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Glossary
62 GSR2700 IS Operations Manual
Coarse/Acquisition (C/A) Code— The Coarse/Acquisition (or
Clear/Acquisition) code modulated onto the GPS L1 signal.
D
DOP— See Dilution of Precision (DOP) .
DGPS— See Differential GPS (DGPS) .
Datum— A model of the Earth used for geodetic calculations.
Differential GPS (DGPS)— A technique to improve GPS accuracy. It
primarily uses pseudorange errors at a known location to improve
the measurements made by other GPS receivers within the same
general geographic area.
Dilution of Precision (DOP)— The geometry of the visible satellites
is an important factor in achieving high quality results. The geometry
changes with time due to the relative motion of the satellites. An
accuracy measure for the geometry is the DOP factor.
E
Elevation mask angle— An adjustable feature in GPS receivers that
specifies a satellite must be at least a specified number of degrees
above the horizon before the receiver uses the signals from that
satellite. Satellites at low elevation angles (five degrees or less) have
lower signal strengths and are prone to loss of lock and multipath.
Ellipsoid— A smooth mathematical surface that represents the
Earth’s shape and very closely approximates the geoid. It is used as a
reference surface for geodetic surveys.
Ellipsoidal height— The height above a defined ellipsoid,
approximating the surface of the Earth.
Ephemeris— A set of satellite orbit parameters used by a GPS
receiver to calculate precise GPS satellite positions and velocities. The
ephemeris is used in the determination of the position solution and is
updated periodically. Available as “broadcast ephemeris” or as post-
processed “precise ephemeris”.