Geoscience Reference
In-Depth Information
9
Integration of the Global
Positioning System (GPS)
into Agricultural Geophysics
Dorota A. Grejner-Brzezinska
ContentS
9.1 Introduction ......................................................................................................................... 166
9.2 How GPS Works ................................................................................................................. 166
9.3 The Main Components of GPS ........................................................................................... 167
9.4 GPS Signal Characteristics ................................................................................................. 168
9.5 The Primary Error Sources................................................................................................. 170
9.5.1 Atmospheric and Environmental Effects................................................................. 170
9.5.1.1 Ionosphere and Troposphere Delays .......................................................... 170
9.5.1.2 Relativistic Propagation Error .................................................................... 172
9.5.1.3 Multipath .................................................................................................... 172
9.5.2 Satellite and Receiver Clock Errors......................................................................... 172
9.5.3 Orbital Errors........................................................................................................... 172
9.5.4 Receiver Noise, Interchannel Bias, and Other Instrumental Biases ........................ 173
9.5.5 Antenna Phase Center Location .............................................................................. 174
9.5.6 Reference Station Error............................................................................................ 174
9.5.7 Number of Visible Satellites and Their Geometry .................................................. 174
9.5.8 Interference and Jamming (Intentional Interference) .............................................. 175
9.5.9 Intentional Degradation of the Satellite Signal........................................................ 175
9.6 Mathematical Models of Pseudorange and Carrier Phase Observables ............................. 176
9.7 Positioning with GPS .......................................................................................................... 179
9.7.1 Point versus Relative Positioning............................................................................. 180
9.7.1.1 Point (Absolute) Positioning ....................................................................... 180
9.7.1.2 Relative Positioning.................................................................................... 180
9.7.2 DGPS Services: An Overview ................................................................................. 182
9.7.2.1 DGPS Services: Examples ......................................................................... 183
9.7.2.2 DGPS Message Format .............................................................................. 184
9.7.3 Network-Based Real-Time Kinematic GPS (RTK GPS) ......................................... 187
9.7.4 Precise Point Positioning ......................................................................................... 189
9.8 Real Time versus Postprocessing........................................................................................ 190
9.9 How Accurate is GPS? ........................................................................................................ 191
9.10 GPS Instrumentation........................................................................................................... 192
9.11 GPS Modernization and Other Satellite Systems ............................................................... 194
9.12 GPS Mapping Project and Connection to Agricultural Geophysics................................... 194
Acknowledgments.......................................................................................................................... 196
References ...................................................................................................................................... 196
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