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XRTM (X Radiative Transfer Model) is a plane-parallel multi-layer scalar/vector radiative transfer model with support for absorption, emission, and multiple scattering with the option for solar and/or thermal sources. In addition to the radiances or Stokes vector elements, XRTM can analytically generate derivatives of these quantities with respect to model inputs. XRTM implements several different radiative transfer solvers, is coded with speed in mind, and provides interfaces for C, C++, Fortran 77, Fortran 90, IDL, and Python, while the core library is coded in C. XRTM is free and open source software and is licensed under the GNU General Public License.


January 31, 2020

Version 0.92 is available for download with many new features and IDL and Python interfaces.


The following is a list of some XRTM's more interesting features:

See the following implementation table for supported options and outputs for each solution. See the documentation to decode the solution and option names.


The source code can be downloaded for Linux/Unix/MacOS as xrtm-0.92.tar.gz or for Windows as xrtm-0.92.zip.

Alternatively, the XRTM git repository may also be accesed on github.

See the user manual for documentation on how to compile the library and link it to your programs.


The XRTM manual can be read online as an HTML document or may be downloaded as a PDF. Alternatively, the XRTM distribution comes with both the HTML and PDF forms of this documentation in the "doc/" subdirectory.

The "examples/" subdirectory contains simple example programs that call XRTM and use some of its basic features. An example exist for each of the language interfaces supported.


For bugs, comments, or suggestions please email Greg McGarragh: greg.mcgarragh@colostate.edu.

Bug reports are greatly appreciated! If you would like to report a bug please include sample code that reproduces the bug, along with the inputs and expected outputs.