Maximum observed frequency in HF backscatter ionogram and day variblelaw of slope distance.
高频返回散射电离图中最高观测频率、斜距的日变化规律；
2
The oblique sounding is one of the powerful tools, by which an oblique ionogram 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。
3
An oblique Ionogram 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.