Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43d1709g&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43D-1709
Physics
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
Thermal inertia is an important derived variable from thermal infrared remote sensing, since it depends on physical properties of the studied surface, including density (ρ), heat capacity (c), and bulk thermal conductivity (λ). For example, due to its stronger heat capacity, water has a greater thermal inertia compared to rocks, and thus, moisture on Earth can be derived from thermal inertia. On Mars, thermal conductivity is believed to be strongly linked with grainsize. Consequently, thermal inertia is widely used for the study of surface processes. Physically, thermal inertia is defined as the ratio of thermal flux variation (ΔΦ) to surface temperature variation (ΔT), on a sinusoidal forcing, and can be re-write as follow : I=ΔΦ/ΔT=√(λ.ρ.c) To retrieve thermal inertia from thermal infrared pictures, a model is needed : the variation of surface temperature during the day is modelled for different values of thermal inertia and then compared to remote sensing temperature. Additional parameters, like atmospheric dust concentration or sun angles are set to predict the brightness temperature, as seen by the satellite. These models do not account well for infrapixellar roughness. However, surface geometry is responsible of a few effects : - Shadowing of part of the surface makes the sun incoming flux spatially and temporally variable. - The interreflexion between two opposite surface makes the local flux weaker. Consequently, a rough surface is heated during a shorter time, compared with a smooth one, but the effect is strongly non-linear. In this study, we designed a radiative and conductive code to test these effects, taking into account a 2D roughness surface state. By modelling the heat fluxes on several geometries, we retrieved the surface temperature evolution, compared to smooth geometry. Here, the key parameters are the geometry, the height of the roughness and the physical parameters of the soil (emissivity, albedo, thermal conductivity and heat capacity). These studies leads to a correction factor, strongly dependant on the geometry of the roughness. We applied our results to the Mars ejecta of impact craters, to watch out the uncertainties on thermal inertia determination, due to infrapixellar roughness.
Allemand Pascal
Delacourt Christophe
Gaudin D.
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