GPS stands for Global Positioning System, and it is a space based geodetic tool used to measure precisely a position at any point on the earth with respect to a geodetic datum. Fundamentally GPS measure the distance called the range between a receiver on the ground and a few simultaneously observed satellites. The initially measured ranges are called the pseudo ranges and later subject it to post processing and converted it into ground antenna position information.
The backbone of Global Positioning System is the space segment which consists of a set of 24 global positioning satellites revolving around the earth in 12 Hr period in near circular orbits at an altitude of roughly 20,000 km in six orbital planes at an angle of 55 degrees. Besides the space segment there are control and user segments. The control segment basically estimates the satellite ephemeredes, the clock behavior and also monitors the general health of the satellites, while the user segment is equipped with an antenna and a receiver. The transmitted signals from the satellite in the L band frequencies were received by the user antenna placed over a point on the ground and transfer the signal information to the receiver and stored in its memory. Later the stored signal information such as the signal travel time from the satellite to the ground receiver, the satellite code, polarization, clock information etc., are retrieved and decoded by subjecting the raw data into various levels of processing according to the user requirements. The whole GPS system is owned by the U. S Department of Defense.
Applications
Due to high accuracy, economy of operation and its versatility, the applications of GPS in earth sciences are enormous. A few of them are listed below:-
Determination of precise geoid using GPS data
Earth motion and polar motion studies
Surface deformation studies, especially in tectonically active area.
Estimating gravity anomalies
Earthquake monitoring through crustal deformation studies of the order of a few cm/year
Establishing highly accurate vertical benchmark points.
To study the atmospheric precipitable water vapour
Ionospheric tomography
Material needed :
A dedicated computational lab equipped with UNIX high end machines.
A good and fast internet connection.
An antenna and receiver testing room with sufficient storage space of its accessories.