Planetary atmosphere observation analysis

Abstract:

The retrieval of surface composition from IR measurements of airless bodies requires a model capable of computing the significant thermal gradients present in the top few hundred microns of the regolith. In this study we introduce a model which reproduces most of the features found in controlled experiments made in the simulated lunar environment emission chamber (SLEEC). Although the model presented here is forced by a lower boundary held at a fixed temperature, we conclude that a similar algorithm driven by solar illumination may be used as a forward model to retrieve composition, particle size and effective thermal conductivity from IR measurements of airless bodies. Copyright 2011 by the American Geophysical Union.

Abstract:

Nightside infrared limb spectra of the Venus upper atmosphere, obtained by Venus Express VIRTIS, show strong scattering of thermal radiation. This scattering of upward-going radiation into the line-of-sight is dominant below 82.5. km even at a wavelength of 5 μm, which is indicative of relatively large particles. We show that 1 μm-sized sulfuric acid particles (also known as mode 2 particles) provide a good fit to the VIRTIS limb data at high altitudes. We retrieve vertical profiles of the mode 2 number density between 75 and 90. km at two latitude ranges: 20-30°N and 47-50°N. Between 20 and 30°N, scattering by mode 2 particles is the main source of radiance for altitudes between 80 and 85. km. Above altitudes of 85. km smaller particles can also be used to fit the spectra. Between 47 and 50°N mode 2 number densities are generally lower than between 20 and 30°N and the profiles show more variability. This is consistent with the 47-50° latitude region being at the boundary between the low latitudes and high latitudes, with the latter showing lower cloud tops and higher ultraviolet brightness (Titov, D.V., Taylor, F.W., Svedhem, H., Ignatiev, N.I., Markiewicz, W.J., Piccioni, G., Drossart, P. [2008]. Nature 456, 620-623). © 2010 Elsevier Inc.