Apollo 15 Mission
Science Experiments - Laser Altimeter
The Laser Altimeter measured the heights of lunar surface features
The Laser Altimeter Experiment was performed on Apollo 15, 16, and 17. In this experiment, a pulse from a laser was aimed at the lunar surface. The reflection of the pulse from the surface was then observed with a small telescope. The length of time the pulse took to travel from the spacecraft to the Moon and back is related to the height of the spacecraft above the surface of the Moon. Measurements were made roughly every 30 kilometers across the Moon's surface. These measurements are sufficiently accurate to distinguish height variations of 10 meters between adjacent measurement points. On Apollo 15, measurements were obtained for a total of 4 1/2 orbits.
This figure shows an example of the results from this experiment. The nearside is shown on top and the farside on the bottom. All elevations are shown relative to the Moon's average radius of 1738 kilometers. Mare regions such as Oceanus Procellarum and Mare Serenitatis are typically several kilometers lower than the surrounding highlands. Mare regions also tend to be much smoother than the highlands. The farside tends to be both higher and rougher than the nearside.