ashtech DG14, Reference Manual

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352 DG14 and DG16 Board & Sensor Reference Manual
Tropospheric correction.
The correction applied to the
measurement to account for
tropospheric delay. This value is
obtained from the modified Hopfield
model.
True anomaly
The angular distance, measured in the
orbital plane from the earth's center
(occupied focus) from the perigee to
the current location of the satellite
(orbital body).
Universal Time Coordinated (UTC)
Time as maintained by the U.S. Naval
Observatory. Because of variations in
the Earth's rotation, UTC is sometimes
adjusted by an integer second. The
accumulation of these adjustments
compared to GPS time, which runs
continuously, has resulted in an 11
second offset between GPS time and
UTC at the start of 1996. After
accounting for leap seconds and using
adjustments contained in the
navigation message, GPS time can be
related to UTC within 20 nanoseconds
or better.
User Range Accuracy (URA)
The contribution to the range-
measurement error from an individual
error source (apparent clock and
ephemeris prediction accuracies),
converted into range units, assuming
that the error source is uncorrelated
with all other error sources. Values
less than 10 are preferred.
UT
Universal Time
UTM
Universal Transverse Mercator Map
Projection. A special case of the
Transverse Mercator projection.
Abbreviated as the UTM Grid, it consists
of 60 north-south zones, each 6 degrees
wide in longitude.
VDC
Volts Direct Current
VDOP
Vertical Dilution of Precision. See
Dilution of Precision and Position
Dilution of Precision.
WGS
World Geodetic System
World Geodetic System 1984 (WGS-84)
A set of U.S. Defense Mapping Agency
parameters for determining global
geometric and physical geodetic
relationships. Parameters include a
geocentric reference ellipsoid; a
coordinate system; and a gravity field
model. GPS satellite orbital information
in the navigation message is referenced
to WGS-84.
World Geodetic System (WGS-72)
The mathematical reference ellipsoid
previously used by GPS, having a
semimajor axis of 6378.135 km and a
flattening of 1/298.26.