Pointing and temperature retrieval from millimeter-submillimeter limb soundings

• Passive microwave limb sounding instruments like the Millimeter-Wave Atmospheric Sounder (MAS) or the Microwave Limb Sounder (MLS) observe dedicated oxygen lines for the derivation of temperature and pointing information, since these quantities are essential for the quality of the retrieval of the trace gas mixing ratio. Emission lines of oxygen are chosen because the volume mixing ratio (VMR) profile is known. In this paper, we demonstrate the capabilities of a new and innovative method by means of which accurate temperature and pointing information can be gathered from other strong spectral features like ozone lines, without including accurate knowledge of the VMR profile of these species. For this purpose, retrievals from two observation bands with a bandwidth of about 10 GHz each, one including an oxygen line, have been compared. A full error analysis was performed with respect to critical instrument and model parameters, such as uncertainties in the antenna pattern, calibration uncertainties, random pointing error, baseline ripples, baseline discontinuities, and spectroscopic parameters. The applied inversion algorithm was the optimal estimation method. For the selected scenario and instrumental specifications we find that the retrieval of a pointing offset and the atmospheric temperature profile can be achieved with a good accuracy. The retrieval precision of the pointing offset is better than 24 m. The retrieval precision of the temperature profile is better than 2 K for altitudes ranging from 10 to 40 km. Systematic errors (due to model parameter uncertainties) are somewhat larger than these purely statistical errors. Investigations carried out for different atmospheric states or different instrumental specifications show similar results.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Rymd- och flygteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Aerospace Engineering (hsv//eng)

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