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 </