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Retrieval of Surface Emissivity in a Venus Coordinate Patch as Parameter Common to Repeated Measurements by VIRTIS/VEX

Kappel, David and Arnold, Gabriele and Haus, Rainer (2012) Retrieval of Surface Emissivity in a Venus Coordinate Patch as Parameter Common to Repeated Measurements by VIRTIS/VEX. In: Geophysical Research Abstracts, 14, p. 9708. EGU General Assembly 2012, 22.-27. April 2012, Vienna, Austria.

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Official URL: http://meetingorganizer.copernicus.org/EGU2012/EGU2012-9708.pdf

Abstract

ESA’s planetary probe Venus Express has now been orbiting Venus for six years. It carries the most powerful remote sensing suite ever flown to the planet. The Infrared Mapping channel of the Venus Infrared Thermal Imaging Spectrometer, VIRTIS-M-IR, performs radiation measurements between 1 - 5 µm at a spectral sampling of 9.5 nm. Each exposure yields a frame of 432 spectral bands and 256 spatial samples. A number of consecutive exposures forms a spectrally resolved two dimensional image of a target. In order to extract atmospheric and surface parameters from measurements, a line-by-line radiative transfer simulation model computes the expected observable radiance in dependence on these parameters as well as on instrumental parameters. It considers absorption, emission, and multiple scattering by gaseous and particulate constituents. An associated retrieval algorithm iteratively varies the parameters until the residual between measurements and simulations in terms of a certain cost function is locally minimized. As this is an ill-posed problem, it is regularized by taking into account a priori mean values and variances of the parameters as well as measurement and simulation errors. This is accomplished by using a Bayesian formulation of the cost function and basically acts to rule out subsidiary solutions with unlikely parameter values. Nevertheless, the retrievals are still affected by other subsidiary solutions. To further regularize the retrieval, multiple spectra can be fitted simultaneously by defining extended measurement and parameter spaces as the concatenations of the corresponding single spectrum spaces. This allows the introduction of additional a priori data defining the expected spatial-temporal correlations between parameters to be retrieved from contiguous measurements. This approach in effect rules out subsidiary solutions with unlikely spatial-temporal parameter distributions and also allows for the retrieval of parameters common to several spectra. By treating surface emissivity at a certain surface coordinate bin as parameter common to repeated measurements covering this bin, the retrieval uncertainty can be greatly decreased in comparison to isolated retrievals from individual measurements. When several bins that sample a patch on the surface are analyzed at once, a local surface emissivity map can be determined. This map thus results from rigorous radiative transfer and retrieval, where each single measurement is parameterized by a consistent set of atmospheric, surface, and instrumental parameters. The combined parameter set of all analyzed measurements respects all available a priori data and the measurement/simulation error distributions and does not neglect the context between adjacent measurements. The declaration of surface emissivity as a parameter common to certain measurements from the outset represents an approach that is more rigorous as compared to a simple averaging of individual retrievals which implicitly allows inconsistent parameter sets. The results for a selected surface area in the vicinity of Idunn Mons are discussed exemplarily.

Item URL in elib:https://elib.dlr.de/78190/
Document Type:Conference or Workshop Item (Poster)
Title:Retrieval of Surface Emissivity in a Venus Coordinate Patch as Parameter Common to Repeated Measurements by VIRTIS/VEX
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Kappel, DavidDavid.Kappel (at) dlr.deUNSPECIFIED
Arnold, GabrieleGabriele.Arnold (at) dlr.deUNSPECIFIED
Haus, RainerWestfälische Wilhelms-Universität MünsterUNSPECIFIED
Date:24 April 2012
Journal or Publication Title:Geophysical Research Abstracts
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Volume:14
Page Range:p. 9708
Status:Published
Keywords:VIRTIS, Venus Express, Surface emissivity, Retrieval
Event Title:EGU General Assembly 2012
Event Location:Vienna, Austria
Event Type:international Conference
Event Dates:22.-27. April 2012
Organizer:European Geosciences Union
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Exploration des Sonnensystems
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research
Deposited By: Kappel, David
Deposited On:09 Nov 2012 09:23
Last Modified:31 Jul 2019 19:38

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