Emergency HF Communication for the Philippines
Welcome to the USU Space Weather Center (SWC) site for providing global HF frequency availability for localities. Four figures are provided for the Near Vertical Incidence Skywave, or NVIS, radio-wave propagation conditions. The figures show maximum usable frequencies for NVIS in the range between 1.8 and 15 MHz. NVIS is most useful in mountainous areas where line-of-sight propagation at VHF or UHF frequencies is ineffective or when the communication distance is beyond ground-wave (more than 50 miles, 80 km) and less than sky-wave (300 to 1500 miles, 500 to 2500 km). The other ten figures show the real-time availability of HF across all frequencies. Both global and regional views are given for the real-time HF communication frequency availability.
How do we create our HF products maps? First, the SWC uses the GAIM (Global Assimilation of Ionospheric Measurements) system to produce a physics-based, data assimilation representation of the current global ionosphere. It is updated every 15 minutes with 10,000 global TEC measurements to produce the F region ionosphere. Next, the ABBYNormal model from Space Environment Corporation is separately run to produce the D-E region ionosphere. The two datasets are combined to accurately represent the effects of space weather (from solar flares and geomagnetic storms) upon the ionosphere. This real-time and forecast global ionosphere is used for ray-tracing and signal absorption calculations to propagate HF signal strengths. Both oblique and NVIS HF propagation maps are generated using the GAIM, ABBYNORMAL, and HF propagation models. The advantage of these SWC HF products is that alternate HF frequencies can easily be found for emergency uses, even during periods of very active space weather.