GPS Surveying in an Urban Environment Under AS

Iain R. Webster, John M. Nolan, Sergei A. Gourevitch, and Xinhua Qin

Abstract:	With 24 working satellites in orbit, the GPS constellation is now capable of providing worldwide coverage for many positioning and navigation applications. Advances in receiver technology and processing algorithms have increased the cost-etfectiveness of using GPS for surveying in many areas. Some of the most ditkrlt environments for the GPS surveyor are urban area!% High-rise buildings and other overhead features can cause the GPS signals to be frequently obstructed. In addition, since observation windows are often shorter than normal, signal acquisition times also need to be short in order to provide suflicient observations for reliable results. Furthermore, and perhaps more significantly, this type of environment is extremely conducive to multipath effects. Finally, DOD policy states that Anti Spoofing, or AS, (where the P-code is encrypted to prevent civilian use) will be turned on once the system becomes operational This paper describes tests carried out in a typical urban environment, with Ashtech’s Z-12 receiver, using Z-Tracking’” to give an indication of conditions during periods when Anti-Spoofing (AS) will be turned on.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	595 - 603
Cite this article:	Webster, Iain R., Nolan, John M., Gourevitch, Sergei A., Qin, Xinhua, "GPS Surveying in an Urban Environment Under AS," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 595-603.
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