LIDAR

LIDAR (Light Detection and Ranging) is an optical remote sensing technology that measures different properties of dispersed light to find range or other information of a distant target. The difference between lidar and radar is that lidar uses shorter wavelengths of the electromagnetic spectrum, generally close to infrared.
Here is a LIDAR image of lower Manhattan. It shows the height of the buildings in 3-D. You can see the height of the "rubble" from where the World Trade Centers fell. It helped with the plans of recovery.

http://www.noaanews.noaa.gov/stories/images/manhattan-lidar092701.jpg