||Example ionogram produced by the Halley dynasonde on 26
March 1994 at 23:10 UT. The F-region is shown by a clear O-mode (red) and
X-mode (green) trace starting at 240km, although "spread-F" conditions are
also evident indicating horizontal structure in the electron density. A
"second hop" is seen starting at 480km suggesting that the main trace is
situated overhead at Halley. Less well-defined traces are seen between 300km
and 450km resulting from off-vertical echoes and multiple reflections.