Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations

Chen, Xiuhong; Huang, Xianglei

doi:10.5194/amt-9-6013-2016

Cited by 2 publications

(1 citation statement)

References 31 publications

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“…This is especially the case in most trace gas (e.g. Warner et al, 2013;Van Damme et al, 2017) and dust retrieval schemes (DeSouza-Machado et al, 2010;Capelle et al, 2018;Clarisse et al, 2019) or for deriving the Earth outgoing longwave radiation (OLR) budget (Loeb et al, 2003;Chen and Huang, 2016;Whitburn et al, 2020), as the presence of even small cloud amounts in the instrument field of view will significantly impact the radiance at the top of the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

et al. 2022

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Abstract. With more than 15 years of continuous and consistent measurements, the Infrared Atmospheric Sounding Interferometer (IASI) radiance dataset is becoming a reference climate data record. To be exploited to its full potential, it requires a cloud filter that is accurate, unbiased over the full IASI life span and strict enough to be used in satellite data retrieval schemes. Here, we present a new cloud detection algorithm which combines (1) a high sensitivity, (2) a good consistency over the whole IASI time series and between the different copies of the instrument flying on board the suite of Metop satellites, and (3) simplicity in its parametrization. The method is based on a supervised neural network (NN) and relies, as input parameters, on the IASI radiance measurements only. The robustness of the cloud mask over time is ensured in particular by avoiding the IASI channels that are influenced by CO2, N2O, CH4, CFC-11 and CFC-12 absorption lines and those corresponding to the ν2 H2O absorption band. As a reference dataset for the training, version 6.5 of the operational IASI Level 2 (L2) cloud product is used. We provide different illustrations of the NN cloud product, including comparisons with other existing products. We find very good agreement overall with version 6.5 of the operational IASI L2 with an identical mean annual cloud amount and a pixel-by-pixel correspondence of about 87 %. The comparison with the other cloud products shows a good correspondence in the main cloud regimes but with sometimes large differences in the mean cloud amount (up to 10 %) due to the specificities of each of the different products. We also show the good capability of the NN product to differentiate clouds from dust plumes.

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Section: Introductionmentioning

confidence: 99%

A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

et al. 2022

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Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements

et al. 2020

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3Space-based measurements of the Outgoing Longwave Radiation (OLR) are essential for the study of the Earth's climate system. While the CERES instrument provides accurate measurements of this quantity, its measurements are not spectrally resolved. Here we present a high-resolution OLR product (sampled at 0.25 cm −1 ), derived from measurements of the IASI satellite sounder. The applied methodology relies on pre-calculated Angular Dependent Models (ADMs). These are usually calculated for ten to hundreds of different scene types (characterized by surface and atmosphere parameters).To guarantee accurate results in the range 645-2300 cm −1 covered by IASI, we constructed ADMs for over 140,000 scenes. These were selected from one year of CAMS reanalysis data. A dissimilarity-based selection algorithm was applied to choose these scenes as different from each other as possible, thereby maximizing the performance on real data, whilst keeping the number of scenes manageable. A comparison of the IASI OLR integrated over the 645-2300 cm −1 range was performed with the longwave broadband OLR products from CERES and the AIRS instrument. The latter are systematically higher due to the contribution of the far infrared to the total IR spectral range, but as expected exhibit generally high spatial correlations with the IASI OLR, except for some areas in the tropical region. We also compared the IASI OLR against the spectrally resolved OLR derived from AIRS. A good agreement was found above 1200 cm −1 while AIRS OLR appeared to be systematically higher in the atmospheric window region, likely related to differences in overpass time or to the use of a different cloud detection algorithm.The top-of-the-atmosphere (TOA) thermal flux, also referred to as the Earth's Outgoing Long- 45 wave Radiation (OLR) [W m −2 ], represents the total radiation emitted by the Earth-atmosphere 46 system into space. As part of the Earth's radiation budget, it reflects how the Earth-atmosphere sys-47 65 by using empirical angular distribution models (ADMs) which allow characterizing the angular 66 dependence of the Earth's radiation field for different scene types (denoted s) with distinct surface 67 and atmospheric anisotropic characteristics. Each of these ADMs consists of a set of anisotropic 68 factors (R s,ν (θ ,φ )) defined as the ratio of the equivalent Lambertian flux to the actual flux (Smith 69 et al. 1986; Suttles et al. 1988) that directly link the directional radiance observations to the OLR 70(for simplicity, the dependencies on x, y and t for L ν (θ , φ ) and F ν are omitted hereafter):The ADMs can be derived directly from the radiance measurements relying on the so-called 72 sorting-into-angular bins method (Suttles et al. 1989) or calculated from synthetic spectra con-73 structed for different angles of view using radiative transfer models (e.g. Huang et al. 2008). 74 The very first OLR measurements were collected by the Explorer VII satellite launched in 75 1959 (Suomi 1960), which operated during a period of 7 months. It was not un...

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Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations

Cited by 2 publications

References 31 publications

A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements

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Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations

Cited by 2 publications

References 31 publications

A CO2-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

A CO2-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements

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A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications

A CO₂-independent cloud mask from Infrared Atmospheric Sounding Interferometer (IASI) radiances for climate applications