Anne Kleinert

Design and characterization of the balloon-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B2)

MIPAS-B2 is a balloon-borne limb-emission sounder for atmospheric research. The heart of the instrument is a Fourier spectrometer that covers the mid-infrared spectral range (4-14 microns) and operates at cryogenic temperatures. Essential for this application is the sophisticated line-of-sight stabilization system, which is based on an inertial navigation system and is supplemented with an additional star reference system. The major scientific benefit of the instrument is the simultaneous detection of complete trace gas families in the stratosphere without restrictions concerning the time of day and viewing directions. The specifications, the design considerations, the actual realization of the instrument, and the results of characterization measurements that have been performed are described.

NOy partitioning and budget and its correlation with N2O in the Arctic vortex and in summer midlatitudes in 1997

Vertical profiles of the most important species of nocturnal total reactive nitrogen (NO y = NO 2 + HNO 3 + CIONO 2 + 2 N 2 O 5 + HO 2 NO 2 ) together with its source gas N 2 O were retrieved from infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloon-borne version (MIPAS-B) instrument inside the late winter arctic vortex from Kiruna (Sweden, 68°N) on 24 March 1997 and in summer midlatitudes from Gap (France, 44°N) on 2 July 1997. The measured data were compared to calculations performed with the three-dimensional chemistry transport model (CTM) Karlsruhe Simulation model of the Middle Atmosphere (KASIMA). The results show that in the late winter arctic vortex most of the available nitrogen and chlorine is in the form of HNO 3 and CIONO 2 , respectively. An anomalous N 2 O-NO y correlation observed in March 1997 appears to be caused to a large extent by quasi-horizontal mixing of air masses across the vortex edge. However, near 20 km some denitrification of ∼1.5 to 2 ppbv NO y could be observed. The N 2 O profile measured in July 1997 indicates remnants of polar vortex air and is not reproduced by the CTM at the same location. However, the profile shapes of the individual compounds of the NO y family as well as the NO x /NO y ratio are reproduced fairly well by the model.

Correction of detector nonlinearity for the balloonborne Michelson Interferometer for Passive Atmospheric Sounding

The detectors used in the cryogenic limb-emission sounder MIPAS-B2 (Michelson Interferometer for Passive Atmospheric Sounding) show a nonlinear response, which leads to radiometric errors in the calibrated spectra if the nonlinearity is not taken into account. In the case of emission measurements, the dominant error that arises from the nonlinearity is the changing detector responsivity as the incident photon load changes. The effect of the distortion of a single interferogram can be neglected. A method to characterize the variable responsivity and to correct for this effect is proposed. Furthermore, a detailed error estimation is presented.

Phase determination for a Fourier transform infrared spectrometer in emission mode.

Beam-splitter emission strongly influences the spectra measured with a Fourier transform spectrometer (FTS) as it affects the entire phase behavior, in particular in emission spectroscopy. The various radiation contributions of the scene and the FTS itself have different phases in the complex spectrum. As a specific feature, the radiation of the beam splitter is rotated by approximately pi/2 relative to the scene effective radiation. By classical methods of phase correction, the radiation components of different phases are mixed in the complex plane, which may lead to serious errors in the calibrated spectra. For this reason, the nature of the FTS phase has been studied, and a statistical phase determination method has been developed. It allows us to determine the phase function of the scene by minimizing the correlation between the imaginary and the real parts of the complex spectrum and by reducing the variance of the imaginary part. Thus phase accuracies of 10 to 30 mrad can be achieved. In addition, the remaining error of the phase can be calculated for each individual spectrum. The total phase error and its effect on the spectra are discussed.

The global picture of the atmospheric composition provided by MIPAS on Envisat

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a mid-infrared emission spectrometer which is part of the core payload of the Envisat satellite, launched by ESA in March 2002. It provides unique observations of the atmospheric spectral radiances in the 4.15 - 14.6 μm spectral interval with innovative limb scanning capabilities for the three dimensional observation of the atmospheric composition and processes. The species, the processes and events that have been studied with this instrument in its 10 years of operation are briefly reviewed.

