Institute for Telecommunication Sciences / Software / IF-77 Electromagnetic Wave Propagation Model (Gierhart-Johnson)

IF-77 Electromagnetic Wave Propagation Model (Gierhart-Johnson)

In 1973, ITS released the IF-73 (ITS-FAA-1973) air/ground propagation model developed for the Federal Aviation Administration (FAA). IF-73 evolved into the IF-77 (ITS-FAA-1977) model, which is applicable to air/air, air/ground, air/satellite, ground/ground, and ground/satellite paths. The IF-77 was incorporated into a number of FORTRAN programs that are useful in estimating the service coverage of radio systems. These programs may be used to obtain a wide variety of computer-generated microfilm plots.

The IF-77 propagation model is applicable to air/ground, air/air, ground/satellite, and air/satellite paths. It can also be used for ground/ground paths that are line-of-sight or smooth earth. Model applications are restricted to telecommunication systems operating at radio frequencies from about 0.1 to 20 GHz with antenna heights greater than 0.5 m. In addition, radio-horizon elevations must be less than the elevation of the higher antenna. The radio horizon for the higher antenna is taken either as a common horizon with the lower antenna or as a smooth earth horizon with the same elevation as the lower antenna effective reflecting plane.

The work was performed under contract to the U.S. Department of Transportation (DOT), contract number DTFA01-82-Y-10539 and published in the report:

• M.E. Johnson and G.D. Gierhart, The IF-77 Electromagnetic Wave Propagation Model, NTIA Sponsor Report FAA-ES-83/3, September 1983.

The IF-77 software is available at  https://github.com/NTIA/if77-gierhart-johnson. There you will find:

• The following updated FORTRAN source files:
  • Source file for ata.for
  • Source file for aalos.for
  • Source file for amsc.for
  • Source file for asorp.for
• Release v1.0.1 (Apr 20, 2019): This is essentially the original, legacy compiled and released source and binaries, but it fixes an issue with the original code that caused the application to fail if a frequency between 3.0 and 3.4 GHz was entered when running IF-77. It also contains a Windows 10 supported executable in place of the Windows 7 executable.
• Original Release: This is the original, legacy compiled and released source and binaries. The zip package contains:
  • ata.exe: An executable file for ATA that runs on a PC under DOS
  • atoa.in: Sample input file for ATA. Run with: ata < atoa.in > atoa.out
  • atoa.out: Sample output file for ATA.
  • cards.txt: Text description of data input cards.
  • Source file for ata.for
  • Source file for aalos.for
  • Source file for amsc.for
  • Source file for asorp.for
  • if77_intel.exe: In response to changing times, this executable was developed to run on a Windows 7, 64-bit machine. It was tested at ITS when it was created, but is deprecated and no longer supported. Source code is not provided for this executable.

Extensive comparisons of IF-77 predictions with measured data were made, and an atlas of basic transmission loss predictions was generated using the model. The following publications provide additional information:

• M.E. Johnson and G.D. Gierhart, Applications Guide for Propagation and Interference Analysis Computer Programs (0.1 to 20 GHz), NTIA Sponsor Report FAA-RD-77-60, March 1978
• M. E. Johnson and G. D. Gierhart, " Aerospace Propagation Prediction Capabilities Associated with the IF-77 Model," in Conference Proceedings: Operational Modelling of the Aerospace Propagation Environment, North Atlantic Treaty Organization (NATO), Advisory Group for Aerospace Research and Development (AGARD), Neuilly-sur-Seine (France), vol. 2, no. 238, November 1978
• M.E. Johnson and G.D. Gierhart, Comparison of Measured Data with IF-77 Propagation Model Predictions, NTIA Sponsor Report FAA-RD-79-9, August 1979
• M.E. Johnson and G.D. Gierhart, An Atlas of Basic Transmission Loss For 0.125 to 15.5 GHz, NTIA Sponsor Report FAA-RD-80-1, August 1980
• Weiner, M., Use of the Longley-Rice and Johnson-Gierhart Tropospheric Radio Propagation Programs: 0.02-20 GHz, IEEE Journal on Selected Areas in Communications, vol.4, no.2, pp. 297-307, March 1986

For technical questions about IF-77, contact Paul McKenna, (303) 497-3474, pmckenna@ntia.gov.