Typical calculations

This page contains a few applications using 4A/OP. 4A/OP processing is controlled by a set of global variables that identify required input data files and a file of run parameters. The user defines these variables through a script file or a Graphical User Interface (GUI).

  • Input data include algorithm fixed and user data.
  • Algorithm fixed input data provide information for:
    • Optical thickness atlases
    • Reference thermodynamical parameters used for the computation of atlases
    • Default gas mixing ratio
  • User input data are:
    • Atmospheric profiles (on user-defined pressure levels)
    • Spectral surface emissivity
      Click to view full-size image
    • Instrumental functions if it is necessary
      • Radiometer examples

        HIRS/NOAA-16 instrument function
        for selected IR channels

        MODIS/Aqua instrument function
        for selected IR channels
      • Interferometer / spectrometer examples

        AIRS instrument function
        for a set of wave numbers

        IASI1c instrument function
        for a given wave number
    • Simulation definition parameters
  • Output data depend on the simulation case. "Pseudo-infinite" case:
    • High resolution spectra (radiances and brightness temperatures)

    "Instrument" case:

    • Convolved spectra (radiances and brightness temperatures)
    • Jacobians on user-defined pressure layers (partial derivatives of the radiance with respect to the temperature, the gas mixing ratio and the surface emissivity)
    • Transmittances on user-defined pressure layers

Examples

The examples provide illustrations of both the input and output files. See the content of each input file for a description of simulation definition parameters. We present several examples of how to use 4A/OP.

  • Example 1

    As a first example, here is the high-resolution radiance (in equivalent brightness temperature) computed from 719 to 721 cm-1 for five TIGR standard profiles (see figures 1 and 2). The results are shown in figure 3. Figure 4 displays the same simulation conditions but for another spectral domain. Click here to see the input parameter file corresponding to the first spectral domain.

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    Figure 1
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    Figure 2
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    Figure 3
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    Figure 4
  • Example 2

    The second example is the computation of the convolved radiance (in equivalent brightness temperature) that would be measured by the instrument IASI (Figure 5), from 850 to 900 cm-1, and by HIRS (Figure 7) from 750 to 1000 cm-1. The corresponding Jacobians with respect to the temperature for IASI are illustrated in Figure 6. Click here to see the input parameter file corresponding to IASI.

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    Figure 5
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    Figure 6
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    Figure 7