Submitted abstracts (19 April 2004)

R. Biancale (1), J.-M. Lemoine (1), S. Loyer (1), L. Soudarin (2), A-M. Gontier (3),
D. Coulot(4,5), P. Berio (5), P. Exertier (5), N. Capitaine (3), D. Gambis (3),
J. Chapront (3), G. Francou (3)
1. CNES/GRGS 2. CLS 3. Paris Observatory/SYRTE 4. IGN 5.OCA/GEMINI
Comparison of DORIS products vs. other geodetic techniques
in the framework of IERS combination research centers

X. Chavet (1), J.-J. Valette (1), M. Feissel-Vernier (2,3)
1. CLS 2. Paris Observatory 3. IGN
Analysis of geocenter time series derived from SLR, GPS and DORIS (Poster)

Using various time series of sets of station coordinates derived from
satellite geodetic observations, we describe the motion of the Earth's
geocenter by the time series of the origin of the individual data sets
in a common reference frame. The goal of the analysis of these time
series is to extract and compare various components such as trend,
seasonal and irregular components. In addition to the comparative
analysis of the individual signals, a noise analysis of the series is
performed. The geodetic techniques involved are DORIS, SLR and GPS, and
the respective time intervals are monthly, weekly and daily.

E. Doornbos (1), P. Willis (2,3)
1. DEOS 2. IGN 3. JPL
Analysis of DORIS residuals from multiple satellites and POD

Residuals of tracking data are an important by-product of precise satellite
orbit computations. They contain information about the performance of the
tracking system and the models used in the orbit computation and can be used
to identify possible problems. DORIS residual RMS values per pass have been
made available by various POD centres and for various DORIS satellites. This
data has been visualized and compared, in order to look for possible
improvements in future DORIS data processing.

Dilbar Fazilova
Astronomical Institute of Uzbekistan
Establishment of the Uzbekistan space network reference point (Poster)

The use of astronomical and classical geodetic points is one of the ways
of building regional space network reference point. So, former Kitab
latitude station can be used for establishing Uzbekistan space network
reference point. Investigation of Kitab kinematical and dynamical
parameters is the objective of this project. Kitab GPS and DORIS station
coordinates were used as space network reference point. Helmert and
Molodensky transformation models were used to conduct initial
investigation of connection between ITRF and SK-42 (Krasovsky ellipsoid)
reference systems. Differences between the above coordinates are
X=-22.56m, Y=125.03 m, Z=87.20m and B=6.83m, L=-71.36m, H=-28.83 m.
RMS of transformed coordinates is X42=0.015 m, Y42=0.043 m, Z42=0.032m.
To define the elements of the network orientation with respect to WGS
or ITRF and to calculate the parameters of connection between them and
local terrestrial system SC-42 comprehensive model was used along with
astrometric and space data.

M. Feissel-Vernier
Paris Observatory and IGN
The Analysis Coordination information website

The Analysis Coordination website includes or gives access to a number of
informations that are expected to be useful for currently operational
analysis centers as well as newcomers. The topics involved are general
information, satellite models, ground network, stations, observations
and products content and availability, data centers organisation, reports,
etc. The existing content and extension plans will be described.

M. Feissel-Vernier
Paris Observatory and IGN
The station events file (Poster)

The file was prepared to
centralize under machine readable form the information on the events that
occur and occured at the DORIS stations. The file currently includes eight
different types of informations, as follows.
- Start date of observations, taken from the SIMB DorisMails or sitelogs
- End date of observations, taken from the SIMB DorisMails or sitelogs
- Warnings taken from the SIMB DorisMails or sitelogs
- Data to be deleted (present source: P. Willis)
- Breaks in station history, e.g. after an earthquake
- Coordinate changes between two stations in the same site.
- A priori coordinates when not available in ITRF2000 (e.g. new beacons)
- A priori velocities when not available in ITRF2000
New information types could be added if requested. It is planned to
maintain the record of the consensus knowledge of the analysts about the
stations problems.

M. Feissel-Vernier (1,2), K. Le Bail (2)
1. Paris Observatory 2. IGN
Search for changes in the STJB station behaviour, a case study (poster)

Taking the case of the St John station, several approaches to detect
changes in the time behaviour of station coordinates are presented.
Changes in bias, drift and spectral content are considered.

M. Feissel-Vernier (1,2), J.-J. Valette (3)
1. Paris Observatory 2. IGN 3. CLS
Validating time series of TRFs via their Helmert parameters

Time series of unconstrained terrestrial reference frames are produced, at
weekly or monthly intervals, by IDS Analysis Centers. For being used in
geodetic or geophysical studies, they have to be uniformly referred to a
standard terrestrial reference frame, usually ITRF2000. This can be done
by several methods. By-products of this unification step are the time
series of their Helmert parameters describing the positions of the TRF
origin, their scales and orientations. The various signatures of these
time series, in terms of seasonal, interannual and long term components,
and the comparisons between signatures of different series, can be used to
validate the solutions. Some examples of such analyses will be shown.

