The oblique sounding is one of the powerful tools, by which an obliqueionogram is obtained with the group path or time delay against operating frequency.
斜向探测是电离层探测的主要方式之一，它能够获得电波传播群时延和频率关系的电离图。
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An obliqueIonogram is a plot showing the group path or time delay against operating frequency when using swept frequency obliquely sounding between the transmitting and receiving site.