Global Positioning System Reference
In-Depth Information
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TABLE 1.1
( Continued )
1996
Presidential Decision Directive, first U.S. GPS policy
Vice president announces second GPS civil signal at 1227.60 MHz
JPL's automated GPS data analysis service via Internet
1998
Vice president announces GPS modernization initiative and third civil GPS signal
at 1176.45 MHz
IGDG (Internet-based global differential GPS) at JPL
1999
Selective availability set to zero
GPS JPO begins modifications to IIR-M and IIF satellites
2000
[5]
GPS surveying firm (Collins and Leick, 1985). Also in 1984, GPS was used at Stan-
ford University for a high-precision GPS engineering survey to support construction
for extending the Stanford Linear Accelerator (SLAC). Terrestrial observations (an-
gles and distances) were combined with GPS vectors. The Stanford project yielded
a truly millimeter-accurate GPS network, thus demonstrating, among other things,
the high quality of the Macrometer antenna. This accuracy could be verified through
comparison with the alignment laser at the accelerator, which reproduces a straight
line within one-tenth of a millimeter (Ruland and Leick, 1985). Therefore, by the
middle of 1984, 1-2 ppm GPS surveying had been demonstrated beyond any doubt.
No visibility was required between the stations. Data processing could be done on
a microcomputer. Hands-on experience was sufficient to acquire most of the skills
needed to process the data—i.e., first-order geodetic network densification suddenly
became within the capability of individual surveyors.
President Reagan offered GPS free of charge for civilian aircraft navigation in
1983 once the system became fully operational. This announcement was made after
the Soviet downing of the Korean Air flight 007 over the Korea Eastern Sea. This
announcement can be viewed as the beginning of sharing arrangements of GPS for
military and civilian users.
Engelis et al. (1985) computed accurate geoid undulation differences for the Eifel
network, demonstrating how GPS results can be combined with orthometric heights,
as well as what it takes to carry out such combinations accurately. New receivers
became available—e.g., the dual-frequency P-code receiver TI-4100 from Texas
Instruments—which was developed with the support of several federal agencies. Ladd
et al. (1985) reported on a survey using codeless dual-frequency receivers and claimed
1 ppm in all three components of a vector in as little as 15 minutes of observation time.
Thus, the move toward rapid static surveying had begun. Around 1985, kinematic
GPS became available (Remondi, 1985). Kinematic GPS refers to ambiguity-fixed
solutions that yield centimeter (and better) relative accuracy for a moving antenna.
The only constraint on the path of the moving antenna is visibility of the same four
(at least) satellites at both receivers. Remondi introduced the antenna swapping tech-
nique for the rapid initialization of ambiguities. Antenna swapping made kinematic
positioning in surveying more efficient.
Lin
0.5
——
No
PgE
[5]
 
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