Retrieval of temperature and tangent altitude pointing from limb emission spectra recorded from space by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

Abstract

[1] Retrieval of abundances of atmospheric species from limb infrared emission spectra requires accurate knowledge of the pointing of the instrument in terms of elevation, as well as temperature and pressure profiles. An optimal estimation-based method is presented to infer these quantities from measured spectra. The successful and efficient joint retrieval of these largely correlated quantities depends strongly on the proper selection of the retrieval space, the selection of spectral microwindows, and the choice of reasonable constraints which force the solution to be stable. The proposed strategy was applied to limb emission spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the Envisat research satellite in order to validate the instrument pointing information based on the satellite's orbit and attitude control system which uses star tracker information as a reference. Both systematic and periodic pointing calibration errors were detected, which meanwhile have been corrected to a major part. Furthermore, occasional pitch jumps were detected, which could be assigned to parameter uploads to the satellite's orbit and attitude control system. It has been shown that in general, it is justified to assume local thermodynamic equilibrium below 60 km for these purposes. The retrieval method presented has been proven to be suitable for independent monitoring of MIPAS line-of-sight pointing.

Validation of revised methane and nitrous oxide profiles from MIPAS–ENVISAT

“…To examine the bias between the instruments, the difference (both absolute and relative) of the mean profiles was calculated. Also the standard error for the mean (absolute) difference has been derived to estimate the significance of the bias (von Clarmann, 2006).…”

“…Retrievals of temperature and its horizontal gradient, vertical pointing of the line of sight and many trace gases are conducted with the research data processor developed at the Institute of Meteorology and Climate Research in cooperation with Instituto de Astrofísica de Andalucía (CSIC) (von Clarmann et al, 2003). Earlier versions of the retrieval of CH 4 and N 2 O with this processor for the full-resolution period were described by Glatthor et al (2005), and for the reduced-resolution period by von Clarmann et al (2009).…”

“…Earlier versions of the retrieval of CH 4 and N 2 O with this processor for the full-resolution period were described by Glatthor et al (2005), and for the reduced-resolution period by von Clarmann et al (2009). The retrieval setup of the latest data versions V5R_CH4_224, V5R_CH4_225, V5R_N2O_224, V5R_N2O_225, V5H_CH4_21 and V5H_N2O_21 can be found in Plieninger et al (2015).…”

“…This serves to smooth the retrieved profile, instead of pulling it towards the a priori profile itself (von Clarmann et al, 2009). For CH 4 there are additional diagonal elements in the regularisation matrix for altitudes at 70 km and above (these are altitudes above the highest tangent altitude), where the profile is hence pulled towards zero.…”

MIPAS: an instrument for atmospheric and climate research

“…Moore, 2006) or continuum parameters (e.g. von Clarmann et al, 2003a). Work on many species is on-going but essentially considerable success is being achieved at these low altitudes (see Sect.…”