Global Positioning System Reference
In-Depth Information
3
2.5
2
1.5
1
Each data point represents results of one
upload scenario test case using recorded
GPS data from 1996
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
Average uploads/SV/day
Figure 3.20
MCS uploads versus navigation accuracy. ( From: [27]. 1997 IONS. Reprinted with
permission.)
backup capabilities to support satellite abnormalities.) NGA will provide additional
monitoring stations for the MCS with 15-minute smoothed and 1.5-second raw
pseudorange and carrier phase measurements from Ashtech geodetic-quality receiv-
ers. These smoothed and raw measurements will be used in the CS Kalman filter and
L-band monitor [12] processing, respectively. Once operational, the CS Kalman fil-
ter zero-age-of-data URE will be reduced approximately by one-half [6, 28] and the
L-band monitor visibility coverage will be increased from 1.5 monitor stations/sat-
ellite to 3 to 4 monitor stations/satellite. The combined Air Force and NGA monitor
station network is shown in Figure 3.21.
The L-AII upgrade includes several model improvements to the MCS process-
ing. The existing and planned model updates are summarized in Table 3.6.
Various U.S. government agencies, research laboratories, and the international
GPS community have developed improved GPS models over the past 20 years. These
L-AII model updates of geopotential, station-tide displacement, and Earth orienta-
tion parameters enable the MCS processing to be compliant with the conventions of
the IERS [29]. The recently developed JPL solar pressure model improves the satellite
ephemeris dynamic modeling with the inclusion of Y -axis,
β
-dependent force, where
β
is the angle between the Sun-Earth line and the satellite orbital plane. The
Neill/Saastamoinen model improves tropospheric modeling at low elevations.
The AEP upgrade replaces the MCS mainframe with a distributed Sun worksta-
tion configuration. The AEP upgrade extends beyond the L-AII upgrade to include
an integrated suite of commercial off-the-shelf products and an improved graphical
user interface. The AEP update is an object-oriented software design using TCP/IP
communication protocols across workstations connected by a 1-GB Ethernet local
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