|This stylised diagram indicates the overall shape of the traces recorded by an ionosonde. The diagram is marked with the characteristic heights and frequencies which are often used to describe ionospheric features.|
From ionograms such as this it has been deduced
that there are several layers in the ionosphere, which may or may not be present
at a given time.
These have, for historical reasons, been named the E, F1 and F2 layers.
Click on the image for a better view
It is possible to determine a number of parameters from an ionogram for
each of these layers such as the height of the layer or the highest frequency
that a layer reflects (its penetration frequency or critical frequency).
This process of reading parameter values from ionograms is known as scaling, a method which was used to derive almost all information from the early, analogue ionosondes (Piggott and Rawer, 1972, 1978; Piggott, 1975; Wakai et al., 1986). Manual scaling is not performed on ionograms from the AIS. Instead, all the relevant echo information is stored in a digital form. However, some parameters, so-called AIS Key Parameters, are extracted automatically on a routine basis as part of the GGS (Global Geospace Science) project and transferred back to HQ on a weekly basis.
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