In-flight blackbody calibration sources for the GLORIA interferometer

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) deployed on board different research aircraft shall provide a detailed picture of the UTLS region. GLORIA uses a two-dimensional detector array for infrared limb-observations. The GLORIA in-flight calibration system consists of two identical large-area high-precision blackbodies, which are independently controlled at two different temperatures. Thermo-Electric Coolers are used to control the temperature of the blackbodies. The system has been comprehensively characterized for its spatially and spectrally resolved radiation properties in terms of radiation temperature traceable to the international temperature scale (ITS-90) at the national metrology institute of Germany (PTB).

Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

Limb sounding instruments play an important role in the monitoring of climate trends, as they provide a good vertical resolution. Traceability to the International System of Units (SI) via onboard reference or transfer standards is needed to compare trend estimates from multiple instruments. This study investigates the required uncertainty of these radiation standards to properly resolve decadal trends of climate-relevant trace species like ozone, water vapor, and temperature distribution for the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). Temperature nonuniformities of the onboard reference blackbodies, used for radiometric calibration, have an impact on the calibration uncertainty. The propagation of these nonuniformities through the retrieval is analyzed. A threshold for the maximum tolerable uncertainty of the blackbody temperature is derived, so that climate trends can be significantly identified with GLORIA.

Airborne limb-imaging measurements of temperature, HNO 3 , O 3 , ClONO 2 , H 2 O and CFC-12 during the Arctic winter 2015/16: characterization, in-situ validation and comparison to Aura/MLS

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) was operated on board the German High Altitude and Long Range Research Aircraft (HALO) during the PGS (POLSTRACC/GWLCYCLE/SALSA) aircraft campaigns in the Arctic winter 2015/2016. Research flights were conducted from 17 December 2015 until 18 March 2016 within 25–87 N, 80W–30 E. From the GLORIA infrared limb-emission measurements, two-dimensional cross sections of temperature, HNO3, O3, ClONO2, H2O and CFC-12 are retrieved. During 15 scientific flights of the PGS campaigns the GLORIA instrument measured more than 15 000 atmospheric profiles at high spectral resolution. Dependent on flight altitude and tropospheric cloud cover, the profiles retrieved from the measurements typically range between 5 and 14 km, and vertical resolutions between 400 and 1000 m are achieved. The estimated total (random and systematic) 1σ errors are in the range of 1 to 2 K for temperature and 10 % to 20 % relative error for the discussed trace gases. Comparisons to in situ instruments deployed on board HALO have been performed. Over all flights of this campaign the median differences and median absolute deviations between in situ and GLORIA observations are−0.75K±0.88 K for temperature, −0.03ppbv± 0.85 ppbv for HNO3, −3.5ppbv± 116.8 ppbv for O3,−15.4pptv±102.8 pptv for ClONO2,−0.13ppmv± 0.63 ppmv for H2O and −19.8pptv± 46.9 pptv for CFC-12. Seventy-three percent of these differences are within twice the combined estimated errors of the cross-compared instruments. Events with larger deviations are explained by atmospheric variability and different sampling characteristics of the instruments. Additionally, comparisons of GLORIA HNO3 and O3 with measurements of the Aura Microwave Limb Sounder (MLS) instrument show highly consistent structures in trace gas distributions and illustrate the potential of the high-spectral-resolution limb-imaging GLORIA observations for resolving narrow mesoscale structures in the upper troposphere and lower stratosphere (UTLS).

Characterization of Large Area Calibration Blackbodies for the Imaging FTS GLORIA

GLORIA is an imaging infrared FTS measuring atmospheric limb emission spectra from aircraft. For radiometric calibration it uses two on-board blackbodies. Accuracy and homogeneity of these blackbodies are characterized and traced to ITS-90.

An in-flight blackbody calibration source for the GLORIA interferometer onboard an airborne research platform

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) deployed on board different research aircraft provides detailed pictures of the Upper Troposphere/Lower Stratosphere (UTLS) region. GLORIA uses a two-dimensional detector array for infrared limb observations. GLORIAs in-flight calibration sources are two identical large-area high-precision blackbodies, which are independently controlled at two different temperatures. Thermo-Electric Coolers (TECs) are used to control the temperature of the calibration sources. The calibration sources have been comprehensively characterized for their spatially and spectrally resolved radiation properties in terms of radiation temperature traceable to the International Temperature Scale (ITS-90) at the Physikalisch-Technische Bundesanstalt (PTB), the national metrology institute of Germany.