Where does it come from? Each province has a remote sensing center. If you need free images in different time periods, unless you have acquaintances, you are basically charged. If there is no charge, you can ask the teacher if there is one. Teachers should have sufficient resources.

Outline:

I. Regional overview (geography, time)

Second, technical means to participate in monitoring.

Three. Detailed comparison of different time periods (area, vegetation coverage, vegetation growth, etc.). )

Vegetation coverage map of different periods on the same map (achievement map)