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:

  1. Optical thickness atlases
  2. Reference thermodynamical parameters used for the computation of atlases
  3. Default gas mixing ratio

User input data are:

Mixing ratio H2O
Mixing ratio O3
  • Spectral surface emissivity
  • 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
  • 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


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.

Figure 1
Figure 2
Figure 3
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.

Figure 5
Figure 6
Figure 7