Satellite Orbits - ashtech GG Surveyor Reference Manual

Changes are planned for the GLONASS frequency plan:
•
•
•
Any or all of these changes in frequency will have no effect on the GG Surveyor
GPS+GLONASS receiver, because the capability to handle any of the carrier number
assignments is built in, and the satellite almanac always tells the receiver which
assignment to use for each satellite.
The satellite ephemerides are like a high-precision almanac, they tell the receiver
precisely where the satellite is. Each satellite (both GPS and GLONASS) transmits its
own ephemerides. The GPS satellites provide their positions in terms of the WGS- 84
(World Geodetic System, 1984) while the GLONASS satellites provide positions in
the PZ-90 reference system (sometimes called PE-90 Parameters of the Earth, 1990 or
E90). The GG Surveyor translates the two systems into a single user-selectable
reference system. The default is WGS- 84, and by default, the GG Surveyor converts
GLONASS satellite positions into WGS-84 coordinates and computes positions in
WGS-84 coordinates.

Satellite orbits

The orbits of GPS and GLONASS are similar. GPS satellites orbit in 6 planes, 4
satellites per plane. GLONASS uses 3 planes, 8 satellites per plane. The GLONASS
inclination is slightly higher (64.8°) than GPS (55°). The orbits of both systems are
circular, and with similar radii.
Geoid Model
The GG Surveyor uses the OSU-91 geoid model. Grid size is 5 x 5 degrees, and the
interpolation technique is similar to the GPS ICS algorithm. Expected accuracy when
the actual position is on a grid point is 0.5 to 0.6 meters, in accordance with the OSU-
91 specification. Expected accuracy when the actual position is halfway between grid
points is better than 8 meters.
A-4
Stage 1—Present to 1998 -The carrier numbers will be assigned in such a
way as to avoid the frequencies in the band 1610.6-1613.8 MHz used in
Radio Astronomy. This means the carrier number assignments K= 16, 17,
18, 19, 20 will not be used. To compensate for the lost frequencies, identical
frequencies will be used for two satellites on opposite sides of the earth.
Stage 2—1998 to 2005 - The next Generation of GLONASS-M satellites
will use the carrier number assignments 1 through 12.
Stage 3—beyond 2005 - The GLONASS-M satellites will use the carrier
number assignments (-7 through +4). Carriers 5 and 6 will be used for
interaction with the ground control segment.
GG Surveyor GPS+GLONASS Reference Manual