1 00:00:08,250 --> 00:00:04,120 [silence] 2 00:00:08,270 --> 00:00:12,370 [music] Narrator: If you wanted to find out how 3 00:00:12,390 --> 00:00:16,490 tall mountains are on other planets, how would you do it? If you're on Earth, it's easy. 4 00:00:16,510 --> 00:00:20,590 You can take a picture, fly over the mountain, fly over the mountain, or 5 00:00:20,610 --> 00:00:24,660 you can actually go there and measure how high it is. On other planets, it's much 6 00:00:24,680 --> 00:00:28,740 more difficult. You might be able to estimate height using shadows, or even take 7 00:00:28,760 --> 00:00:32,780 3D pictures from a satellite. But what if you wanted to know what the mountain looked like as a 3D 8 00:00:32,800 --> 00:00:36,810 model? To find out, NASA scientists can use a precise measuring tool called 9 00:00:36,830 --> 00:00:40,830 LIDAR. Mounted on a satellite orbiting high above a planet, LIDAR instruments 10 00:00:40,850 --> 00:00:44,860 are able to accurately measure the distance between the instrument and the landscape below using 11 00:00:44,880 --> 00:00:49,020 laser pulses. To make these measurements, the LIDAR instrument first sends a laser 12 00:00:49,040 --> 00:00:53,170 pulse down to the planet's surface. The pulse hits the ground and reflects back to the 13 00:00:53,190 --> 00:00:57,290 instrument, where an onboard computer measures the time it took the pulse to make its trip. That 14 00:00:57,310 --> 00:01:01,380 gives a precise measurement between the instrument and the ground--with respect to the planet's 15 00:01:01,400 --> 00:01:05,470 gravitational center. As the satellite passes over the landscape, the instrument 16 00:01:05,490 --> 00:01:09,560 sends out a series of regular pulses. By recording and combining these measurements, 17 00:01:09,580 --> 00:01:13,620 scientists can use the instrument to gradually build up a map of the height of the terrain. 18 00:01:13,640 --> 00:01:17,680 After many more measurements, the end result is a high-resolution 19 00:01:17,700 --> 00:01:21,720 3D model that scientists can view as if they were actually on the planet, flying over the terrain. 20 00:01:21,740 --> 00:01:25,740 They can then study its shape in more detail, looking for clues to the relative 21 00:01:25,760 --> 00:01:29,760 ages of craters, the shape of valleys and landscape features, and much more. 22 00:01:29,780 --> 00:01:33,900 But LIDAR is far more versatile than simply measuring the shapes of mountains and craters. 23 00:01:33,920 --> 00:01:38,020 Earth scientists, for example, use LIDAR to measure the height and density of the Earth's forests. 24 00:01:38,040 --> 00:01:42,120 Others use LIDAR to study small changes in the heights of the Earth's major icecaps 25 00:01:42,140 --> 00:01:46,210 over time. Still other scientists use LIDAR to study the composition and structure of Earth's 26 00:01:46,230 --> 00:01:50,320 atmosphere, as well as the atmosphere of other planets. And they can do all 27 00:01:50,340 --> 00:01:54,410 that without ever having to climb a mountain. 28 00:01:54,430 --> 00:01:58,480 [rumbling]