LOLA, the Lunar Orbiter Laser Altimeter aboard the Lunar Reconnaissance Orbiter spacecraft, is an instrument for measuring the altitude of the Moon's terrain. As LRO orbits the Moon, LOLA bounces laser light off the lunar surface 28 times per second. An array of five sensors arranged in an X-shape detects the reflected light. The amount of time it takes the light to travel to the surface and back to the sensors tells the instrument how far away the surface is. Over time, LOLA builds up a complete elevation map of the Moon.
This animation illustrates how the X-shaped LOLA sensor footprint travels over the lunar surface. The LOLA data track is taken from LRO orbit number 1155, on September 27, 2009, as the spacecraft passed over Amundsen crater near the lunar south pole. It begins with a distant view showing the entire crater, then switches to a view near the surface that chases the laser pulses over the central peak and across the floor of this large crater. Through most of the movie, the laser pulses are shown racing across the surface at actual speed, but at one point, the pace is slowed so that the viewer can see the sensor pattern of each individual laser pulse.
The imagery of the ground view is a high-resolution photograph taken by the LRO narrow-angle camera at the same time this LOLA data track was being recorded. The shape of the terrain in all of the views is taken from LOLA elevation maps. All of this data is publicly available from the Planetary Data System's LRO archive.