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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.

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 download the software, you acknowledge that you have read this disclaimer.

Description of the ITM/Longley-Rice Model:

Adobe Acrobat formatted files (.pdf):

  • itm_alg.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 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.

FORTRAN source code and sample results:

Zip file download contains the following files:

  • itm.for - The source code for the ITM subroutines.
  • itm_man.txt - A manual for ITM. A straight ASCII file intended to aid the programmer in preparing a main program that involves the ITM.
  • uarea.for - "User's Area model," to illustrate one way to use the ITM in the area prediction mode. It is interactive with output directed to a file of the user's choice. This is the source code for the main program.
  • uarea.exe - An executable file for UAREA. Runs on a PC under DOS.
  • uarea_man.txt - A manual for UAREA. A straight ASCII file.
  • qkpfl.for - "Quick Profile," to illustrate one way to use the ITM in the point-to-point mode. It was written for batch processing on a mainframe computer, but may be run on a PC by redirecting input and output. This is the source code for the main program.
  • qkpflman.txt - A manual for QKPFL. A straight ASCII file.
  • qkpfl.exe - An executable file for QKPFL. Runs on a PC under DOS.
  • qkpfl32.exe- An executable file for QKPFL. Runs on a PC under DOS (in 32-bit mode).
    • You will need to put salflibc.dll into your C:\WINDOWS\SYSTEM directory for it to work.
  • qkpflbat.txt, qkpfldat.txt, and qkpflanx.txt - A sample showing how to run QKPFL on a PC-a batch file which runs the program using QKPFL.DAT as input and writing output to QKPFL.ANS. When run, the latter may be compared with QKPFL.ANX. Files should be renamed to QKPFL.BAT, QKPFL.DAT, and QKPFL.ANX. The .txt suffix was used to make it possible to easily view the files before running them.

C ++ source code is now available:

Zip file download contains the following files:

  • ITMDLL.cpp (Updated 06/26/07)
  • ITMsetup.exe - An executable file for ITM (C++ version) using the GLOBE terrain database (You must download this separately).
  • To see more information about GLOBE, see our GLOBE extraction routines.
  • Runs on a PC under Windows.
  • For questions about the C++ code, contact NTIA/OSM for support:

For information contact Paul McKenna.