Ionospheric foF2 Map
A feature of the ionosphere is its ability to reflect radio waves. However, only radio waves within a certain frequency range will be reflected and this range varies with a number of factors.
The most widely used instrument for ionospheric measurement is the ionosonde. The ionosonde is essentially a high frequency radar which sends short pulses of radio energy into the ionosphere. If the radio frequency is not too high, the pulses are reflected back to earth.
The ionosonde records the time delay between transmission and reception of the pulses. By varying the frequency of the pulses (typically 1-22 MHz), a record is obtained of the time delay at different frequencies. This record is referred to as an ionogram.
The highest (see note) frequency which the ionosphere will reflect vertically is called foF2. These foF2 measurements from various sites can be used to create a map of foF2.
The above map can be used as a guide to NVIS ionospheric frequency support.
The map is updated at 15-minute intervals from 9 minutes past the hour. The offset from the hour allows for data acquisition from the IPS ionosonde network.
Note: The geomagnetic field splits a radio wave in the ionosphere into two separate components, termed the ordinary (o) and extraordinary (x) waves. It is the o-wave which is routinely scaled from ionograms.
Ionospheric F-layer Height (daytime hF2 and night time hF) Map (Experimental)
In addition to ionospheric frequencies the ionosonde also records the "virtual heights" of different layers in the ionosphere. They are called "virtual heights" as the radio pulse is assumed to travel at a constant speed, when in fact it slows near the critical frequency of the layer. Corrected heights are referred to as "true heights". "Virtual heights" are obtained from the time of flight of the transmitted radio pulse from transmitter, ionospheric reflection and back to the receiver. The map below shows the "virtual heights" of the F-layer of the ionosphere which has been obtained from the automatic interpretation of ionograms from the IPS network of ionosondes known as IPSNET. Ionospheric disturbances affect not only the frequency of support of the ionosphere but can also cause variations in heights of layers in the ionosphere. This can impact HF radio propagation prediction, if the actual reflection height of the radio wave is different from the assumed quiet ionosphere reflection height.
The data presented on this page are experimental and are derived from the automated interpretation of regional ionograms.