A. von Engeln

Pointing and temperature retrieval from millimeter-submillimeter limb soundings

[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. INDEX TERMS: 1640 Global Change: Remote sensing; 3260 Mathematical Geophysics: Inverse theory; 0350 Atmospheric Composition and Structure: Pressure, density, and temperature; 0394 Atmospheric Composition and Structure: Instruments and techniques;

Retrieval of upper stratospheric and mesospheric temperature profiles from Millimeter-Wave Atmospheric Sounder data

The Millimeter-Wave Atmospheric Sounder (MAS) is a shuttle-based instrument, observing the atmosphere in limb sounding geometry. Temperature information is derived from three oxygen lines near 60GHz. Temperature profiles in the altitude range from 30 to 90 km can be measured. The data evaluation is done with the aid of an atmospheric radiative transfer model. Usually, the radiation is assumed to be unpolarized, so that spectral power is a scalar quantity. This assumption is not valid for oxygen lines that show Zeeman splitting in the Earths magnetic field. A more general form of the radiative transfer in which spectral power is represented by a vector has to be used in this case. The obtained information depends on the magnetic field. Using the MAS instrument characteristics, we investigate the possible temperature information that can be obtained from observation of polarized O2 emission lines with a spaceborne instrument. Synthetic retrievals show that the obtained accuracy of the retrieved temperature profile is below 3 K from 30 to 55 km and below 6 K for altitudes up to 90 km. The resolution is 4 km for altitudes of 30 to 50 km and 10 km above. The magnetic parameters influence the accuracy of the obtained profile by as much as 2 K. The obtained MAS temperature profiles were validated by a comparison to data from the Upper Atmosphere Research Satellite (UARS). Three UARS instruments were chosen: Microwave Limb Sounder, Improved Stratospheric and Mesospheric Sounder, and the Cryogenic Limb Array Etalon Spectrometer. All comparisons show similar features for the stratospheric and mesospheric temperatures.

Retrieval of stratospheric temperatures from spaceborne microwave limb sounding measurements

Microwave limb sounding is a well-suited technique for the observation of the composition and temperature of the middle atmosphere. The Shuttle-borne millimeter-wave atmospheric sounder (MAS) measures three oxygen lines in the 61–64 GHz region. Since oxygen is uniformly mixed in the lower and middle atmosphere, the amplitude and shape of the emission lines depend only on temperature and pressure. From these oxygen emission lines, vertical temperature profiles are retrieved with a vertical resolution of 5km in the altitude region of 15–45 km (127–1.5 hPa). The estimated total error is 1.5 K at altitudes of 25–35 km (24.5–5.7 hPa) and up to 5 K above and below this region. Simultaneously with the temperature profile, certain instrument parameters are retrieved. We present the first MAS temperature retrieval results taken at three different locations from measurements of March 31, 1992, during the ATLAS 1 mission. The temperature retrieval results are basically in good agreement with National Center for Environmental Prediction (NCEP) analysis data, but the MAS retrievals have a tendency to low temperatures in the lower stratosphere.

CHAMP Radio Occultation Detection of the Planetary Boundary Layer Top

A simple approach to derive the Planetary Boundary Layer (PBL) top altitude from the CHAllenging Minisatellite Payload (CHAMP) radio occultation data is presented. The lowest sampled altitude is assumed to be determined by the top of the PBL. We average CHAMP measurements for the years 2002 and 2003 over 5 degree latitude longitude boxes and compare them to European Centre for Medium-Range Weather Forecasts (ECMWF) data. The ECMWF PBL top was calculated from the relative humidity gradient with respect to altitude. The altitude where this gradient has its minimum and temperatures are above 273 K is assumed to represent the PBL top. Agreement between the two datasets is good in terms of mean PBL height, especially over sea. The CHAMP data show the major features of PBL height with a realistic transition from stratocumulus regions to shallow and deep cumulus areas. CHAMP also shows a substantial amount of PBL height variability that might proof useful to study PBL dynamics.

Superconducting sub-millimeter wave limb emission sounder SMILES

The main aims of the SMILES project are the development and use of superconducting mixers (superconductor-insulator-superconductor SIS technology) in a heterodyne sub-millimeter receiver for remote sensing of the atmosphere from space. The two frequency bands to be observed, 624.2-628.6 GHz and 649.3-653.1 GHz, are chosen such that the chemistry of the upper troposphere and the stratosphere, together with some climatological aspects, can be investigated. These frequency ranges allow the observation of a number of interesting species, such as ClO, BrO, HO/sub 2/, NO, SO/sub 2/, O/sub 3/, HCl, HOCl, HN0/sub 3/, N/sub 2/0, H/sub 2/0/sub 2/ and 0/sup 18/0. A simulated spectrum is shown.