Viavi 87339, Руководство по эксплуатации

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Data Message
Also known as the Navigation Message. A 1500 bit message modulated
on the L1 and L2 GPS signal, which contains the satellite's location (or
ephemeris), clock (bias) correction parameters, constellation almanac
information and satellite health.
Differential GPS (DGPS) A technique to improve GPS accuracy that uses pseudo-range errors
measured at a known Base Station location to improve the
measurements made by other GPS receivers within the same general
geographic area. It may be implemented in real-time through the
provision of a communication link between the GPS receivers,
transmitting the correction information in the industry-standard RTCM
format, or various proprietary formats. May be implemented in single
Base Station mode, in the so-called Local Area DGPS (LADGPS), or
using a network of Base Stations, as in the Wide Area DGPS (WADGPS)
implementation.
Dilution of Precision
(DOP)
An indicator of satellite geometry for a unique constellation of satellites
used to determine a position. Positions tagged with a higher DOP value
generally constitute poorer measurement results than those tagged with
lower DOP. There are a variety of DOP indicators, such as GDOP
(Geometric DOP), PDOP (Position DOP), HDOP (Horizontal DOP),
VDOP (Vertical DOP), etc.
Dithering The introduction of digital noise into the system. "Clock dithering" is the
process by which the U.S. Department of Defense (DoD) degrades the
accuracy of the Standard Positioning Service (i.e. absolute positioning
of a C/A-Code capable receiver). "Clock dithering" is the additional
satellite clock "bias" induced by the DoD's "Selective Availability" policy
that cannot be corrected for by the broadcast Navigation Message clock
correction parameters.
Doppler Shift
The apparent change in the frequency of a signal caused by the relative
motion of the transmitter and receiver.
Dual Frequency Refers to the instrumentation that can make measurements on both
L-Band frequencies, or to the measurements themselves (e.g., L1 and
L2 pseudo-range or carrier phase measurements). Dual-frequency
measurements are useful for high precision (pseudo-range-based)
navigation because the Ionospheric Delay bias can be determined, and
the data corrected for it. In the case of Double-Differenced carrier
phase, dual-frequency observations can account for the residual
ionospheric bias (for case of long baselines), or aid Ambiguity
Resolution for "rapid static" or "kinematic" baseline determination. All
"top-of-the-line" GPS receivers are of the dual-frequency variety, and
are comparatively expensive because of the special signal processing
techniques that must be implemented to make measurements on the L2
carrier under the policy of Anti-Spoofing.
Enhanced Keplerian
Elements (ephemeris)
Those elements which describe the position of a satellite in a different
orbit and which comprise the standard Keplerian elements (q.v) and
harmonic correction terms for the argument of latitude, orbit radius and
inclination angle.
Ephemeris (plural:
Ephemerides)
The file of values from which a satellite's position and velocity (the
so-called "satellite state vector") at any instant in time can be obtained.
The "Broadcast Ephemeris (or Ephemerides)" for a satellite are the
predictions of the current satellite position and velocity determined by
the Master Control Station, uploaded by the Control Segment to the GPS
satellites, and transmitted to the user receiver in the Data Message.
"Precise Ephemeris (or Ephemerides)" are post-processed values
derived by, for example, the International GPS Service (IGS), and
available to users post-mission via the Internet.
Fix
A single position with latitude, longitude (or grid position), altitude (or
height), time, and date.
Geometric Dilution of
Precision (GDOP)
An indicator of the geometrical strength of a GPS constellation used for
a position/time solution.
Term Description