Image above: LIDAR beam aboard the Mars Phoenix Polar Lander.
Image at left: Backscatter from LIDAR aimed into Martian fog.
LIDAR is a Light Detecting and Ranging Instrument mounted on the deck of the Rover. LIDAR data is available to the Mars Weather Scientist.
LIDAR works by sending out a beam of laser light, and detecting the return of light scattered by atmospheric particles. This 'backscattering' can indicate abundance of particles, types of compounds available, temperature and height of particles.
More information is available at Scientific Instruments, LIDAR.