Pointing and temperature retrieval from millimeter‐submillimeter limb soundings

Abstract

[1] 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.

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

“…A root‐mean square retrieval error was then determined from the individually determined retrieval errors. See, for example, Urban [2003] and Verdes et al [2002] for a more detailed discussion of this method and Urban et al [2004a] for a definition of the contribution functions in MOLIERE‐5.…”

Expected performance of the Superconducting Submillimeter‐Wave Limb Emission Sounder compared with aircraft data

“…Retrieved was the volume mixing ratio (VMR) in relative units, that is, x = VMR true /VMR reference , and the temperature in absolute units (Kelvin), as described in detail by Verdes et al [2002]. The reference VMR profiles are the ones shown in Figure 2.…”

Performance Assessment of Balloon-Borne Trace Gas Sounding with the Terahertz Channel of TELIS

“…The relevant pointing information was provided by the Attitude and Heading Reference System (AHRS) [16] and its uncertainty is within 1 arcmin. It has been suggested that the pointing information can be derived from measurements of oxygen emission lines [54][55][56][57][58]. However, due to the very high noise temperature in the TELIS O 2 microwindow, an accurate retrieval of the pointing information is not feasible; further, it is not required because of the high quality of the AHRS data.…”

“…Consequently, the TELIS consortium did not define any dedicated ozone microwindow during these three campaigns. To choose a proper ozone line for the retrieval, one should take into account the energy of the lower state where the transition occurs since this quantity reflects the expected sensitivity to atmospheric temperature [57].…”