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Project name:ACTLIMB - Study of the Performance Envelope of Active Limb Sounding of Planetary Atmospheres
Project leader:Gottfried Kirchengast
Project manager:Susanne Schweitzer
Project team:Gottfried Kirchengast
Susanne Schweitzer
Veronika Proschek
Florian Ladstädter

Staff members at DMI:
Hans-Henrik Benzon
Georg Bergeton Larsen
Kent Baekgaard Lauritsen
Stig Syndergaard

Staff members at CNIT:
Fabrizio Cuccoli
Luca Facheris
Enrica Martini

Staff members at DLR:
Claudia Emde

Staff members at FMI:
Esa J. Kallio
Viktoria Sofieva
Johanna Tamminen

Consulting Experts:
Michael Gorbunov (Institute of Amtospheric Physics, Moscow, Russia)
Joachim Horwath (Institute of Communications and Navigation, DLR, Oberpfaffenhofen, Germany)
Partners:Danish Meteorological Institute (DMI), Copenhagen, Denmark
National Inter-University Consortium for Telecommunications (CNIT), Florence, Italy
Institute of Atmospheric Physics, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
Finish Meteorological Institute (FMI), Helsinki, Finland
Sponsor:European Space Agency (ESA)



The purpose of the ACTLIMB project is to assess the capabilities and performance of the active limb sounding (also termed occultation) technique, exploiting radio, microwave (MW) and shortwave infrared (SWIR) signals. In doing so, ACTLIMB focuses on the Earth’s upper troposphere and lower stratosphere (UTLS), the region where terrestrial occultation techniques are most promising for sounding atmospheric climate, chemistry, and dynamics with unique quality and comprehensiveness (towards end of project some scaling of results to planetary atmospheres, focus Venus and Mars, will be done). Some attention is also paid to the free lower troposphere (down to the top of boundary layer), regarding MW retrieval performance in presence of clouds and turbulence, and the upper stratosphere, regarding the performance in this fairly rarefied gas up to the stratopause.

Furthermore, given that the radio occultation technique (e.g., using GPS radio signals) was already proven in a series of satellite missions, ACTLIMB focuses on the techniques of MW occultation (MWO; cm- and mm-wave signals) and IR laser occultation (ILO; SWIR signals), where no demonstration mission has been undertaken yet and where combining ILO with MWO is novel and was only recently first proposed by the link\{ACCURATE mission proposal to ESA\}. ACTLIMB aims to contribute in particular improved understanding of the performance of this ACCURATE-type combined MWO and ILO mission concept, complemented at the end by scaling the performance to planetary atmospheres (Venus and Mars).

ACTLIMB supports these aims by pursuing the following specific objectives:

  •     to review the applications of active radio-MW-IR occultation techniques applied so far or proposed for the future (such as the ACCURATE-type MWO+ILO concept),
  •     to assess the retrieval performance of MW occultation, putting the focus on performance limits in challenging atmospheric conditions (cloudy and turbulent conditions relative to clear-air conditions; and rarefied target species conditions),
  •     to extend the technique to the SWIR domain, putting the focus on combined MWO+ILO and its performance in challenging conditions (cloudy, turbulent, and aerosol-laden conditions relative to clear-air; and rarefied conditions) as well as in joint sounding of thermodynamic and trace species variables,
  •     to assess the performance of the (combined) MWO and ILO methods under non-ideal geometries (foci space-to-ground, space-to-airplane, airplane-to-ground, airplane-to-airplane, ground-to-ground), and the degree to which the non-ideal geometry concepts allow to demonstrate the validity of full occultation geometry implementations,
  •     to identify unifying and differing elements of the various approaches of radio-MW-IR occultation, and to extend and scale the results to planetary atmospheres, and
  •     to develop and enhance in course of the work the corresponding simulation and processing software tools (propagation modeling and retrieval algorithms, especially the End-to-end Generic Occultation Performance Simulation and Processing System EGOPS).

With this work scope the ACTLIMB project also provides necessary and valuable pre-requisite and complementary work to the partly concurrent link\{IRDAS project\}.

Univ.-Prof. Mag. Dr.rer.nat.

Gottfried Kirchengast

Phone:+43 316 380 - 8431

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