 |
| Titel |
VEM on VERITAS - Retrieval of global infrared surface emissivity maps of Venus and expectable retrieval uncertainties |
| VerfasserIn |
David Kappel, Gabriele Arnold, Rainer Haus, Jörn Helbert, Suzanne Smrekar, Scott Hensley |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127675
|
| Publikation (Nr.) |
 EGU/EGU2016-7578.pdf |
|
|
|
|
|
| Zusammenfassung |
| Even though Venus is in many respects the most Earth-like planet we know today, its surface
composition and geology are not well understood yet. The major obstacle is the extremely
dense, hot, and opaque atmosphere that complicates both in situ measurements and infrared
remote sensing, the wavelength range of the latter often being the range of choice
due to its coverage of many spectral properties diagnostic to the surface material’s
composition and texture. Thermal emissions of the hot surface depend on surface
temperature and on spectral surface emissivity. As this emitted radiation wells upward, it
is strongly attenuated through absorption and multiple scattering by the gaseous
and particulate components of the dense atmosphere, and it is superimposed by
thermal atmospheric emissions. While surface information this way carried to space is
completely lost in the scattered sunlight on the dayside, a few narrow atmospheric
transparency windows around 1 µm allow the sounding of the surface with nightside
measurements.
The successfully completed VEX (’Venus Express’) mission, although not dedicated to
surface science, enabled a first glimpse at much of the southern hemisphere’s surface through
the nightside spectral transparency windows covered by VIRTIS-M-IR (’Visible and InfraRed
Thermal Imaging Spectrometer, Mapping channel in the IR’, 1.0–5.1 µm). Two
complementary approaches, a fast semi-empiric technique on the one hand, and
a more fundamental but resource-intensive method based on a fully regularized
Bayesian multi-spectrum retrieval algorithm in combination with a detailed radiative
transfer simulation program on the other hand, were both successfully applied to
derive surface emissivity data maps. Both methods suffered from lack of spatial
coverage and a small SNR as well as from surface topography maps not sufficiently
accurate for the definition of suitable boundary conditions for surface emissivity
retrieval.
The recently proposed VERITAS mission (’Venus Emissivity, Radio Science, InSAR,
Topography, and Spectroscopy’) comprises two instruments, VEM (’Venus Emissivity
Mapper’) and VISAR (’Venus Interferometric Synthetic Aperture Radar’). This mission will
yield a vastly improved data basis with respect to both high SNR Venus nightside radiance
measurements at all transparency windows around 1 µm as well as topography
maps. The new data will enable the derivation of much more complete and reliable
global surface emissivity maps that are required to answer fundamental geologic
questions.
Here, we discuss the selection of the wavelength ranges covered by the spectral filters of
VEM as well as improved estimates of expectable emissivity retrieval errors based on this
selection. For this purpose, the locations of the relevant spectral transparency windows are
studied with detailed line-by-line radiative transfer simulations in dependence on different
spectral line databases. Recent work on VIRTIS-M-IR/VEX measurements indicated the
presence of interferences due to ever-varying atmospheric parameters that cannot be
derived from radiance measurements with limited spectral information content to be a
dominant source of surface emissivity retrieval errors. This work is carried over to the
configuration of VEM, and the retrieval pipeline is optimized to minimize such
errors.
A portion of this work was performed at the Jet Propulsion Laboratory, California Institute of
Technology under a contract with NASA. |
|
|
|
|
|
|