Atmospheric and surface retrievals in the Mars polar regions from the Thermal Emission Spectrometer measurements

Abstract

[1] Retrievals of atmospheric temperatures, surface emissivities, and dust opacities in the Mars polar regions from the Thermal Emission Spectrometer (TES) spectra are presented. The retrievals correspond to two types of spectra, characterized by small and large band depths BD 25 in the 25-mm band of solid CO 2 . These two types of spectra have previously been identified with locations covered by slab ice and fluffy CO 2 frost, respectively. Above the first atmospheric scale height, there is a correlation between the degree of saturation in the retrieved atmospheric temperatures and the two types of surface, with the high BD 25 spectra (''cold spots'') showing larger supersaturations around 1 mbar. This supports the hypothesis that cold spots correspond to locations with potential or actual atmospheric precipitation. Furthermore, the retrieved temperature profiles exhibit a warming above 1 mbar (15 km), which appears real even when the limited number of independent pieces of information from the measurement ($3) and coarse vertical resolution of the TES instrument above 15 km are considered. The spectral shape of the retrieved surface emissivities in the cold spot locations is consistent with modeling results attributing high BD 25 to porosity. For the low BD 25 spectra, the retrieved emissivities are spectrally flat but significantly less than unity (0.8-0.9). The cause of these spectrally uniform deviations from blackbody behavior (which are not supported by modeling) remains to be investigated, with a noticeable reduction in the deviation from the blackbody behavior achieved through a zero-radiance-level correction to the TES spectra available from the Planetary Data System.

Impact of assimilation window length on diurnal features in a Mars atmospheric analysis

“…TES temperature errors are estimated to be around 3 K, with higher errors in polar regions and near the surface (Eluszkiewicz et al, 2008). Systematic errors can also vary from orbit-to-orbit.…”

Assessment of Mars atmospheric temperature retrievals from the Thermal Emission Spectrometer radiances

“…1). Although this study is restricted to temperatures, we note that the M1R algorithm also retrieves dust, ice opacity, and surface emissivity (Eluszkiewicz et al, 2008). In the context of this study, which focuses on temperature retrievals, these additional retrievals act as ''corrections'' (consistent with radiances and the assumed noise level) and are not validated.…”

“…where y 0 is the observed radiance, S e is the error covariance of the observation, F(x) is the calculated radiance, x prior is the mean a priori, and S prior the a priori covariance matrix around the mean (Rodgers, 2000;Eluszkiewicz et al, 2008). The specification of these Gaussian statistics for the prior differs from the PDS algorithm where a single first guess was assigned based on the radiance (Conrath et al, 2000).…”

“…The M1R algorithm was originally developed for terrestrial use, but has been adapted to the martian atmosphere and previously used to retrieve polar temperature profiles (Eluszkiewicz et al, 2008). It employs a forward model based on the OSS method in which channel radiances are approximated as linear combinations of radiances computed at selected monochromatic points .…”

“…The M1R algorithm outputs averaging kernels that improve data assimilation (Hoffman et al, 2011). While the averaging kernels are not discussed in this paper, the reader is referred to Rodgers (2000) for the underlying theory and Eluszkiewicz et al (2008) for an example. 3.…”