The Atmospheric Remote Sensing and Climate System (ARSCliSys) Research Group was founded in January 1996 by Gottfried Kirchengast after successful initial research activities in the field of atmospheric sounding by radio occultation which had been started in 1994.

The group, in year 2005 comprising more than twelve members, is engaged in the field of Earth Observation from space, with emphasis on advancing the scientific exploitation of modern spaceborne atmospheric remote sensing techniques and on using them for climate monitoring and research as well as weather studies.

In atmospheric remote sensing research, a first main topic is advancement of the Global Navigation Satellite System (GNSS) based radio occultation technique, which has the potential to sense the atmospheric temperature and humidity fields with an unique combination of global coverage, high vertical resolution and accuracy, long-term stability, and all-weather capability. Among other significant contributions to the field, the Group is leading the development of the so-called End-to-end GNSS Occultation Performance Simulator (EGOPS), a software for integrated simulation of all relevant aspects of GNSS occultation science and related mission analysis. Besides being intensely used inhouse for many studies, EGOPS is now employed by more than twenty research institutes and industrial companies in Europe and worldwide.
A second main topic is the complementary utilization of advanced spaceborne spectroradiometric IR/MW sounding techniques, again for high resolution sounding of temperature and humidity fields. A first major development in this field was an advanced physical-statistical hybrid algorithm for retrieval of humidity profiles from passive downlooking MW sounder data. Another major recent development was an innovative algorithm for the retrieval of high-quality temperature and humidity profiles from realistically simulated high-resolution IR spectra of the IR Atmospheric Sounding Interferometer (IASI) planned to be flown on the European METOP satellites (METOP-1 launch: 2005).
A third most recent main topic is research in absorptive occultation techniques (stellar, solar, and LEO-LEO occultation), which can provide information on atmospheric temperature, ozone, and humidity profiles. This is highly complementary to the information in refractive occultation data provided by GNSS radio occultation. One main driver of this work is participation in the validation and exploitation of data from the recently started European environmental research satellite ENVISAT (launch: March 2002), where the sensor GOMOS (Global Ozone Monitoring by Occultation of Stars) is of particular interest. Another main driver is the leading involvement in the ESA Atmosphere and Climate Explorer (ACE+) satellite mission, which was recently, in May 2002, selected by ESA as its top-priority future Earth Explorer Opportunity Mission.

Climate system research topics of key interest include the analysis of naturally and anthropogenically influenced change in the atmosphere's thermal, moisture, and ozone structure (from intra- and interannual variability to interdecadal trends), improvement of climate models and climate forcing inputs via global observational constraints, and climate change detection and attribution. Regarding the latter two research endeavors, the primary interest is to explore and unleash the full potential of the "self-calibration" property of both refractive and absorptive occultation data.
One main already quite advanced study in this field is concerned with the utility of GNSS occultation data for climate change monitoring. More precisely speaking, the primary aim is to rigorously assess the long-term temperature trend detection capability of a small GNSS occultation observing system. The study is carried out in form of a climate observing system simulation experiment over the 25 years from 2001 to 2025, and results from the recently completed performance analysis phase are encouraging for the evaluation of the full 25 year climatology.
Another more recently started project deals with optimal fusion of the occultation data and advanced infrared sounder data into GCM fields in order to obtain coherent global monthly analyses of temperature, humidity, and ozone. These will in turn be used to address the climate change topics noted above.

Methodological interests behind include advanced physical and statistical modeling and innovative utilization of inverse theory, empirical regression theory, and data fusion/assimilation theory. Such concepts and the associated methodologies are employed for optimal estimation of key parameters and their uncertainties in complex deterministic-stochastic systems such as the atmosphere based on indirect measurement data. In the future they will also be used in the setup of climate change detection and attribution schemes.

The outlined research involves use of data of several different satellite missions/sensors (e.g., MicroLab/GPSMet, DMSP/SSM-T1,T2) and strong engagement in very recent and upcoming highly innovative missions/sensors such as CHAMP/GPS, ENVISAT/GOMOS-MIPAS, METOP/GRAS-IASI, and ACE+/AGRAS-CALLS. Furthermore, GCM data such as high-resolution weather analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) and climate simulations from the ECHAM4/5 climate model of the MPI for Meteorology, Hamburg/Germany, are involved on a routine basis.

More detailed information on the activities of the ARSCliSys group can be found in this book chapter (October 2000) written by G. Kirchengast. It contains from its section 4 onwards a fair overview on the group's past research and planned future research. (Note: Minor parts of the chapter - some quoted text pieces - are in German.)

An overview on the main research programme/project lines can be found in this recent summary (pdf/1MB) (October 2002) of ARSCliSys research aims and activities.

More information is found below, where research activities have been categorized into several main programme/project lines. The partitioning is based on scientific rationale rather than on a per-funded-project splitting. For each research area a brief summary is available (more than this for the first line ACE+). Furthermore, some recent presentations are enclosed (pdf files; get Acrobat Reader if needed), which provide more detailed insight into currently on-going research.