The receivers can be fixed on the Earth, in moving vehicles, aircraft, or in low Earth-orbiting satellites. GPS is used in air, land and sea navigation, mapping, surveying and other applications where precise positioning is necessary. The GPS Interface Control Document is a government document that contains the full technical description of the interface between the satellites and the user. Ionosphere The band of charged particles 80 to 120 miles above the earth's surface, which represents a nonhomogeneous and dispersive medium for radio signals. Ionospheric Delay A wave propagating through the ionosphere experiences delay.
Phase delay depends on electron content and affects carrier signals.
The phase and group delay are of the same magnitude but opposite sign. The change in the propagation speed of a signal as it passes through the ionosphere. Kalman Filter An optimizing mathematical procedure used to recursively estimate dynamically changing parameters, such as position and velocity track in the presence of noise. The group of radio frequencies extending from 390 MHz to 1550 MHz. Multipath Interference caused by reflected GPS signals arriving at the receiver, typically as a result of nearby structures or other reflective surfaces.