What These Maps Show:These maps predict problem areas for radio communications between satellites and ground stations. The signals from the satellites must pass through the ionosphere. But the ionosphere contains significant regions of turbulence. Radio signals passing through these regions are disrupted. Their amplitudes vary irregularly and their phase and direction can also be affected. Important information can be lost and critical communications can be interrupted. The equatorial and high-latitude ionospheres are trouble spots where turbulence frequently develops. Understanding and predicting turbulent regions and their effects on satellite communications has important applications for military operations in remote locations, planned networks of mobile communications satellites, high-precision applications of the GPS (global positioning satellites) Network, and many others.
Two Different Types of Prediction Maps:
- Equatorial Maps: These maps provide contour lines giving the probability that moderate to severe signal disruption will occur if the line-of-sight path of the radio signal passes through a turbulent region while moving between the satellite and a ground station at a given location. The forecasts are based on climatology and have similarity to forecasts issued by the National Weather Service for thunderstorm/tornado activity. They are not snapshots, in space and time, of regions of irregularities. These maps find their application mainly for geosynchronous satellites that spend all of their time orbiting over the low-latitude ionosphere at a radial distance of 6.6 Earth radii. Because they orbit at the same rate that the Earth rotates, they appear suspended over roughly the same location on the Earth all the time. Radio signals from these satellites do not pass through the ionosphere vertically below the spacecraft but take various paths depending on the relative position of the satellite and ground station. Hence the location of the satellite is very important in these maps and is indicated by a black star. There would be a different prediction map for each different satellite location.
- High-Latitude Maps: These are maps of the strength of irregularities summed over altitude. They find their application mainly in providing warnings for polar-orbiting satellites in low-Earth orbit. The radio signals from these spacecraft pass vertically downward through the ionosphere to ground stations (hence the summation of irregularity strength over altitude). The amount of signal disruption is related to the strength of the irregularities.