Validation of revised methane and nitrous oxide profiles from MIPAS-ENVISAT
Johannes PlieningerAlexandra LaengStefan LoßowT. von ClarmannG. P. StillerS. KellmannA. LindenMichael KieferK. A. WalkerStefan NoëlMark E. HervigM. J. McHughA. LambertJ. UrbanJ. W. ElkinsD. Murtagh
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Abstract. Improved versions of CH4 and N2O profiles derived at the Institute of Meteorology and Climate Research and Instituto de Astrofísica de Andalucía (CSIC) from spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have become available. For the MIPAS full resolution period (2002–2004) these are V5H_CH4_21 and V5H_N2O_21 and for the reduced resolution period (2005–2012) these are V5R_CH4_224, V5R_CH4_225, V5R_N2O_224 and V5R_N2O_225. Here, we compare CH4 profiles to those measured by the Fourier Transform Spectrometer on board of the Atmospheric Chemistry Experiment (ACE-FTS), the HALogen Occultation Experiment (HALOE) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) and to the Global Cooperative Air Sampling Network (GCASN) surface data. We find the MIPAS CH4 profiles below 25 km to be typically higher in the order of 0.1 ppmv for both measurement periods. N2O profiles are compared to those measured by ACE-FTS, the Microwave Limb Sounder on board of the Aura satellite (Aura-MLS) and the Sub-millimetre Radiometer on board of the Odin satellite (Odin-SMR) as well as to the Halocarbons and other Atmospheric Trace Species Group (HATS) surface data. The mixing ratios from the satellite instruments agree well for the full resolution period. For the reduced resolution period, MIPAS produces similar values as Odin-SMR, but higher values than ACE-FTS and HATS. Below 27 km, the MIPAS profiles show higher mixing ratios than Aura-MLS, and lower values between 27 and 41 km. Cross comparisons between the two MIPAS measurement periods show that they generally agree quite well, but, especially for CH4, the reduced resolution period seems to produce slightly higher mixing ratios than the full resolution data.Keywords:
SCIAMACHY
Atmospheric sounding
Trace gas
Spectral resolution
Occultation
Abstract. Improved versions of CH4 and N2O profiles derived at the Institute of Meteorology and Climate Research and Instituto de Astrofísica de Andalucía (CSIC) from spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have become available. For the MIPAS full resolution period (2002–2004) these are V5H_CH4_21 and V5H_N2O_21 and for the reduced resolution period (2005–2012) these are V5R_CH4_224, V5R_CH4_225, V5R_N2O_224 and V5R_N2O_225. Here, we compare CH4 profiles to those measured by the Fourier Transform Spectrometer on board of the Atmospheric Chemistry Experiment (ACE-FTS), the HALogen Occultation Experiment (HALOE) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) and to the Global Cooperative Air Sampling Network (GCASN) surface data. We find the MIPAS CH4 profiles below 25 km to be typically higher in the order of 0.1 ppmv for both measurement periods. N2O profiles are compared to those measured by ACE-FTS, the Microwave Limb Sounder on board of the Aura satellite (Aura-MLS) and the Sub-millimetre Radiometer on board of the Odin satellite (Odin-SMR) as well as to the Halocarbons and other Atmospheric Trace Species Group (HATS) surface data. The mixing ratios from the satellite instruments agree well for the full resolution period. For the reduced resolution period, MIPAS produces similar values as Odin-SMR, but higher values than ACE-FTS and HATS. Below 27 km, the MIPAS profiles show higher mixing ratios than Aura-MLS, and lower values between 27 and 41 km. Cross comparisons between the two MIPAS measurement periods show that they generally agree quite well, but, especially for CH4, the reduced resolution period seems to produce slightly higher mixing ratios than the full resolution data.
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The Global Ozone Monitoring Experiment (GOME) and the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), are two European experiments which will fly on satellite platforms in the 1990s. GOME is a small scale version of SCIAMACHY and together they form the SCIAMACHY scientific project. The principal scientific objective is the global determination of the distributions of atmospheric constituents: trace gases, aerosol, and cloud. Special emphasis is placed in this project on stratospheric and tropospheric measurements. GOME observes between 240 and 790 nm in nadir sounding, whereas SCIAMACHY will sound the atmosphere in nadir, limb and solar, and lunar occultation viewing geometries between 240 and 2380 nm.
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Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is an infrared (IR) limb emission spectrometer on the Envisat platform. It measures trace gas distributions during day and night, pole-to-pole, over an altitude range from 6 to 70 km in nominal mode and up to 170 km in special modes, depending on the measurement mode, producing more than 1000 profiles day−1. We present the results of a validation study of methane, version V5R_CH4_222, retrieved with the IMK/IAA (Institut für Meteorologie und Klimaforschung, Karlsruhe/Instituto de Astrofisica de Andalucia, Grenada) MIPAS scientific level 2 processor. The level 1 spectra are provided by the ESA (European Space Agency) and version 5 was used. The time period covered is 2005–2012, which corresponds to the period when MIPAS measured trace gas distributions at a reduced spectral resolution of 0.0625 cm−1. The comparison with satellite instruments includes the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), the HALogen Occultation Experiment (HALOE), the Solar Occultation For Ice Experiment (SOFIE) and the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY). Furthermore, comparisons with MkIV balloon-borne solar occultation measurements and with air sampling measurements performed by the University of Frankfurt are presented. The validation activities include bias determination, assessment of stability, precision validation, analysis of histograms and comparison of corresponding climatologies. Above 50 km altitude, MIPAS methane mixing ratios agree within 3 % with ACE-FTS and SOFIE. Between 30 and 40 km an agreement within 3 % with SCIAMACHY has been found. In the middle stratosphere, there is no clear indication of a MIPAS bias since comparisons with various instruments contradict each other. In the lower stratosphere (below 25 km) MIPAS CH4 is biased high with respect to satellite instruments, and the most likely estimate of this bias is 14 %. However, in the comparison with CH4 data obtained from cryogenic whole-air sampler (cryosampler) measurements, there is no evidence of a high bias in MIPAS between 20 and 25 km altitude. Precision validation is performed on collocated MIPAS–MIPAS pairs and suggests a slight underestimation of its uncertainties by a factor of 1.2. No significant evidence of an instrumental drift has been found.
