Expected improvements in the atmospheric humidity profile retrieval using the Megha‐Tropiques microwave payload

Brogniez, Hélène; Kirstetter, Pierre‐Emmanuel; Eymard, Laurence

doi:10.1002/qj.1869

Cited by 33 publications

(39 citation statements)

References 57 publications

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“…Limits of such statistical schemes arise mainly from the training phase performed over a sample of tropical profiles, and from the signature of non-scattering clouds in the scene, as these cannot be accounted for in the radiative transfer computations that are a pre-requisite to the design of the retrieval technique. However, some studies have already shown that the three additional channels of SAPHIR compared to the configuration of the operational 183 GHz radiometers such as AMSU-B or MHS improve the estimation of the relative humidity of the upper part of the troposphere and in its lowest layers (Brogniez et al 2013). …”

Section: Saphir and Megha-tropiquesmentioning

confidence: 99%

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

et al. 2017

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In situ, airborne and satellite measurements are used to characterize the structure of water vapor in the lower tropical troposphere-below the height, z Ã ; of the triple-point isotherm, T Ã : The measurements are evaluated in light of understanding of how lowertropospheric water vapor influences clouds, convection and circulation, through both radiative and thermodynamic effects. Lower-tropospheric water vapor, which concentrates in the first few kilometers above the boundary layer, controls the radiative cooling profile of the boundary layer and lower troposphere. Elevated moist layers originating from a preferred level of convective detrainment induce a profile of radiative cooling that drives circulations which reinforce such features. A theory for this preferred level of cumulus termination is advanced, whereby the difference between T Ã and the temperature at which primary ice forms gives a 'first-mover advantage' to glaciating cumulus convection, thereby concentrating the regions of the deepest convection and leading to more clouds and moisture near the triple point. A preferred level of convective detrainment near T Ã implies relative humidity reversals below zÃ which are difficult to identify using retrievals from satellite-borne microwave and infrared sounders. Isotopologues retrievals provide a hint of such features and their ability to constrain the structure of the vertical humidity profile merits further study. Nonetheless, it will likely remain challenging to resolve dynamically -017-9420-8 important aspects of the vertical structure of water vapor from space using only passive sensors.

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Section: Saphir and Megha-tropiquesmentioning

confidence: 99%

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

et al. 2017

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“…SAPHIR is a cross-track sounder observing the Earth's atmosphere with 6 channels in the 183.31 GHz water vapor strong absorption line. MADRAS is a scanning imager with 9 channels ranging from 18.7 GHz to 157 GHz [2].…”

Section: Satellite Observationsmentioning

confidence: 99%

Retrieval of relative humidity profiles and its associated error from Megha-Tropiques measurements

Sivira

Brogniez

Mallet

et al. 2013

AIP Conference Proceedings

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Abstract. The combination of the two microwave radiometers, SAPHIR and MADRAS, on board the Megha-Tropiques platform is explored to define a retrieval method that estimates not only the relative humidity profile but also the associated confidence intervals. A comparison of three retrieval models was performed, in equal conditions of input and output data sets, through their statistical values (error variance, correlation coefficient and error mean) obtaining a profile of seven layers of relative humidity. The three models show the same behavior with respect to layers, mid-tropospheric layers reaching the best statistical values suggesting a model-independent problem. Finally, the study of the probability density function of the relative humidity at a given atmospheric pressure further gives insight of the confidence intervals.

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“…The SAPHIR sounder and the MADRAS imager are both dedicated to improving the documentation of the atmospheric water cycle. In a previous paper, Brogniez et al (2013) showed the expected improvements for the estimation of the RH profiles thanks to the combination of those two instruments, highlighting the gain of information for both ends of the troposphere when only a subset of the channels of MADRAS are combined to SAPHIR measurements. Despite the short lifetime of MADRAS, the availability of a few months of measurements constitutes a test bed for future missions, such as the Second Generation of the Meteorological Operational satellite program (MetOp-SG, EUMETSAT Polar Satellite) planned for launch in 2020.…”

Section: R G Sivira Et Al: Relative Humidity Profiling With Megha-mentioning

confidence: 99%

“…Indeed, as underlined by Brogniez et al (2013), the representation of the cloudy conditions in a training database still presents a limit because reference profiles of cloudy situations with known uncertainties are difficult to gather, which could introduce unwanted additional errors in the methodology. Moreover, we chose to restrict the main part of the current work to a full description of the retrieval models dedicated to oceanic situations.…”

Section: The Radiosonde Profilesmentioning

confidence: 99%

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A layer-averaged relative humidity profile retrieval for microwave observations: design and results for the Megha-Tropiques payload

et al. 2015

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Abstract.A statistical method trained and optimized to retrieve seven-layer relative humidity (RH) profiles is presented and evaluated with measurements from radiosondes. The method makes use of the microwave payload of the Megha-Tropiques platform, namely the SAPHIR sounder and the MADRAS imager. The approach, based on a generalized additive model (GAM), embeds both the physical and statistical characteristics of the inverse problem in the training phase, and no explicit thermodynamical constraint -such as a temperature profile or an integrated water vapor content -is provided to the model at the stage of retrieval. The model is built for cloud-free conditions in order to avoid the cases of scattering of the microwave radiation in the 18.7-183.31 GHz range covered by the payload. Two instrumental configurations are tested: a SAPHIR-MADRAS scheme and a SAPHIR-only scheme to deal with the stop of data acquisition of MADRAS in January 2013 for technical reasons. A comparison to learning machine algorithms (artificial neural network and support-vector machine) shows equivalent performance over a large realistic set, promising low errors (biases < 2.2 %RH) and scatters (correlations > 0.8) throughout the troposphere (150-900 hPa). A comparison to radiosonde measurements performed during the international field experiment CINDY/DYNAMO/AMIE (winter 2011-2012) confirms these results for the mid-tropospheric layers (correlations between 0.6 and 0.92), with an expected degradation of the quality of the estimates at the surface and top layers. Finally a rapid insight of the estimated large-scale RH field from Megha-Tropiques is presented and compared to ERA-Interim.

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Expected improvements in the atmospheric humidity profile retrieval using the Megha‐Tropiques microwave payload

Cited by 33 publications

References 57 publications

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

Structure and Dynamical Influence of Water Vapor in the Lower Tropical Troposphere

Retrieval of relative humidity profiles and its associated error from Megha-Tropiques measurements

A layer-averaged relative humidity profile retrieval for microwave observations: design and results for the Megha-Tropiques payload

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