Institute for Telecommunication Sciences / Research / Radio Propagation Software / ITM / ITM

Irregular Terrain Model (ITM) (Longley-Rice) (20 MHz – 20 GHz)

Abstract: The ITS model of radio propagation for frequencies between 20 MHz and 20 GHz (the Longley-Rice model) (named for Anita Longley & Phil Rice, 1968) is a general purpose model that can be applied to a large variety of engineering problems. The model, which is based on electromagnetic theory and on statistical analyses of both terrain features and radio measurements, predicts the median attenuation of a radio signal as a function of distance and the variability of the signal in time and in space.

Description of the ITM/Longley-Rice Model

Adobe Acrobat formatted files (.pdf):

  • HuffordITMalgWhitePaper.pdf - The ITS Irregular Terrain Model, version 1.2.2 Algorithm.
  • Hufford_1985_Memo.pdf - Dr. George Hufford's 1985 Memo describing the changes to ITM version 1.2.1 (dated April, 1979) in ITM version 1.2.2 (dated September, 1984).
  • itm.pdf - The "definitive" representation of the ITS Irregular Terrain Model. It contains both the FORTRAN source code and a rather extensive documentation. Updated 5 Aug 2002 to fix missing functions (TeX to pdf conversion problem).

TeX formatted files (If unfamiliar with TeX, use the .pdf files above):

Zip file download contains the following files:

  • itm_alg.tex - The ITS Irregular Terrain Model, version 1.2.2 Algorithm, written in the TeX language. It is a stand-alone file, prepared for Plain TeX. It might be almost readable as is.
  • itm.tex, itm.cts, itm.mds, itm.ndx, fweb.sty, and fwebmac.sty - The documentation files for the programming of the ITM. This is written in the TeX language and should have the program TEX applied to it. As is, it is not very readable.

Available Software

Disclaimer: The ITM software was developed by NTIA. NTIA does not make any warranty of any kind, express, implied or statutory, including, without limitation, the implied warranty of merchantability, fitness for a particular purpose, non-infringement and data accuracy. NTIA does not warrant or make any representations regarding the use of the software or the results thereof, including but not limited to the correctness, accuracy, reliability or usefulness of the software or the results. You can use, copy, modify, and redistribute the NTIA-developed software upon your acceptance of these terms and conditions and upon your express agreement to provide appropriate acknowledgments of NTIA's ownership of and development of the software by keeping this exact text present in any copied or derivative works. By clicking the links on this page to access the software, you acknowledge that you have read this disclaimer.

Current ITM software, source code, and language bindings:

The active ITM GitHub repository contains the most current C++ code base as well as various wrappers packaged for ease of use.

Legacy FORTRAN and C++ source code and sample results:

A Public Archive on GitHub archives the legacy FORTRAN code and C++ version 1.2.2, both of which are no longer being actively developed.

For questions about the code, contact William ("Billy") Kozma.

For questions about ITM, contact Paul McKenna.