THE INTERNATIONAL GPS SERVICE |
The
history and development of the International GPS Service (IGS)
demonstrates
the unique capability of international geodetic groups and
agencies to work
successfully together for a common goal.
The primary motivation for the establishment of the IGS was the recognition in 1989 that the most demanding GPS users, the community of scientists involved in the measurement of crustal motion, were experiencing difficulties interpreting the results of GPS field campaigns because there were: (a) no global reference system, and (b) no GPS satellite orbit ephemerides accurate enough.
The relative positioning accuracy requirement for such users is of the order of 0.01 parts per million, about one hundred times the accuracy of standard GPS surveying (section 2.4.4). As discussed in section 6.2.1, in order to satisfy high accuracy users, a range of observation and modelling biases have to be accounted for. Two of these biases are the "satellite ephemeris bias" and the "reference station bias". The IGS was therefore established to support users that had to address these two biases in particular.
A description of the IGS, its functions and products, the background history and present status, can be found in a series of articles in ZUMBERGE et al (1995) and subsequent Annual Reports. Another useful information source is the IGS Web page (section 3.4.2).
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© Chris Rizos, SNAP-UNSW, 1999