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Abstract. Improved versions of CH4 and N2O profiles derived at the Institute of Meteorology and Climate Research and Instituto de Astrofísica de Andalucía (CSIC) from spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) have become available. For the MIPAS full-resolution period (2002–2004) these are V5H_CH4_21 and V5H_N2O_21 and for the reduced-resolution period (2005–2012) these are V5R_CH4_224, V5R_CH4_225, V5R_N2O_224 and V5R_N2O_225. Here, we compare CH4 profiles to those measured by the Fourier Transform Spectrometer on board of the Atmospheric Chemistry Experiment (ACE-FTS), the HALogen Occultation Experiment (HALOE) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY), to the Global Cooperative Air Sampling Network (GCASN) surface data. We find the MIPAS CH4 profiles below 25 km to be typically higher of the order of 0.1 ppmv for both measurement periods. N2O profiles are compared to those measured by ACE-FTS, the Microwave Limb Sounder on board of the Aura satellite (Aura-MLS) and the Sub-millimetre Radiometer on board of the Odin satellite (Odin-SMR) as well as to the Halocarbons and other Atmospheric Trace Species Group (HATS) surface data. The mixing ratios of the satellite instruments agree well with each other for the full-resolution period. For the reduced-resolution period, MIPAS produces similar values as Odin-SMR, but higher values than ACE-FTS and HATS. Below 27 km, the MIPAS profiles show higher mixing ratios than Aura-MLS, and lower values between 27 and 41 km. Cross-comparisons between the two MIPAS measurement periods show that they generally agree quite well, but, especially for CH4, the reduced-resolution period seems to produce slightly higher mixing ratios than the full-resolution data.
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The spectrometer SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) on-board ENVISAT is measuring solar irradiances and Earthshine radiances from the UV to the NIR spectral region in nadir, limb and lunar/solar occultation geometry. From these measurements the amount and distribution of various atmospheric constituents are derived (O3, BrO, OClO, SO2, H2CO, NO2, CO, CO2, CH4, H2O, clouds, and aerosols).
To assure the quality of these data products at any time during the whole mission a detailed knowledge of the instrument status and behaviour is mandatory. To achieve this a comprehensive monitoring concept has been developed and implemented, involving various dedicated calibration and monitoring measurements.
We present selected results from the analysis of these monitoring data. Special emphasis is placed on the performance monitoring for the various light paths and the derivation of degradation correction factors for operational data products.
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A new, fast radiative transfer model has been developed for retrievals from the future limb measurements of SCIAMACHY. It has been used to characterise UV-vis-NIR limb measurements. The hyperspectral spectrometer SCIAMACHY will be launched aboard the European satellite Envisat in October 2001. It will measure atmospheric radiance spectra extending from the UV to the NIR spectral region, i.e., 240–2380 nm, with a moderate resolution of 0.24–1.5 nm. SCIAMACHY will operate in three measurement geometries: nadir, limb and occultation. SCIAMACHY’s hyperspectral capabilities will enable the simultaneous retrieval of a large set of atmospheric parameters from each individual measurement. Among the retrieval targets are the trace gases O3, NO2, OClO, BrO, SO2, HCHO, H2O, CH4, CO2, CO, and N2O. Additionally, temperature, aerosol and cloud parameters will be determined. SCIAMACHY’s measurements in limb geometry will provide vertically resolved profiles of the retrieval parameters. Since the limb measurements are conceptually new, no retrieval algorithms and radiative transfer models have been established for them yet. In this thesis, a new, fast radiative transfer model for UV-vis-NIR limb radiances has been developed, implemented, and validated. It takes into account the sphericity of the atmosphere and up to two orders of scattering and surface reflection. Since the radiance and weighting functions for all atmospheric parameters are calculated from analytical formulae, the model is fast. Due to the combination of these properties, the model is a unique tool for retrievals from UV-vis-NIR limb measurements. An instrument model with field-of-view integration and signal-to-noise computation has been developed. It models SCIAMACHY’s real characteristics as measured in the laboratory. Retrieval algorithms based on the optimal estimation technique have also been implemented. They have been combined with the new radiative transfer and instrument models in the new program package SCIARAYS. The program package SCIARAYS has been applied for the characterisation of UV-vis-NIR limb measurements in several ways: The radiances and weighting functions calculated with SCIARAYS have been compared to those calculated with the radiative transfer model CDIPI, which accounts for full multiple scattering, but is much much slower. The second order of scattering and reflection modelled by SCIARAYS yields 60–95 % of the full multiply scattered radiance, depending on wavelength and solar coordinates. The simulated weighting functions agree within 10 %. Their feature at the tangent height is particularly well reproduced. Therefore, SCIARAYS’ weighting functions
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