The leaves fell to the ground.
Koichi has a Secret Base 1km above ground.
When you look at Tokyo Tower from the ground it feels tremendously powerful.
Remember 地下, which is "below ground." Well, this is ground and above combined together, so I bet you can guess that this means above ground. But usually things above ground don't float (unless you're in space), so it's really on the ground.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.