A summary of GPS development and performance

Because the scope of GPS research and application development is so broad and conducted by researchers all over the globe, it is impossible to give a comprehensive listing. Therefore, merely demonstrates the extraordinarily rapid development of the GPS Solution . GPS made its debut in surveying and geodesy with a big bang. During the summer of 1982, the testing of the Macrometer receiver, developed by C. C. Counselman at M.I.T., verified a GPS surveying accuracy of 1–2 parts per million (ppm) of the station separation. Baselines were measured repeatedly using several hours of observations to study this new surveying technique and to gain initial experience with GPS. During 1983 a thirty (plus)-station first-order network densification in the Eifel region of Germany was observed (Bock et al., 1985). This project was a joint effort by the State Surveying Office of North Rhein-Westfalia, a private U.S. firm, and scientists from M.I.T. In early 1984, the geodetic network densification of Montgomery County (Pennsylvania) was completed. The sole guidance of this project rested with a private  GPS surveying firm (Collins and Leick, 1985). Also in 1984, GPS was used at Stanford University for a high-precision GPS engineering survey to support construction for extending the Stanford Linear Accelerator (SLAC). Terrestrial observations (angles 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 Tracking Devices For People.

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. 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 technique for the rapid initialization of ambiguities. Antenna swapping made kinematic positioning in surveying more efficient. 

Finally, during 1998 and 1999, major decisions were announced regarding the modernization of GPS. In 2000, SA was set to zero as per Presidential Directive. When active, SA entails an intentional falsification of the satellite clock (SA-dither) and of the broadcast satellite ephemeris (SA-epsilon); when active it is effectively an intentional denial to civilian users of the full capability of GPS ( GPS Tracking Device ).

More information at http://www.jimilab.com/ .