Section 1.1 is involved in research and development activities in the following topics
GNSS Atmosphere Sounding
Ground-based GPS data from a global and from regional networks are analyzed in near-real time. Resulting data products (zenith and slant total delay, integrated water vapor) are provided for the operational assimilation to regional weather models and for several scientific investigations. GFZ also supports temporary atmospheric measuring campaigns (e.g. CSIP: 2006; COPS:2007; WMO-LUAMI:2008 or HYMEX 2012) by the installation, operation and data analysis of GPS ground stations. GPS slant data from the German network (around 400 stations in analysis as of Dec. 2012) are used to reconstruct 3D water vapor distributions.
A second pillar of GFZ expertise in atmospheric sounding is the satellite based GPS radio occultation (RO) technique for precise vertical atmospheric sounding on a global scale. The GFZ spectrum here covers activities related to data processing (CHAMP, GRACE, TerraSAR-X, TanDEM-X, Metop, COSMIC), but also the application of the RO data for various scientific investigations at GFZ. An example for the data processing is the provision of GPS RO data from GRACE-A and TerraSAR-X in near-real time for the continuous assimilation to improve weather forecasts at different national and international weather centers. Scientific investigations focus to the exploitation of the RO data for climatological investigations of tropopause and gravity wave characteristics, but also to detailed analysis of the occurrence of ionospheric irregularities. Additional investigations are related to the design of new satellite missions using GPS remote sensing techniques.
The main part of the GFZ activities in GNSS atmosphere sounding is performed within the Helmholtz Research field "Earth and Environment", programme "Atmosphere and Climate" in close cooperation with KIT and FZ Jülich.
GNSS (GPS, Galileo, GLONASS, BeiDou) reflectometry belongs to the class of bistatic radar systems which can be used as a tool for Earth remote sensing. In a bistatic configuration transmitter and receiver reside at different locations. The receiver passively uses emitted signals of sources of opportunity. Beside the direct line-of-sight signals a GPS reflectometry receiver can potentially use all GPS signals that are reflected from the Earth's surface. As the GPS signals are transmitted continuously, the receiver can continuously receive the signal, allowing for continuous measurements of the reflecting surface.
The transmitted GPS signal interacts with the reflecting surface and some part of the signal is reflected and can be registered at the receiver. In comparison to the directly received signal the reflected signal arrives at the receiver with a certain delay. From the associated path length difference and the knowledge about transmitter and receiver position the altimetric height of the specular reflection point can be calculated from geometric relations. Observations of this kind belong to the field of GNSS altimetry.
As the surface roughness of a reflecting sea surface scatters the energy pattern of the reflected signal, significant wave height and wind speed can be derived from the temporal development (the waveform) of the received reflected signal. Observations of this kind belong to the field of GNSS scatterometry.
One of the relevant new aspects introduced by the bistatic character of GNSS reflectometry is the dependence of its capabilities on the measurement geometry. Different measurement geometries occur due to different positions of the transmitting GNSS satellites at the same time. Thus, the receiver can acquire reflector height and surface roughness information, e.g., sea state, from different reflection point locations simultaneously.
GNSS Analysis Centers and Services
This research area includes activities within the IGS (International GNSS Service), development and improvement of GNSS data analysis software and contributions to the European Global Navigation Satellite System Galileo.
GFZ has been developing its GNSS analysis software EPOS for decades and is maintaining the software according to the latest standards and developments. GFZ is also very active in developing new algorithms in order to improve the quality of the IGS products and to enhance the capability of GNSS data processing.
Since 2007, GFZ has been developing its GNSS real-time software package, EPOS-RT. The software is designed not only to run in network mode which is now used for geohazard monitoring (earthquake, tsunami, volcano, landslide), but also to be able to estimate orbit and clock corrections to provide services to users with single-frequency receivers in precise point positioning mode (IGS Real-Time Pilot Project). The above-mentioned functions can be demonstrated now and further improvement on the robustness and accuracy of the software is in progress.
The Galileo Geodetic Service Provider (GGSP) was developed until 2009 with the target to support the In-Orbit-Validation for the Galileo System starting in 2011. This service will be offered to be part of the final Galileo system.
GFZ is operating a global GNSS station network (currently ~30 stations) since the early 1990s to support scientific research activities like precise satellite clock & orbit determination, radio occultation measurements and crustal dynamics. Additionally operational services for the European satellite system Galileo and various scientific campaigns are supported.
Links to the projects under this topic:
Geodetic and astronomical VLBI
- Sorry, information on this topic is presently only available in German language. -