Thus, while it can easily discover suspect behavior on the earth's surface, a thorough scrutiny of the area in question would also require aerial photographs or on-site investigation. Yet these images remain very useful.
打個比方，它很容易查出地面上的可疑份子；但要做地毯式的搜索，就需配合精密度比較高的航空照片或實地測量做輔助。