GPS System Segments - Understanding GPS: Principles and Applications - page 102

England

Alaska

South Korea

USNO
Cape Canaveral

Bahrain

Schriever

Kwajalein

Hawaii

Ecuador

Diego Garcia

Ascension

Argentina South Africa

Australia

New Zealand

Air Force tracking stations
NGA tracking stations

Figure 3.21 Combined Air Force and NGA monitor station network.

Table 3.6 Existing and Planned Model Upgrades

Model Existing MCS Capability [15, 20] Planned MCS Upgrade

Geopotential model WGS84 (8 × 8) gravitational EGM 96 (12 × 12) gravitational

harmonics harmonics [29]

Station tide displacement Solid tide displacement accounting

for lunar and solar vertical
component only

IERS 2003, including vertical and
horizontal components [29]

Earth orientation parameters No zonal or diurnal/semidiurnal

tidal compensation

Restoration of zonal tides and
application of diurnal/semidiurnal
tidal corrections [29]

Solar radiation pressure model Rockwell Rock42 model for Block

II/IIA and Lockheed Martin Lookup
model for IIR

JPL empirically derived solar pressure
model [30]

Troposphere model Hopfield/Black model Neill/Saastamoinen model [31, 32]

area network (LAN). The AEP distributed architecture maintains the MCS opera-
tional data in an Oracle database (with a standby failover strategy).
The AEP upgrade provides the infrastructure for incremental MCS improve-
ments, including support for the IIF satellites and the modernized signals (see Sec-
tions 3.2.3.7 and 4.5, respectively). Regarding the modernized signals, an
alternative NAV Data message representation will be deployed with additional
parameters and reduced quantization errors. Representative curve fit errors associ-
ated with the modernized NAV Data message are shown in Figure 3.22. For 3-hour
utilization intervals, three performance metrics are depicted: RMS URE, the maxi-
mum URE, and the RSS position errors. For the June-July 2000 period and across
all satellites, the constellation RMS-URE, Max-URE, and Max-RSS errors were
0.543, 0.943, and 3.56 cm (RMS), respectively. A comparison with the results of
Figure 3.19 shows that the modernized signals curve fit errors will be significantly
reduced.