The NAVSTAR Global Positioning System (GPS) has the capability to compute accurate receiver positions for a variety of space and Earth-based applications. An Earth-based application such as hazardous waste storage site deformation monitoring requires highly accurate, reliable, and routinely available positioning. These positioning needs motivated the development of a fiber optics GPS observational network (FOGON). The FOGON network would operate by placing GPS antennas at known geodetic locations and transmitting the received analog satellite signals along a phase stable fiber optic link to a central processing site. This central site would synchronize the data acquisition of the network and enable single difference operation, which is the strongest possible GPS observable data type. This paper presents the results of a hardware demonstration of the analog transmission of GPS spread spectrum signals over a 4.17-km fiber optic link and through an optical attenuator, with minimal degradation to GPS receiver operation.>

The authors discuss the development of space geodetic systems-important tools in an attempt to understand the evolution of the atmosphere and oceans-particularly as they pertain to the problem of global warming. The science of time and frequency metrology has made possible the development of space geodetic systems that are being applied to the high accuracy tracking of new space-based instruments. These new instrument sets and methodologies have been designed to be appropriate for many years to decades of operation in order to measure the open ocean circulation and sea level as an indicator of global warming and will be a vital means for assessing the effectiveness of future remedial actions. The issues of time and frequency are tied into all of these space geodetic techniques, from the cesium and rubidium oscillators aboard global positioning system (GPS) satellites, to the epoch time and time interval measurements of satellite laser ranging (SLR) and hydrogen maser references used in very long baseline interferometry (VLBI).>