They use a multimillion-dollar machine known as the Meisterbock gauge that laser-scans the entire surface of the vehicle for defects as small as a few millimeters.

WSJ: New Chrysler Battling Old Defects

Satellites have long been used to track ice extent (area), but calculating the thickness of the marine floes requires the overflying spacecraft to gauge the difference between the top of the ice surface and the top of the water - a relatively simple calculation then gives the overall volume.

BBC: Launch success for Esa's Cryosat-2 ice mission