A-8
GG Surveyor GPS+GLONASS Reference Manual
Navigation Modes (Availability & Accuracy)
The GG Surveyor has 12 parallel channels for tracking GPS satellites, and 12 parallel
channels for tracking GLONASS satellites. With this capability, the GG Surveyor
always uses the best available constellation to provide the most accurate position. The
greatest accuracy is obtained when differential corrections are available for both GPS
and GLONASS satellites. The GG Surveyor can be used as a reference station to
generate RTCM corrections for GPS and GLONASS, and a GG Surveyor can use
RTCM corrections for both systems. If differential corrections are available for only
one satellite system (either GPS or GLONASS) the GG Surveyor automatically uses
only those measurements for which it has corrections. If GG Surveyor has no
differential corrections, it automatically uses all available healthy satellites, from both
constellations, to compute a position. If one satellite system is shut down or jammed,
or if satellites become unhealthy (generating incorrect data), the GG Surveyor
automatically uses the satellites which are operating correctly based on the signal-to-
noise ratio.
Table A.3 lists the expected accuracies in various operating configurations.
*Differential GPS accuracy is affected by the radio data rate. If the data rate is slow,
SA causes errors to grow while the corrections are being transmitted. Figure A.1
shows actual 95% accuracy measured in tests with DGPS and DGLONASS.
The graph shows how position precision decays as the age of corrections increases.
For each particular age, 95% of the position errors sampled were less than or equal to
the value on the graph. Approximately 400 positions were sampled for each age.
Table A.3: Accuracy as a Function of Constellation
Available Constellation
GG Surveyor Mode
Typical (50%)
Accuracy* at
Radio Data Rate
of 1200 bps
95%
Accuracy at
Radio Data Rate
of 1200 bps
Differential GPS &
Differential GLONASS
D(GPS+GLONASS)
35 cm
75 cm
GPS & Differential
GLONASS
DGLONASS
50 cm
1 m
GLONASS &
Differential GPS
DGPS
40 cm
90 cm
GPS & GLONASS
GPS & GLONASS
7 m
16 m
GLONASS
GLONASS
8 m
20 m
GPS
GPS
25 m
100 m
Содержание GG Surveyor
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