Mars Orbiter Laser Altimeter (MOLA)

Description

The Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor is designed to map the martian global topography and can also be used to measure the height of water and carbon dioxide clouds. This information will be used for scientific objectives including: 1) to study the surface processes on Mars, including the formation and evolution of volcanoes, basins, channels and the polar ice caps; 2) combined with gravity and other data, to study the structure and evolution of the interior of Mars, including the lithospheric thickness and strength, internal convection, composition, thermal history, and release of water and carbon dioxide to the surface; 3) to calculate the volume and seasonal changes in the polar ice deposits; and 4) to measure the altitude and distribution of water and carbon dioxide clouds, for the purpose of constraining the volatile budget in the martian atmosphere.

The MOLA works by transmitting a laser pulse down towards the surface. The pulse is reflected off the surface (or cloud) back to the instrument, where the return is detected. The two-way travel time is recorded, giving a measure of the distance between the spacecraft and the surface. Corrections are made to this distance based on atmospheric effects and accurate tracking of the spacecraft position allows an estimate of the surface altitude or cloud height. A large number of surface altimetry measurements will be taken, and combined to produce a global topographic map.

The MOLA consists of a diode pumped, Q-switched Nd:YAG laser transmitter with a pulse energy of 40-45 mJ. It can send continuous bursts of 10 pulses/sec, each pulse having a beam diameter of 1 cm and a divergence of 0.45 mrad. The reciever is a 50 cm parabolic antenna with a Si APD detector and four electronic filters (20, 60, 180, and 540 ns). The reciever field of view is 0.85 mrad with a 10 degree cone about the mirror exclusion. The vertical resolution is 2 m local (relative) and 30 m global (absolute). The horizontal resolution is 160 m. The altimeter is run by a 80C86 microprocessor with 54HC family logic. The altimeter is mounted to the Mars Global Surveyor instrument panel.