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An improved fast radiative transfer model for special sensor microwave imager/sounder upper atmosphere sounding channels

Authors

  • Yong Han,

    1. Center for Satellite Applications and Research, National Environmental Satellite, Data, and Information Service, NOAA, Camp Springs, Maryland, USA
    2. Joint Center for Satellite Data Assimilation, Camp Springs, Maryland, USA
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  • Paul van Delst,

    1. Science Applications International Corporation, Camp Springs, Maryland, USA
    2. Environmental Modeling Center, National Center for Environmental Prediction, NOAA, Camp Spring, Maryland, USA
    3. Joint Center for Satellite Data Assimilation, Camp Springs, Maryland, USA
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  • Fuzhong Weng

    1. Center for Satellite Applications and Research, National Environmental Satellite, Data, and Information Service, NOAA, Camp Springs, Maryland, USA
    2. Joint Center for Satellite Data Assimilation, Camp Springs, Maryland, USA
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Abstract

[1] Special sensor microwave imager/sounder (SSMIS) on board the U. S. Defense Meteorology Satellite Program satellites includes six upper atmosphere sounding (UAS) channels for probing air temperature in the upper stratosphere and mesosphere. Three of the UAS channels 19–21 are sensitive to the Doppler frequency shift due to Earth's rotation. The sensitivity to the frequency shift in large degree depends on the O2 Zeeman splitting effect, which is a function of the Earth's magnetic field strength and the angle between the Earth's magnetic field and propagation direction of the electromagnetic wave. Since the brightness temperatures can change up to 2 K as a result of the Doppler shift, the fast radiative transfer model developed earlier for the SSMIS UAS channels has recently been improved to take the Doppler shift into account. In the fast model, an averaged transmittance within the channel frequency passbands is parameterized and trained with a line-by-line radiative transfer model that accurately computes the monochromatic transmittances at fine frequency steps within each passband. The model is evaluated by comparing it with the line-by-line model in an independent experiment. The root mean square differences between the two models are 0.21, 0.39, 0.34, and 0.19 K for channels 19–22, respectively. Using the model, the sensitivities of the radiances to the Doppler shift are analyzed through simulations. A theoretical explanation is given for the dependence of the sensitivities on the Zeeman splitting effect. Results from the analysis are then compared to the observations and a good agreement is achieved.

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