A Simple Method for Visualizing the NVIS Open Channel Based on Ionogram

To guarantee the success of radio wave propagation, the determination of carrier frequency (f
c
) in Near Vertical Incidence Skywave (NVIS) communication system is based on the information of ionosphere opening channel that varies over time. The open channel information could be obtained from the Ionosonde data or ionogram, which provides the ionosphere parameters, such as minimum frequency (f
min
) and critical frequency (f
o
) as the lower and upper bound of f
c
. However, to obtain f
min
and f
o
values from ionogram, the process are complex and tends could only be done precisely by manual scaling process, especially when the ionogram is unclear and noisy. In this paper we discuss a simple method for visualizing the opening channel of ionosphere using ionogram data. The echo signal sounding for each frequency were counted to show the reflected frequencies as the opening channel information for NVIS communication system.