Manually scaling ionograms measured by Icheon and Jeju ionosondes over a 2-year period (2017–2018)

From 1966 until 2009, the ionosonde at the Anyang station has been monitoring the ionosphere over the Korea, Peninsula, and the ionosondes at the Icheon (37.14° N, 127.54° E) and the Jeju (33.43° N, 126.30° E) stations have continued their monitoring missions since 2010 and 2009, respectively. An ionosonde transmits HF radio waves vertically and records the waves reflected from the ionosphere on an ionogram. Ionospheric parameters, such as foF2 (the critical frequency of the F2 layer) and hmF2 (the peak height of the F2 layer), can be extracted from an ionogram using an automatic scaling program. However, an automatic scaling program may result in absurdly inaccurate ionospheric parameters. In this study, we manually scaled total 33,679 ionograms measured at the Icheon and the Jeju ionosondes for 2 years (2017 and 2018). By adopting the manual scaling method from the standard handbook of Wakai et al. (Radio Research Laboratory, Ministry of Posts and Telecommunication, Japan, 1987), we extracted five ionospheric parameters, namely foF2 , hmF2 , foE (the critical frequency of the E layer), hmE (the peak height of the E layer), and foEs (the critical frequency of the sporadic E layer), and compared them with the automatically scaled values obtained by using ARTIST5002 (the built-in automatic scaling program). We found that the automatic scaling software misinterpreted about 23% and 36% the ionograms taken at the Icheon and the Jeju stations, respectively, thus inaccurately characterizing both the ionospheric E and F layers. We classified those misinterpreted ionograms into eight cases: five cases about the F layer and three cases about the E layer. We discuss the reliability of automatically scaled parameters, emphasizing the need for manual scaling when scientifically investigating the ionosphere with ionosonde data. The manually scaled parameters can be used as “true” values when a deep learning model is trained to interpret measured ionograms.