Simultaneous retrievals of temperature and volume mixing ratio constituents from nonoxygen Odin submillimeter radiometer bands

Abstract

We present the retrieval of temperature and O(3) volume mixing ratio profiles in the middle atmosphere from a single strong O(3) line. We performed the study using simulated limb-sounding measurements in the frame of the submillimeter radiometer (SMR) instrument that will be carried by the Odin satellite that is due to be launched in early 2001. This study is interesting for the Odin SMR data analysis because we first provide additional temperature measurements, and second reduce significantly the O(3) retrieval error that is due to the temperature and pressure uncertainties. Nonlinear retrievals are performed to retrieve the O(3), CO, H(2)O, and temperature profiles simultaneously from the spectral band 576.27-576.67 GHz. The pressure profile is deduced from the hydrostatic equilibrium equation after each iteration. Temperature and O(3) can be retrieved throughout the stratosphere from 15-50 and 20-50 km, respectively, with a vertical resolution of 3 km. The altitude domain corresponds to the parts of the atmosphere where the signal intensity saturates in some spectrometer channels. A total error of 4-6 K has been found in the temperature profile, mainly because of the instrumental thermal noise and to a lesser extent the calibration. The total error in the O(3) profile is 5-10% and is dominated by the O(3) line-broadening parameter. The total error on the retrieved pressure profile is 2-10% because of the errors in calibration and reference pressure.

The Level 2 research product algorithms for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

“…Between 20-50 km, temperature can be retrieved from the optically thick central channels of the strongest O 3 line at 625.371 GHz (Baron et al, 2001). The O 3 VMR profile and line-of-sight angles have distinct signatures on the wings of the spectral line: the line amplitude changes with VMR while the relative width of the line changes with the line-of-sight angle.…”

Observations of the mesospheric semi-annual oscillation (MSAO) in water vapour by Odin/SMR

“…The retrieved altitude resolution is usually about 3 km. The retrieval is done with a non-linear scheme using the Optimal Estimation Method (OEM) (Rodgers, 2000;Baron et al, 2001). The iteration scheme is based on a Newton and Levenberg-Marquardt method (Lautié et al, 2001).…”

Odin/SMR limb observations of stratospheric trace gases: Level 2 processing of ClO, N2O, HNO3, and O3

“…Vertical profiles are retrieved from the spectral measurements of a limb scan by inverting the radiative transfer equation for a non‐scattering atmosphere. Retrieval algorithms based on the Optimal Estimation Method (OEM) [ Rodgers , 1976], a linear inversion method using statistical a priori knowledge of the retrieved parameters for regularization, were developed for the ground segment of Odin/SMR in Sweden and in France [ Baron , 1999; Baron et al , 2001, 2002; Merino et al , 2001, 2002; Lautié et al , 2001; Lautié , 2003; Eriksson et al , 2002, 2005; Urban et al , 2002, 2004a].…”

“…In practice, only the lowest tangent‐views are rejected using this criterion. In the case of bands containing optically thick lines (O 3 and HNO 3 band at 544.6 GHz), temperature information is retrieved simultaneously, in accordance with recommendations from dedicated studies [ Baron et al , 2001; Cailley , 2002]. Moreover, the measurement error is assumed to be 3 K higher than the theoretical noise calculated from the radiometer equation (4.5 K higher for the 544.6‐GHz band), in order to account for baseline artifacts (e.g., offsets, ripples) present in the calibrated spectra (of level 1b, calibration version 4).…”