This height is calculated relative to an average elevation determined for the moon's surface, since there is no such thing as a "sea level" as a reference on the moon.
这个高度是对比月球表面平均高度后计算出来的,因为月球表面并没有“海平面”作为参照。
2
The height of a thing above a referencelevel, especially above sea level or above the earth's surface.