As the basis of the tracking algorithm, an echo model is the key to radar altimeter design.
雷达高度计回波模型是设计、检验高度计跟踪算法的基础，是高度计设计的关键性环节。
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Laser altimeter not only can precisely measure the target distance, but also extract characteristic information, such as inclination, roughness etc. from its echo signals. So they are applied widely.