M. Feissel-Vernier (1,2), L. Soudarin (3)
1. Paris Observatory 2. IGN 3. CLS
Influence of the gravity field model on the orbital reference frames

As a part of the 2003 IDS Analysis Campaign, daily DORIS satellite orbits
were computed over the Oct-Dec 2002 time span, using five different
gravity field models. The changes of orbital reference frames with respect
to the orbits referred to GGM01C are described by series of Helmert
parameters (origin coordinates, scale and orientaion). The signal and
noise contents of these time series are investigated.

K. Le Bail
Long term stability of DORIS and GPS station coordinates. Some examples

Using time series of station coordinates over 1993-2003 derived from DORIS or GPS
observations, we investigate the measurement error spectrum by the Allan variance
estimator. In order to isolate the measurement error, it is necessary to eliminate
the geophysical signal. We test two ways for this elimination, 1. by taking off
a linear trend and 2. by considering the series of differences between the original
series, which contain only the sum of the two series noises (three corner hat method).
We show detailed results of the two methods for a few stations. Results of the
three corner hat method for about 35 colocated DORIS-GPS stations are shown on
the poster presentation "Study of the time stability of global parameters:
Comparison between GPS and DORIS terrestrial reference frames".

K. Le Bail (1), M. Feissel-Vernier (1, 2)
1. IGN 2. Paris Observatory
Study of the time stability of global parameters
Comparison between GPS and DORIS terrestrial reference frames (Poster)

ITRF2000 is the international terrestrial reference frame constructed
from GPS, VLBI, SLR and DORIS time series of station coordinates from
different analysis centres. These are combined together with weights
depending on the technique precision. The goal of this study is to
find appropriate weight according to statistics parameters. We use
time series of station coordinates of GPS and DORIS collocations
from different analysis centres of the two techniques. From each
terrestrial reference frame created, we try to determine a
relationship between statistics, techniques and analysis strategies
studying the Helmert parameters.

F.G. Lemoine (1), R. Govind (2), S.B. Luthcke (1), N.P. Zelensky (3)
1. NASA/GSFC/LTP 2. Geoscience Australia 3. Raytheon ITSS
Gravity Model Comparisons and Orbit Determination Analyses with DORIS data

With the launch of CHAMP and GRACE, we have entered a new era of space
geodesy. New geopotential models are available that provide global and
uniform coverage for the first time. The new models that have been
developed since the launch of CHAMP in July 2000, and the launch of the
GRACE satellites in March 2002, include the suite of EIGEN models
developed from CHAMP data by the GFZ and the GRGS, the models developed
by the GRACE team at UT/CSR, GFZ including GGM01s, GGM01C, EIGEN-GRACE01S,
EIGEN02-GRACE, as well as the PGS7777B, and PGS7779E models developed by
the GSFC from CHAMP and other satellite data. We propose to compare these
models performing OD computations on the JASON, TOPEX/Poseidon, and Envisat
satellites using only DORIS data. The comparisons can include RMS of fit
to the data, orbit overlap and consistency comparisons. In addition we will
use the SLR tracking of the these satellites as an 'independent' gauge of
the POD quality, where we may look specifically at the high elevation SLR
RMS. We will compare the performance of the new models with the older
generation models including EGM96, GRIM5-C1, JGM3 and TEG4.

The availability of a multiplicity of tracking systems on the JASON
spacecraft, including GPS and SLR data allows us to compute
reduced dynamic orbits that have achieved the 1 cm radial orbit accuracy
goal set for this mission [Luthcke et al., 2003]. We can use these
independent GPS+SLR orbits as a basis from which to 'independently'
characterize the DORIS system performance. We will review the results
from this analyses, with a view to obtaining further insight into
the performance of the JASON DORIS system wrt to the South Atlantic anomaly.

B. Meisel, D. Angermann, M. Krügel
Comparison and combination of Doris data with other space techniques

This presentation deals with comparing and combining DORIS data with
the space techniques VLBI, SLR and GPS. A main focus thereby is on the
terrestrial reference frame. We compare local tie information from
terrestrial measurements with results from a multi-year TRF combination.
Furthermore we investigate the time series and the covariance
information of station positions and datum parameters (geocenter and
scale) and present results of a TRF combination from weekly normal
equations including an estimation of seasonal signals.

C. Noll (1), E. Gaulué (2)
IDS Data Center Update

The IDS data centers archive both DORIS data and products generated
from these data by the IDS analysis centers. This presentation will
review the structure of the archives, data and product availability,and
address open issues. A summary of data access will also be presented.

