Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31d..02m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P31D-02
Other
[5450] Planetary Sciences: Solid Surface Planets / Orbital And Rotational Dynamics, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6295] Planetary Sciences: Solar System Objects / Venus
Scientific paper
Venus Express is an ESA spacecraft orbiting Venus since April 2006. The instrument VIRTIS acquires multispectral images in the range from 0.2 to 5 μm wavelength. An analysis of VIRTIS images of the atmospheric windows at 1.02, 1.10 and 1.18 μm shows evidence for variation of surface emissivity on the southern hemisphere. The emissivity of rock or soil in the NIR range is sensitive to its mineral composition and grain size distribution. The surface is subject to weathering, which may alter both mineral composition and grain sizes. Therefore the surface emissivity has the potential to give evidence of original rock composition as well as weathering processes and their effective duration. Mapping the emissivity might give clues about rock forming processes or surface age. Bands 0, 8, 17 and 30 of VIRTIS -M IR image cubes, accessible at the ESA planetary science archive PSA (http://www.rssd.esa.int/psa), are corrected for stray-sunlight and limb-darkening to retrieve flux of radiation emitted through the windows. Cloud transmittance is determined from 1.31 μm and applied to 1.02, 1.10 and 1.18 μm while accounting for multiple reflections between lower atmosphere and clouds. The remaining surface thermal emission is highly correlated with Magellan altimetry. Owing to the greenhouse climate the surface temperature can assumed to be constant temporally albeit steadily decreasing with surface elevation. The residual of emission after removal of the global trend with Magellan altimetry is positively correlated with emissivity variation and is used as basis for surface studies. The signal of emissivity is small compared to the signal of surface temperature represented by Magellan altimetry. While the nominal vertical error of Magellan data of 50 m is sufficient for NIR emissivity estimation there are still some uncertainties due to the topography data. In an initial estimates a bias of higher apparent emissivity to the western flanks of topographic elevations was found. This is might be indicative of an offset of longitude of 0.15° between the VIRTIS images and the Magellan data set. Estimates of the period of rotation of Venus from different radar observations disagree outside of their formal errors. The possible error in angular velocity accumulated over the 16 years between Magellan and Venus Express might account for the apparent offset. Comparison of VIRTIS and Magellan data does not provide unambiguous evidence on the rotation period since an actual bias of NIR emissivity or surface temperature with respect to direction of slope can not be ruled out yet. On the other side there is no compelling argument for such a bias and we will use a shift in coordinates for surface emissivity studies, effectively assuming a period of rotation 0.0014 % longer than the value currently recommended by the IAU.
Helbert Jérôme
Mueller N. T.
No associations
LandOfFree
On Combining Radar Altimetry and Near-Infrared Imaging for an Estimate of Venus Surface Emissivity does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with On Combining Radar Altimetry and Near-Infrared Imaging for an Estimate of Venus Surface Emissivity, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and On Combining Radar Altimetry and Near-Infrared Imaging for an Estimate of Venus Surface Emissivity will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1770661