Noun
ionogram (plural ionograms)
English Wikipedia has an article on:ionogramWikipedia
A display of the data produced by an ionosonde; a graph of the virtual height of the ionosphere plotted against frequency.
Data from ionograms may be used to measure changes in the Earth's ionosphere due to space weather events.
Oblique sounders use a transmitter at one end of a given propagation path, and a synchronized receiver, usually with an oscilloscope-type display (ionogram), at the other end. Source: Internet
The ionogram display shows the effective altitude of the ionospheric layer as a function of frequency. Source: Internet