The US space agency satellite uses a laser altimeter to measure the elevation of the ice sheets.

BBC: Laser satellite records ice loss

The elevation measurements were collected by the Mars Orbiter Laser Altimeter (MOLA), an instrument aboard NASA's Mars Global Surveyor spacecraft, during the spring and summer of 1998.

BBC: By BBC News Online Science Editor Dr David Whitehouse

It has also scanned the surface of the planet using Mola (Mars Orbiter Laser Altimeter), which beams an infrared laser pulse towards the surface of the Red Planet 10 times a second.

BBC: New view of giant Martian volcano