Other
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........14w&link_type=abstract
Ph.D. Thesis Massachusetts Inst. of Tech., Cambridge.
Other
1
Emissivity, Permittivity, Radiometers, Venus (Planet), Venus Surface, Dielectrics, Elevation, Magellan Spacecraft (Nasa), Monte Carlo Method, Radiance, Thermal Emission
Scientific paper
Observations performed by the Magellan radiometer experiment have confirmed previous findings that a few regions on Venus, primarily at higher elevations, possess unexpectedly low values of radiothermal emissivity, occasionally reaching as low as 0.3. Values of emissivity below 0.7 occur over about 1.5 percent of the surface, and are associated with several types of features, including highlands, volcanoes, tectonically uplifted terrain, and impact craters. There is a strong correlation of low emissivity and high elevation, but rather than decreasing gradually with elevation, the emissivity drops rapidly in a small altitude range above a certain 'critical radius'. The altitude at which the change in emissive properties occurs varies from feature to feature; on average, it lies at a planetary radius of about 6054 km. Notable exceptions to the association of low emissivity and high elevation exist; for example, Lakshmi Planum, Maat Mons, and the summits of many volcanoes display high emissivities at high elevations, while in some impact craters and plains areas we find low emissivities at low elevations. Two possible explanations for low emissivities have been advanced: (1) emission from a highly reflective single interface between the atmosphere and a surface material having a bulk dielectric constant of order 80 ('high-dielectric' model); and (2) emission from the surface of a low-loss soil having a more usual permittivity (of order 2) which contains subsurface scatterers composed of ordinary rock materials ('volume scattering' model). Theoretical results and Monte Carlo simulations are used to show that the previously proposed volume scattering model cannot account for the observed emissivities; however, scattering from a material with very low loss (loss factor of order 10-3 or less) containing subsurface voids could produce the observed results. Consideration of the two models in light of the Magellan observations leads us to believe that the low emissivities on Venus result from the creation of a high-dielectic material by surface-atmosphere interaction, probably a loaded dielectric containing a conductive mineral.
No associations
LandOfFree
A study of areas of low radio-thermal emissivity on Venus 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 A study of areas of low radio-thermal emissivity on Venus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A study of areas of low radio-thermal emissivity on Venus will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-939728