Building and running 4A/OP

The 4A/OP distribution package is supplied in a single compressed tar file. The file is compressed using gzip, available at no cost from the Free Software Foundation. The 4A/OP source code is Fortran 90 and C compatible; it is contained within several files *.f90 and one file *.c . Generation of an executable is simply a matter of compiling these files with a F90 compiler and a C compiler under UNIX (Sun) or Linux operating systems.

The tar file also includes a Unix shell script, CasTest, that directs 4A/OP to produce output corresponding to some examples given in the page 4A/OP SOFTWARE / typical calculation section.

Also included in the tar file is the Reference Documentation, a plain text file that fully describes all input parameters.

The 4A/OP distribution package also contains a Graphical User Interface (GUI).

The computation time for a spectrum alone is reasonable but depends on the machine used. For Jacobians, it can take a long time to get results. The computation time is a function of the number of levels, the number of implied molecular species, the spectral resolution and the instrumental function for the convolution case. Here is some computing time examples for two different machines in the case of a IASI spectrum:

MachineIASI spectrum aloneIASI spectrum
+ 4 Jacobians
Linux Xeon 3.4 GHzAbout 28 secondsAbout 5 minutes
Unix Sun 900 MHzAbout 110 secondsAbout 30 minutes


The Reference Documentation (PDF format, 7.7 MB) is in the doc subdirectory of the main 4AOP directory. This file can be printed on a postscript printer. You should also be able to view it with the PDF viewer (Acrobat Reader).

The Reference Documentation contains the information needed to run 4A/OP. It also contains detailed description of the model components and built-in data.

quick start guide is also available to provide new users with a quick way inside the most common 4A/OP features.

The Graphical User Interface

The Graphical User Interface of 4A/OP is designed to assist new users in understanding the 4A model handling. The gui subdirectory of the distribution package contains the program files.

The programming language used to implement the GUI is TCL/TK (Tool Command Language / Tool Kit), version 8.4 and it uses the library BWidget.

The typical sequence of operations is to set the options, set the data, save the file, run 4A, and then view the results.

The user’s choices are presented through a notebook that displays several pages for each type of parameters. Examples of pages are described by the following screenshots.

4AOP GUI – General
4AOP GUI – Spectral conditions
4AOP GUI – Observation configuration
4AOP GUI – Molecules
4AOP GUI – Aerosol contribution