M. Otten
Performance monitoring of Envisat DORIS doppler data and orbit solution

The Navigation office at the European Space Operation Centre (ESOC) has
been actively involved in the calibration and validation of the Envisat
DORIS doppler data and the precise orbit solution throughout the mission
lifetime. The current activities, performed during the operational phase
of the mission, consist of monitoring the overall performance of the
Envisat DORIS doppler data and the MOE and POE orbit solution from CNES.
The results of these activities are reported bi-weekly on our website.
This presentation will give an overview of the activities performed
during the last two years.

M. Parrot, F. Li
On the TEC determination from the ionospheric DORIS products

This paper is related to the use of the ionospheric DORIS products available
on the CDDIS web server in order to obtain the TEC (Total Electron Content)
parameter. It will describe the method we use to recover the TEC and the
problems we have. Comparisons of the results are done with the IRI2001 model.
This work is done in the frame of the DEMETER project to be launched on
June 29, 2004. The main scientific objective of DEMETER is to study the
ionospheric perturbations in relation with the seismic activity. TEC is an
important ionospheric parameter and during the mission we intend to consider
all possible measurements related to the status of the ionosphere.

J. Ries
Jason-1 orbit determination with DORIS and SLR:
An alternative approach for accommodating the SAA effect

The DORIS system on Jason-1 is subject to dramatic perturbations in
the vicinity of the South Atlantic Anomaly (SAA). An alternative
approach to accommodating the impact on the DORIS tracking is tested
based on 1) tight editing to identify passes which are significantly
upset by the SAA, and 2) estimating a correction to the resulting
frequency drift model that is incorrect for the remaining unaffected
DORIS data. Since this effect comes through the model, it is common
to all unaffected data, so only a single parameter is necessary to
add to the orbit solution problem. The result is that a large portion
of the DORIS data is edited, but what remains continues to fit at the
same level as the earlier cycles when the SAA effect was more benign.
Further, there is no systematic beacon height drift apparent in the
DORIS residuals, which is present if the erroneous drift model is not

L. Soudarin (1), J.-F. Crétaux (2)
Recent DORIS analysis at LEGOS/CLS analysis center


L. Soudarin (CLS)
The Central Bureau information system

Within the IDS,the information is provided through the web and ftp sites
of the Central Bureau , the Data Centers and the Analysis Coordination,
depending on the kind of information. Day-to-day news of general interest
are given to the DORIS community by the DORIS mail service. This
presentation will review the organization of the information.

L. Soudarin (1), H. Capdeville (1), R. Biancale (2)
1. CLS 2. CNES
Modeling the DORIS tropospheric corrections with the help of ECMWF models

Doris beacons are systematically associated with meteorological sensors which
automatically deliver along with the Doris signal pressure, temperature and
humidity data on site. These data are then used in orbit processing to compute
the propagation delay in the troposphere for each measurement. This delay is
generally issued from a model (for instance CNET), and is based on a zenithal
correction plus an elevation function, both depending on the state of the
troposphere. However this approach remains quite inaccurate compared with the
Doris measure quality. That's why precise orbit modelling of the DORIS
satellites require the adjustment of many non dynamical parameters such as
frequency offset and tropospheric zenithal bias per pass, increasing thereby
the degree of freedom of the inverse system in the orbit adjustment
On the other hand, the global knowledge of the troposphere has improved a lot and
meteorological centres like ECMWF provide now in high resolution 6h-grids over
60 levels pressure, temperature and humidity data which, once integrated
vertically, gives directly the zenithal delay at the resolution of the grids
which is commonly used in altimetry.The topics of the presented study is to
adapt these tropospheric gridded data to the DORIS measurements and to assess
them in orbit computation and in comparison with other methods.

P. Stepanek (1,2), U. Hugentobler (3)
1. Geod. Obs. Pecny 2. Czech T.U. 3. AIUB
Implementation of DORIS data analysis into the Bernese GPS software

The Bernese GPS software has been developed at the Astronomical Institute,
University of Bern. In a joint project with IGN the capability for analyzing
DORIS measurements is currently implemented into a test version of the
software. The analysis technique for processing DORIS observations follows
a GPS-like approach. Initial tests using TOPEX data from CDDIS in format
2.0 were performed; the processing of observations in format 2.1 is
currently implemented. The final version of the software may be used for
the treatment of DORIS data in the framework of the IDS. The Research
Institute of Geodesy, Topography and Cartography in Zdiby (Czech Republic)
is planning to use the software in the envisaged Czech analysis center.

