The dynasonde at Halley remotely senses the structure and motion of plasma 60-500 km
up in the ionosphere and within a horizontal radius of about 500 km.
The structure of the ionosphere is affected by ultra-violet and X-ray radiation
from the Sun and by charged particle precipitation from
geospace which also causes the aurora.
The picture shows a real ionogram measured at Halley. It is a plot of the
virtual height of a radio reflection as a
function of the transmitted frequency.
Each measurement is colour-coded according to another one of the