Cirrus cloud shape detection by tomographic extinction retrievals from infrared limb emission sounder measurements

Ungermann, Jörn; García, Irene Bartolomé; Grießbach, Sabine; Spang, Reinhold; Rolf, Christian; Krämer, Martina; Höpfner, Michael; Riese, Martin

doi:10.5194/amt-13-7025-2020

Cited by 5 publications

(5 citation statements)

References 55 publications

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“…This is exemplified by the extinction profiles shown in Fig. 22, which were retrieved with different aperture sizes based on the retrieval approach discussed by Ungermann et al (2020). For a PSF with an assumed aperture smaller than 3.6 cm, the extinction even drops below the background values found at higher altitude values above the cloud top.…”

Section: Point Spread Functionmentioning

confidence: 85%

Quantification and mitigation of the instrument effects and uncertainties of the airborne limb imaging FTIR GLORIA

et al. 2022

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Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an infrared imaging FTS (Fourier transform spectrometer) with a 2-D infrared detector that is operated on two high-flying research aircraft. It has flown on eight campaigns and measured along more than 300 000 km of flight track. This paper details our instrument calibration and characterization efforts, which, in particular, almost exclusively leverage in-flight data. First, we present the framework of our new calibration scheme, which uses information from all three available calibration sources (two blackbodies and upward-pointing “deep space” measurements). Part of this scheme is a new algorithm for correcting the erratically changing nonlinearity of a subset of detector pixels and the identification of the remaining bad pixels. Using this new calibration, we derive a 1σ bound of 1 % on the instrument gain error and a bound of 30 nW cm−2 sr−1 cm on the instrument offset error. We show how we can examine the noise and spectral accuracy for all measured atmospheric spectra and derive a spectral accuracy of 5 ppm on average. All these errors are compliant with the initial instrument requirements. We also discuss, for the first time, the pointing system of the GLORIA instrument. Combining laboratory calibration efforts with the measurement of astronomical bodies during the flight, we can achieve a pointing accuracy of 0.032∘, which corresponds to one detector pixel. The paper concludes with a brief study of how these newly characterized instrument parameters affect temperature and ozone retrievals. We find that the pointing uncertainty and, to a lesser extent, the instrument gain uncertainty are the main contributors to the error in the result.

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Section: Point Spread Functionmentioning

confidence: 85%

Quantification and mitigation of the instrument effects and uncertainties of the airborne limb imaging FTIR GLORIA

et al. 2022

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“…This is exemplified in the extinction profile in Fig. 22 retrieved with different aperture sizes based on the retrieval approach discussed by Ungermann et al (2020). For a PSF with an assumed aperture smaller than 3.6 cm, extinction drops even below the background values found at higher altitude values above the cloud top.…”

Section: Point Spread Functionmentioning

confidence: 86%

Quantification and mitigation of the airborne limb imaging FTIR GLORIA instrument effects and uncertainties

Ungermann

Kleinert

Maucher

et al. 2021

Preprint

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Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an infrared imaging FTS spectrometer with a 2-D infrared detector operated on two high flying research aircrafts. It has flown on eight campaigns and measured along more than 300 000 km of flight track. This paper details our instrument calibration and characterization efforts, which in particular leverage almost exclusively in-flight data. First, we present the framework of our new calibration scheme, which uses information from all three available calibration measurements (two blackbodies and upward pointing deep space measurements). Part of this scheme is a new correction algorithm correcting the erratically changing non-linearity of a subset of detector pixels and the identification of remaining bad pixels. Using this new calibration, we derive a 1-σ bound of 1 % on the instrumental gain error and a bound of 30 nW cm−2 sr−1 cm on the instrumental offset error. We show how we can examine the noise and spectral accuracy for all measured atmospheric spectra and derive a spectral accuracy of 5 ppm, on average. All these errors are compliant with the initial instrument requirements. We also discuss, for the first time, the pointing system of the GLORIA instrument. Combining laboratory calibration efforts with the measurement of astronomical bodies during the flight, we can derive a pointing accuracy of 0.032°, which corresponds to one detector pixel. The paper concludes with a brief study on how these newly characterised instrumental parameters affect temperature and ozone retrievals. We find that, first, the pointing uncertainty and, second, the instrumental gain uncertainty introduce the largest error in the result.

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“…Although, these are typical caveats for cloud and trace gas retrievals of limb sounders, modified instruments like limb imager allow substantial improvements of macroscopic cloud parameter with refined observation and retrieval techniques (e.g. 2D/3D and tomographic retrieval techniques, Ungermann et al, 2020). However, the CRISTA measurement capabilities are still unique for the limb IR technique.…”

Section: Crista Instrumentmentioning

confidence: 99%

Radiative impact of thin cirrus clouds in the lowermost stratosphere and tropopause region

Spang

Müller

Rap

2023

Preprint

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Abstract. Cirrus clouds play an important role in the radiation budget of the Earth. Despite recent progress in remote sensing observations of cirrus in general, the radiative impact of thin cirrus clouds in the tropopause region and in the lowermost stratosphere remains poorly constrained. This is due to their small vertical extent and optical depth, which make them very difficult to observe for most instruments. In addition, their shortwave (cooling) and longwave (warming) radiative effects (RE) are often in approximate balance, which together with uncertainties regarding the shape and size of cirrus particles, make their overall impact on climate difficult to quantify. In this study the SOCRATES (Suite Of Community RAdiative Transfer codes based on Edwards and Slingo) radiative transfer model was used to calculate the shortwave and longwave RE for observed thin cirrus during the second space shuttle mission by the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA-2) instrument. Unusual high cloud top heights with respect to the tropopause and rather high occurrence rates have been retrieved in earlier studies. However, the question remained open if these optically ultra thin cirrus clouds (UTC), so far not considered in global model calculation, are of importance for the Earth's radiation budget. Using sensitivity simulations with different ice effective particle size and shape, we provide an uncertainty range for the RE of UTCs in the lowermost stratosphere and tropopause region during both summer and winter months. Cloud top height and ice water content are based on CRISTA-2 retrievals, while the cloud vertical thicknesses were assumed to be 0.5 or 2 km. Our results indicate that if the ice crystals of these thin cirrus clouds are assumed to be spherical, then their net RE is generally positive (warming). In contrast, if they are assumed to be aggregates, a less likely habit for this high altitude cirrus type, then their net RE is generally negative (cooling) during summer months and positive (warming) during winter months. The cooling or warming RE is in the order of ±(0.1–0.01) W/m2 for a realistic global cloud coverage of 10 %, similar to the magnitude of the contrail cirrus radiative forcing best estimate of ~0.1 W/m2. RE is also dependent on the cloud vertical extent and consequently the optically thickness and effective radius (Reff) of the particle size distribution (e.g. Reff increase from 10 to 30 µm results in a factor ≃ 3 smaller short and longwave effects). We argue that the radiative impact of UTC clouds in the lowermost stratosphere and tropopause region needs to be better addressed in observations and need to be taken into account in climate simulations.

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Cirrus cloud shape detection by tomographic extinction retrievals from infrared limb emission sounder measurements

Cited by 5 publications

References 55 publications

Quantification and mitigation of the instrument effects and uncertainties of the airborne limb imaging FTIR GLORIA

Quantification and mitigation of the instrument effects and uncertainties of the airborne limb imaging FTIR GLORIA

Quantification and mitigation of the airborne limb imaging FTIR GLORIA instrument effects and uncertainties

Radiative impact of thin cirrus clouds in the lowermost stratosphere and tropopause region

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