Planetary atmosphere observation analysis

Abstract:

We report a wide-ranging study of Titans surface temperatures by analysis of the Moons outgoing radiance through a spectral window in the thermal infrared at 19 μm (530 cm -1) characterized by lower atmospheric opacity. We begin by modeling Cassini Composite Infrared Spectrometer (CIRS) far infrared spectra collected in the period 20042010, using a radiative transfer forward model combined with a non-linear optimal estimation inversion method. At low-latitudes, we agree with the HASI near-surface temperature of about 94 K at 10°S (Fulchignoni et al, 2005). We find a systematic decrease from the equator toward the poles, hemispherically asymmetric, of ∼1 K at 60° south and ∼3 K at 60° north, in general agreement with a previous analysis of CIRS data (Jennings et al, 2009), and with Voyager results from the previous northern winter. Subdividing the available database, corresponding to about one Titan season, into 3 consecutive periods, small seasonal changes of up to 2 K at 60°N became noticeable in the results. In addition, clear evidence of diurnal variations of the surface temperatures near the equator are observed for the first time: we find a trend of slowly increasing temperature from the morning to the early afternoon and a faster decrease during the night. The diurnal change is ∼1.5 K, in agreement with model predictions for a surface with a thermal inertia between 300 and 600 J m -2 s -1/2 K -1. These results provide important constraints on coupled surfaceatmosphere models of Titans meteorology and atmospheric dynamic. © 2011 Elsevier Ltd. All rights reserved.

Abstract:

We present new laboratory thermal infrared emissivity spectra of the major silicate minerals identified on the Moon measured under lunar environmental conditions and evaluate their application to lunar remote sensing data sets. Thermal infrared spectral changes between ambient and lunar environmental conditions are characterized for the first time over the 400∼1700 cm -1 (6-25 m) spectral range for a fine-particulate mineral suite including plagioclase (albite and anorthite), pyroxene (enstatite and augite), and olivine (forsterite). The lunar environment introduces observable effects in thermal infrared emissivity spectra of fine particulate minerals, which include: (1) a shift in the Christiansen feature (CF) position to higher wave numbers (shorter wavelengths), (2) an increase in the overall spectral contrast, and (3) decreases in the spectral contrast of the reststrahlen bands and transparency features. Our new measurements demonstrate the high sensitivity of thermal infrared emissivity spectra to environmental conditions under which they are measured and provide important constraints for interpreting new thermal infrared data sets of the Moon, including the Diviner Lunar Radiometer Experiment onboard NASA's Lunar Reconnaissance Orbiter. Full resolution laboratory mineral spectra convolved to Diviner's three spectral channels show that spectral shape, CF position and band ratios can be used to distinguish between individual mineral groups and lunar lithologies. The integration of the thermal infrared CF position with near infrared spectral parameters allows for robust mineralogical identifications and provides a framework for future integrations of data sets across two different wavelength regimes. Copyright 2012 by the American Geophysical Union.