Signal Identification and Trace Extraction for the Vertical Ionogram

Vertical ionograms suffer from artifacts and distortion due to other users of the high-frequency channel and the ionosphere. The traces of each layer have variable shapes, so the automatic scaling of the vertical ionograms is rather complicated. New algorithms for signal identification and trace extraction are developed to support automatic scaling. Different features of the signals, such as signal-to-noise ratio, Doppler shift, and virtual height, are converted to certainty factors and combined to identify signals. Kalman filtering, which is widely used in trace extracting, is introduced to form traces and separate the ordinary trace and the extraordinary trace. These algorithms are effective without using information on the wave polarization and can be applied to the ionograms recorded by single-antenna systems.