Evaluation of an Ambient HF Sky-Wave Propagation Model.
Topical rept. 1 Nov 77-31 Oct 78,
MISSION RESEARCH CORP SANTA BARBARA CA
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The ambient sky-wave propagation model in the HFNET computer program is evaluated by comparing predicted results with those from the widely used HFMUFES4 computer program and data from mid-latitude and auroral region propagation paths. The HFNET propagation model consists of two parts - a geometrical model and an ionospheric parameter model. The HFNET geometrical model uses the virtual height technique with corrections made for ionospheric tilts in and perpendicular to the great circle plane. Good agreement between results from HFNET and HFMUFES4 was obtained when the same ionospheric parameters for a horizontally uniform ionosphere were used in both programs. Comparison of program results with data from a 3,260 km mid-latitude propagation path showed good agreement, thereby establishing the validity of the goemetrical model. HFNET predictions were seen to depend upon models of ionospheric parameters. This dependence, of course, applies to all models of sky-wave propagation. HFNET allows the user to select one of two ionospheric models of median characteristics. One model is global in nature while the second model applies only to latitudes greater than about 45 degrees. Comparison of HFNET results using the global model with data from the mid-latitude path shows that the predicted MUF is 5 percent to 20 percent below the average of daily values obtained over a months time. However, the HFNET values are within the wide range of observed daily variability. For frequencies below the MUF, those generally used so as to avoid the problems associated with operating near the highly variable MUF, predicted and measured characteristics such as elevation angle and mode type are in good agreement.
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