Remote sensing, means to observe something from a distance. For Example; Satellites observe earth from space, and help scientists study large tracts/groups of land. Optical Remote Sensing satellites use reflected light, to determine and detect electromagnetic energy on The earth's surface.
This was the best I could do, I'm sorry if this doesn't help. Your question is very vague, which makes it hard to answer, seems how I don't know if it's an essay question, or multiple choice. I hope this helps you, even just a little bit! :)
