GLOBAL POSITIONING SYSTEM

The positioning system used for all the major services offered will be GPS (Global
Positioning System), which is an all weather, radio based, satellite navigation
system that enable users to accurately determine three-dimensional position.
The Global Positioning System’s primary mission is to provide passive global
positioning and navigation for land, air, and sea based strategic and tactical
forces. The GPS receiver measures distances between satellites and itself to
determine the receiver’s position from intersections of the multiple range vectors.
Distances are determined by accurately measuring the time, which a signal pulse
takes to travel from satellite to the receiver.
The GPS receivers use the satellites as reference points for triangulation their
position on earth. The position is calculated from distance measurements to the
satellites that are determined by how long a radio signal takes to reach the
receiver from the satellite. To calculate the receiver’s position on earth, the
satellite distance and the satellite’s position in space are needed. The satellites
transmit signals to the GPS receivers for distance measurements along with the
data messages about their exact orbital location and operational status. The
satellites transmit two “L” band frequencies for the distance measurement
signals called L1 and L2. Minimums of four satellite observations are required to
mathematically solve the four unknown receiver parameters (latitude, longitude,
altitude and time).
At a known geographical benchmark, one GPS receiver is programmed with the
known coordinates and stationed over the geographical benchmark. The
receiver, known as the master or reference unit, remains over the known
benchmark, monitors the movement of the rover (secondary mobile GPS
receiver), and calculates its apparent geographical position. The inherent errors
are determined relative to the master receiver's programmed position and the
necessary corrections or differences are transmitted to the rover.