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to this resolution).
Precise single point positioning developed by Zumberge et al. is used extensively today.
Consistency of orbit and clink information is crucial for this technique, The required consistency
level (of millimeters) is much easier to achieve if the same software package is used to produce
the global products (orbits and clocks) AND the coordinates using the single point positioning
technique. It was/is most encouraging to see that already today, thanks to an essential upgrading
of the combination technique, the consistency level for the combined IGS products is not far
away from the best possible consistency level that may be reached (using one and the same
software). It seems feasible that sub-centimeter point-positioning using IGS products should be
possible in the very near future.
Other recommendations dealt with the “densification project”. It was recommended that
deadlines in compliance with other deadlines in the IGS are used, that EOP information is
included by all analysis centers in the GNAAC solutions, and that all discrepancies/errors in the
RINEX files are removed.
Also, the minimal requirements (perfomnance-wise) to become an IGS Analysis Center were
reviewed (and probably clearly defined for the first time). As this recommendation was
extensively discussed and modified at the workshop, it is advisable to wait for the final version
of this position paper.
There were other interesting contributions in the first session. Jim Zumberge presented a
technique at JPL to produce in an efficient way high-rate GPS clocks, Wolfgang Soehne from
GFZ presented the GFZ procedures developed for the same purpose. Jim Ray gave a short status
report of the IGS/BIPM project: the call for participation was issued in January, the next phase
will consist of evaluating the proposals received in spring 1998.
Topic 2: Orbit Prediction and Rapid Products (Session Chair: Tim Springer, John Dow)
Tomas Martin Mur (ESA), Tim Springer (CODE) and Yoaz Bar Sever (JPL) reviewed the
procedures for “Orbit Prediction and Rapid Products” in the position paper for topic 2. With the
increasing demand for close to real-time products this issue becomes more and more important.
It came out very clearly that data availability is THE critical issue. Global coverage is far more
important than the number of stations (provided a minimum number of about 30 stations is
available).
The paper also reviewed the prediction techniques used by individual IGS Analysis Centers and
in the combination. Usually, IGS predictions are much better than broadcast orbits (the former,
when compared to the IGS final orbits are of about 30-50 accuracy (extrapolation over 2 days),
the latter are of 2-3 meter accuracy). There are exceptions, however, which are not always
predictable. Two measures may improve the reliability of IGS predicted orbits: (a) reduction
of the delay of data availability (see primary recommendation below), (b) reduction of the
number of “unknown” parameters for prediction process.
New orbit models developed by Yoaz Bar-Sever at JPL and by Tim Springer at CODE axe
promising in area (b). Only improved data transmission may help in area (a): Therefore, the frost
arid probably the primary recommendation of the position paper asks the operational and global
data centers to give highest priority to the delivery of stations outside Europe and North America
(!). This does not mean, of course, that data from Europe and North America are not important;
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