You are here:

1. Home
2. Work Packages
3. WP3000

Generation of Consistent Observation Time Series of the Individual Space Techniques for Geodetic-Geophysical Parameters (GIUB)

The space geodetic observation techniques SLR, VLBI, GPS, DORIS, altimetry, etc. provide the basis for the realization of a global geodetic-geophysical observing system. Thus, all the global observations of these techniques will be homogeneously and consistently reprocessed within work package WP3000. Thereby much care is taken to adapt uniform standards, models and parameterizations. The definition and implementation of these standards are performed in WP3100, which requires the participation of all project partners. The respective tasks are provided in the partial proposals.

Because of the existing very close cooperation between the institutions involved and the work in the framework of the previous GEOTECHNOLOGIEN project (03F0336A, IERS) such a homogenization of the different software packages and a consistent reprocessing can be achieved with a reasonable effort. On the international level such a homogenization is extremely difficult, and in the near future (e.g. in 3 years) it could only be realized to a certain extent, because it requires the overall coordination of many contributing institutions (e.g., analysis centers for the different techniques, combination centers for the intra- and inter-technique combinations).

Together the project partners possess all the required know-how, experiences and software packages to perform a homogeneous and consistent reprocessing of all data series of the different space techniques. Table 1 gives an overview of the time series (SINEX files) for the different space techniques, which will be generated in work packages WP3200 - WP3600. The envisaged time spans for the different techniques range from 4 to 20 years. The results of these work packages provide an optimal basis for the intra- and inter-technique combination in WP4000. In addition to weekly SINEX files, in the work packages WP3200 - WP3500 also daily files are computed, which provide a significantly higher temporal resolution for the resulting time series for geodetic-geophysical parameters.

Table 1: Generation of consistent time series (SINEX-Files)

The redundancy of two institutions and two software packages for each of the major space geodetic techniques is intended and absolutely necessary, since com-parisons within the different international services have clearly shown that therewith software-related problems, erroneous models or strategies can be identified and corrected in an early stage. By means of the redundant time series it is also possible in this project to simulate the existing international data flows, comparisons and combinations and to transfer the refined procedures in the future - or perhaps during this project - to the international services.

For the processing of Low Earth Orbiters (LEOs) such as CHAMP, GRACE and possibly other satellites a combined adjustment of the data of a global GPS and SLR station network together with GPS observations on the LEOs, GPS and SLR observations to the LEOs as well as K-band measurements between the GRACE satellites is performed. Thereby significant contributions for the estimation of the low-degree spherical harmonic coefficients of the gravity field can be expected.

Furthermore satellite altimetry allows to deduce the redistribution of water masses and therewith provides contributions to geocenter variations, the Earth rotation (in terms of OAM), and the temporal variation of the gravity field. For DORIS official weekly solutions are available from the International DORIS Service (IDS). In this case it is difficult to ensure uniform standards. The investigation of refined combination strategies as for example the introduction of low-degree gravity field coefficients or tropospheric parameters are therefore not possible with DORIS at present. In the framework of this project a close cooperation with IGN/JPL (Pascal Willis) is intended to achieve a large agreement concerning the implementation of uniform standards.

Table 2 shows the complete parameter space for a rigorous combination of the different space geodetic observation techniques. Within this project all parameter types that are marked in grey are considered. With the inclusion of quasar coordinates (celestial reference frame), nutation parameters (offsets and rates), Earth rotation parameters with a sub-daily resolution, troposphere parameters and low-degree spherical harmonic coefficients of the Earth's gravity field, this project goes far beyond the combination of station coordinates and Earth rotation parameters currently undertaken by the international services. Thus, many innovative investigations can be performed and new strategies can be tested within this project. Last but not least, for the first time not only geometry and Earth rotation, but also the gravity field - at least the low-degree spherical harmonic coefficients - is included in the combination.

Table 2: Parameters of a rigorous integration/combination

We may expect that during the combination process deficiencies will appear (mainly concerning systematic effects, modeling and parameterization). Therefore, we intend to perform the computations in an iterative way (see dashed lines in Figure 2). All observation time series generated in WP3200 - WP3600 are archived in the data and information system (WP2100) and are consistently used for the research and development tasks performed within the partial projects. Furthermore these data are also available for the international services as significant contribution for extended investigations and combinations on the international level.

Results of Work Package 3000 (German)