Z. Altamimi
TRF and EOP Comparative analysis between DORIS and other
space geodesy techniques

CATREF software, used for ITRF combination, is now upgraded to
include Earth Rotation Parameters. Using CATREF new features
some simultaneous combinations of TRF and EOP provided by
DORIS and other techniques will be evaluated. We focus on
the limitation factors inherent to each technique and to the
combination, such as the current status of the observing
networks, distribution of the collocation sites and their
quality and accuracy of the combined frame parameters.
Some questions related to DORIS contribution to IERS products
(EOP, geocenter motion) will be opened for discussion.        

C. Noll, E. Gaulué
Archive and distribution of DORIS data and products in support of the IDS

The data centers supporting the International DORIS Service (IDS) are 
the primary means of distributing DORIS data and products to the user 
community. This presentation will outline background information, current 
status, and recent developments at the IDS data centers.  The overview 
will also include a review of available data and product types and recent 
changes to the directory structure and file naming conventions adopted 
by the IDS data centers.

L. Soudarin, J.F. Crétaux, J.J. Valette
Contribution of  the new satellites to the positioning performances

With the 'historic' constellation of  the DORIS-carrier satellites 
(Spot-2, -3, -4, Topex/Poseidon), the positioning performances are at 
the one-centimeter level for monthly station solution, and at the 1-mas 
level for the daily Earth pole position. With the three new instruments 
launched recently onboard  Jason-1, Spot-5, and Envisat, we may expect a 
significant improvement of the results, and a decreasing of the time span 
of observations allowing to reach the level of precision obtained until 
today. We present here the results of the analysis of two months of 
data from the six flying satellites (July-August 2002). We will compare 
different combination of constellation that we used to compute station 
coordinate sets and EOP series, and show the precision of monthly and 
weekly solutions.

J.J. Valette, Z. Altamimi, L. Soudarin 
Combination of DORIS TRF

Analysis Campaign for stations coordinates data sets has been led in 2002. 
We will present the Analysis Centres participation and the results obtained 
for comparison and combination of the solutions. We will present the future 
developments among them the extension of the analysis to EOP with CATREF 
software. A useful discussion will focus on what has to be done now 
considering the present products and what will be the best combination 
strategy to get prepared for a DORIS technique combined solution expected 
by IERS.

B. Meisel, D. Angermann
Intra-technique combination at DGFI: some aspects related to DORIS

In the function as ITRS Combination Center and IERS Combination Research Center,
DGFI is strongly involved in the combination of space geodetic observations,
such as VLBI, SLR, GPS and DORIS.
In this presentation I will briefly describe the combination strategy of DGFI.
In this context I will focus on the general methodology for the combination of
solutions of the same technique. Some relevant aspects related to this
intra-technique combination include the reconstruction of unconstrained normal
equation, the relative weighting of individual solutions, the datum definition,
the detection of outliers (reduction of bad stations), etc. With regard to the
issues mentioned above I will present first results related to presently
available DORIS solutions

R. Warnant, L. Morel, S. Stankov, J.-C. Jodogne, H. Nebdi, N. Jakowski.
The use of DORIS as a tool to study the Earth ionosphere.

Space Geodetic techniques based on dual frequency signals have already proven 
their usefulness for the study of the ionosphere and are nowadays widely used 
by the ionosphere community. The so-called “geometric free” combination of 
the measurements made on these dual frequency signals allows to retrieve the 
Total Electron Content which is the integral of the electron concentration along 
the receiver-to-satellite path from the bottom of the ionosphere (about 50 km) up 
to the altitude of the satellite considered. This geodetic technique does not give a 
direct access to the electron concentration which is the most interesting data for 
ionospherists. Nevertheless, the combination of several techniques at the same 
location allows to retrieve more detailed information. The paper illustrates the 
interest of such collocations for ionospheric studies. 
First, the collocation of GPS (altitude 20 000 km) and DORIS (altitude from 800 
to 1 336 km) allows to give information about the integrated electron content of 
the protonosphere (ionised atmosphere above 1 000 km) by simply making the 
difference between GPS and DORIS electron contents. In addition, the 
collocation of GPS, DORIS and an ionosonde allows to retrieve the electron 
concentration profile which could be used to validate ionospheric models. The 
installation of a DORIS beacon at the Geophysical Centre of Dourbes (Belgium) 
would allow to take profit of such a collocation.

P. Willis, Y. Bar-Sever
DORIS time series elaboration with the GOA software : Summary of 
station related problems (1993-2002)

Since 1998, IGN and JPL have been producing in a common effort times 
series of DORIS tracking stations coordinates in the SINEX format. 
Those series are currently easily available at the DORIS data center 
at CDDIS. Besides stations coordinates monitoring for geodetic and 
geophysical applications, such times series are also used for 
geocenter motion investigation and Earth Rotation determination. In a 
first step, we will present the current strategy using the 
Gipsy/Oasis II software, also used for GPS data processing and called 
"free network" approach. We will then present the advantages of such 
a procedure. Finally, we will focus on the numerous problems found in 
the realization of the latest DORIS time series (from 1993 to 2002). 
We will show that several stations present a non-linear movement that 
can be due to several phenomena: antenna physical falls (Ottawa, 
Amsterdam, Thule), Earthquakes (Arequipa, Colombo, Dyonisos, 
Sakhalin, Socorro Is.) or volcano depletion (Soccoro Is.). It is 
important that all DORIS analysis groups adopt the same naming 
conventions when breaks are found in stations coordinates time 
series. Otherwise, combining such different series would create 
systematic errors at the level of a couple of cm. We propose here, 
for discussion, a list of all problems that we found in our latest 
analysis. It would be important that other groups share these 
information and that a common agreement could be found between all 
DORIS analysis groups in the identification of such breaks and in the 
naming of these stations when exchanging SINEX solutions, either 
times series or global position and velocity global solution.

P. Willis, B. Haines, Y. Bar-Sever, L. Young
DORIS/JASON data, what is happening in the South Atlantic Anomaly region?

In December 2001, the JASON satellite has been launched carrying 
on-board an improved DORIS receiver that can record more precise 
DORIS data (multi-channel with a lower instrumental noise). Precise 
orbit determination groups have shown excellent results in comparison 
or in combination with the 2 other tracking techniques on-board the 
satellite (GPS and Laser). However, for geodetic applications some 
abnormal results were found for certain stations coordinates. The 
goal of this paper is to summarize and characterize the different 
problems encountered using the JPL Gipsy/Oasis software on the 
DORIS/JASON data for different type of applications: Precise orbit 
determination, ground tracking station positioning, stations and 
satellites clock frequency determination. We will show that all 
results are related to the crossing of the South Atlantic Anomaly 
region by the JASON satellite and propose a scientific explanation of 
these phenomena. In this region of the world, the satellite clock is 
accelerated, due to the higher density and protons and this can be 
seen in all types of results. The other DORIS satellites seem to be 
less sensitive to this phenomena, probably because the their DORIS 
clock is better shielded or because their clock is less sensitive to 
radiations. We will show that the physical phenomena seems to 
increase at a steady pace, almost at a linear trend, showing a 
saturation of the JASON/DORIS clock. We will propose some ways to 
cope with this physical phenomena for different type of application 
and also show that usual data processing commonly used for other 
DORIS satellite does not work properly.