Stefan Bühler

Water vapor continuum: absorption measurements at 350 GHz and model calculations

Abstract Absolute absorption rates of pure water vapor and mixtures of water vapor and nitrogen have been measured in the laboratory at 350 GHz . The dependence on pressure and temperature has been obtained. Additionally, a water vapor continuum parameter estimation, taking even the previous laboratory measurements from 150 to 350 GHz into account, is performed.

One-dimensional variational (1-D Var) retrieval of temperature, water vapor, and a reference pressure from radio occultation measurements : A sensitivity analysis

A 1-D Var retrieval study of simulated radio occultation measurements is presented. Temperature and a water vapor profile are retrieved along with a reference pressure to generate the pressure pr ...

Measurement of tropospheric/stratospheric transmission at 10–35 GHz for H2O retrieval in low Earth orbiting satellite links

[1]xa0Active microwave limb sounding is a possible technique for measuring water vapor in the upper troposphere and lower stratosphere, and here a first assessment of the retrieval capabilities of transmission measurements in the range 10–35 GHz is presented. The proposed observing system consists of a constellation of low Earth orbiters measuring atmospheric transmission at the frequencies 10.3, 17.2, and 22.6 GHz. The use of these relatively long wavelengths guarantees a minimal, for being a remote sensing technique, influence from scattering. The original objective of the measurements was to derive water vapor profiles, but the potential to retrieve the liquid water content of clouds was also identified during the study. Retrieval errors due to thermal noise, gain instability, and spectroscopic uncertainties were considered. With the assumed instrument characteristics a measurement precision for water vapor in the upper troposphere of 5–10% is obtained, with capability to observe through ice clouds and clouds with a low water content.

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;

A Hotelling transformation approach for rapid inversion of atmospheric spectra

Atmospheric observations from space often result in spectral data of large dimensions. To allow an optimal inversion of the observed spectra it can be necessary to map the data into a space of smaller dimension. Here several data reduction techniques based on eigenvector expansions of the spectral space are compared. The comparison is done by inverting simulated observations from a microwave limb sounder, the Odin-SMR. For the examples tested, reductions exceeding two orders of magnitude with no negative influence on the retrieval performance are demonstrated. The techniques compared include a novel method developed especially for atmospheric inversions, based on the weighting functions of the variables to be retrieved. The new method shows an excellent performance in practical tests and is both computationally more effective and more flexible than the standard Hotelling transformation.

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.

Temperature profile determination from microwave oxygen emissions in limb sounding geometry

[1]xa0We present a theoretical investigation of the temperature profile retrieval capabilities of oxygen emission lines in the microwave. The main focus is on two strong lines, both allowing temperature retrieval throughout the mesosphere. One is within the oxygen cluster at 61.15 GHz, the other one is isolated at 118.75 GHz. A thorough comparison of these two lines is presented. Several instrumental parameters such as system noise temperature, antenna beam width, filter width, and coverage of the line are assessed, as well as the possible impact of an error in the spectroscopic parameters. The instrumental setup follows roughly the specifications for the Millimeter Wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER) instrument, serving as a basis for a modern passive microwave instrument. The instrumental parameters have also been varied in order to allow comparisons with two instruments that use the 118.75-GHz line for temperature profile determination, the Odin submillimeter radiameter (SMR) and the EOS microwave limb sounder (MLS). Simultaneous retrieval of temperature and pointing bias is performed with the Optimal Estimation Method. We find temperature retrieval errors of <5 K in the mesosphere, and at sub-Kelvin level in the lower stratosphere. Good knowledge of spectroscopic parameters is required for accurate retrievals. The simultaneous retrieval of a pointing bias can reduce the impact of spectroscopic parameter errors on the temperature retrieval.

Temperature profile retrieval from surface to mesopause by combining GNSS radio occultation and passive microwave limb sounder data

Temperature profile retrieval from surface to mesopause by combining GNSS radio occultation and passive microwave limb sounder data

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.