While the video is long he does a pretty good job of explaining how radar works. I was a radar tech in the USAF and some of it went over my head. Anyway the simple is the satellites shoot a signal down and it reelects back up to the antenna. All the satellites create a huge antenna array that can create 3d images of the ground in real time. Couple that with other types of data and we could be found just about anywhere at anytime.