coordinates (X,Y,Z) and positions (latitude, longitude, ellipsoid height).
- Explain why, for most applications, heights should be converted from an ellipsoidal to an orthometric reference frame.
national geodetic survey, geodesy, NGS, GPS, GNSS, GLONASS, trilateration, navigation message, signal-matching, pseudorange, PRN code, satellite clock bias, receiver clock bias, satellite clock bias, wavelength, phase measurement, integer count, integer ambiguity, integer ambiguity resolution, OPUS, positioning error, L1/L2, Ionospheric delay, satellite orbital errors, tropospheric error, multipath errors, double differencing, CORS, continuously operating reference stations, reference frame, datum, Cartesian coordinates, vertical datum, ellipsoidal heights, ellipsoid, ellipsoid height, geoid, orthometric, orthometric height, orthometric reference frame, elevation measurement, reference surface, NAVD88, NAVD 88, official U.S. datums, U.S. Global Positioning System, Global Navigation Satellite Systems, World Geodetic System 1984, WGS 84, WGS84
