Navyasree Nuthalapati*
Receivers equipped to measure dual frequency phase signals from satellites of the Global Positioning System have been capable, under special conditions, of determining relative horizontal positions among stations separated by one to few hundred kilometers with precision of one to several millimeters, Global Positioning System originally Navstar GPS is a satellite-based radio navigation system owned by the us government, global navigation satellite systems which provide geo location and time information to a GPS receiver anywhere on the Earth surface where there is an line of sight to four or more GPS satellites Obstacles such as mountains and buildings block relatively weak GPS signals Receivers used to measure under special conditions, for determining relative horizontal positions between the stations divided by few hundred kilometers of several millimeters, Major obstacles making this capability extending it to all parts of the globe, and longer station separations, equipment cost, limitations in the uncertainties in satellite orbits, data analysis GPS satellite constellation propagation delays associated with variable tropospheric, stratosphere, water vapor, and difficulties in resolving carrier phase cycle.
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