S.K. Tatevian, S.P. Kuzin
Institute of Astronomy, RAS, Moscow.
Geocenter variations derived from 10 years of GPS and Doris data

Time series of geocenter variations with respect to the ITRF00 have been
obtained from two sources: the solutions from DORIS and GPS data for the
same ten-year period of time. Data analysis was performed with the GIPSY/OASIS2
software. Daily solutions of coordinates of the IGS core stations and about
of 50 DORIS stations are combined into weekly solutions and transformed to
a well defined ITRF2000 with the use of 7 parameters of Helmert transformation.
Three estimated translations parameters and scale factor provide information
on variations of geocenter positions. The two time series (for GPS and DORIS data)
have been analysed separately and compared. The harmonic and regression analyses
have been applied in order to estimate a constant term, linear trend, semi-annual
and annual amplitudes and phases. Additionally to the annual and semiannual
signals with amplitudes 4.1-11.5 mm, several other more shorter periods (a
fortnight and of one to four months) were found in both time series. It must
be noted that the amplitudes of some short-periodic signals are comparable with
the amplitudes of semiannual signals. Besides, the secular trend of the geocenter
motion with a velocity of a few mm per year was found. An investigation of
the observed time series of geocenter motion is important for improvement
of geophysical models and for establishing a more

J.-J. Valette (1), M. Feissel-Vernier (2,3)
1. CLS 2. Paris Observatory 3. IGN
IDS analysis campaigns: present status

The analysis of the IDS products have been initiated in 2002 with coordinates
time series of the DORIS station network and with Earth orientation parameters.
The participation, the methodology and a summary of the results are presented.
With the recent coming of the new Earth Gravity field models derived from the
GRACE mission, a 2003 campaign has been proposed with a focus on a three months
dataset. The present state of the ongoing work is shown. The opportunities
for the future validation, comparison and combination of the solutions on a
regularly basis are discussed.

P. Willis (1,2), J.-F. Crétaux (3)
1. IGN 2. JPL 3. LEGOS
DORIS Data Analysis Strategies. Position Paper

Since the official start of the International DORIS Service (IDS), some
solutions are now available from different group on a regular basis. The goal
of this paper is to summarize the availability of current IDS products, to
analyze the technical difficulties currently experienced and to propose some
recommendations on how to improve the current situation. More specifically,
some actions will be proposed to improve the current product generation and
validation scheme. Ways to attract new groups to participate will also be
investigated. Some discussion will also be done to extend necessary information
to be able to process the DORIS data more efficiently. Finally, a preliminary
analysis will be conducted on procedure to select new models and the need to do
so (gravity field, correction of the South Anomaly effect on Jason on-board
oscillator,...). In each case, we propose a recommendation to be discussed openly
at the IDS Plenary Session.

P. Willis (1,2), Y. Bar-Sever (2), S. Desai (2)
1. IGN 2. JPL
DORIS data processing at the IGN/JPL Analysis Center

The IGN/JPL Analysis Center is currently contributing to the International
DORIS Service by submitting regularly DORIS weekly sinex solutions and their
derived products (geocenter and Earth Rotation Parameter time series). Since
the official start of the IDS, all DORIS data have been reprocessed using a
GRACE-derived gravity field (GGM01C), showing a better internal consistency of
the results as well as indications of better accuracy, when compared with
estimates from external sources such as GPS and local tie information. A lot of
efforts have been put in automating the DORIS data processing at JPL leading
since December 2003 to a fully automated distribution of IGN/JPL IDS products
in a very timely manner. Data are now processed on the day they are received at
CDDIS data center. IDS products are then generated and also delivered on the
same day at CDDIS data center without any human intervention at JPL. This
center is now fully operational and ready to participate in the IERS Pilot
campaign, complying with the tighter delivery schedule for DORIS products. This
presentation will focus on the current contributions of the IGN/JPL DORIS
Analysis Center to the IDS. It will also present the currently achieved
accuracy of these products using now 5 DORIS satellites (still excluding Jason
data), showing improvement when using an extended DORIS satellite
constellation. It will also present some new research areas presently under
consideration, such DORIS satellites antenna patterns evaluation.

E. I. Yagudina
IAA RAS, St. Petersburg
The status of the processing of DORIS observations in IAA RAS

Testing of a software developed in IAA for processing DORIS system
observations is outlined. Calculations are made in the frame of the
programming complex ERA used in IAA for processing SLR and VLBI
observations. Due to absence of the available model of the shape of
DORIS satellites to be used for modelling the dynamical effects
of the light pressure and atmosphere, the method of short arcs is
applied. In this method the maximal data span of observations
could not be taken more than two days; as the result large correlations
of coordinates of stations with clock errors restrict the achieved
accuracy of these coordinates to 10-25 cm, notwithstanding
the good estimation of the clock errors with Kalman filter applied,
and the satisfactory fit to observations (rms is about 1.2 mm/sec).
The usage of exact satellite model is necessary.