1 00:00:00,100 --> 00:00:03,550 When we investigate land cover using the instruments aboard 2 00:00:03,570 --> 00:00:08,110 Landsat satellites, we collect sets of data for different wavelengths. 3 00:00:08,130 --> 00:00:12,130 Some are in the infrared, and others correspond to blue, green, and 4 00:00:12,150 --> 00:00:16,170 red visible light. We can combine any three of the images 5 00:00:16,190 --> 00:00:20,190 to create different depictions of Earth's surface. 6 00:00:20,210 --> 00:00:24,230 What you're seeing now is a Landsat image of Florida, 7 00:00:24,250 --> 00:00:28,250 made with data from the blue, green, and red visible wavelengths. 8 00:00:28,270 --> 00:00:32,280 We call this a "natural-color" image, because it looks 9 00:00:32,300 --> 00:00:40,360 approximately what we would see with our naked eye, if we flew far above Florida. 10 00:00:40,380 --> 00:00:44,420 11 00:00:44,440 --> 00:00:50,490 12 00:00:50,510 --> 00:00:52,530 But we could choose data 13 00:00:52,550 --> 00:00:56,550 from other wavelengths, and map them to blue, green, and red colors 14 00:00:56,570 --> 00:01:00,570 to highlight different features of the land surface. 15 00:01:00,590 --> 00:01:04,600 16 00:01:04,620 --> 00:01:08,630 17 00:01:08,650 --> 00:01:12,640 With this particular depiction of the multi-spectral data, 18 00:01:12,660 --> 00:01:17,930 for example, we can see much greater contrast between trees & shrubs and 19 00:01:17,950 --> 00:01:21,810 sawgrass marsh, than was apparent in the natural-color image. 20 00:01:21,830 --> 00:01:22,880 21 00:01:22,900 --> 00:01:27,920 We call certain combinations of wavelengths "false-color" images, 22 00:01:27,940 --> 00:01:31,480 because they do not replicate what we see with the naked eye. 23 00:01:31,500 --> 00:01:37,030 Yet they allow us to create images where we can highlight or enhance different surface features. 24 00:01:37,050 --> 00:01:42,050 25 00:01:42,070 --> 00:01:45,060 The following depiction approximates the type of 26 00:01:45,080 --> 00:01:50,080 image that you can get from color-infrared film. 27 00:01:50,100 --> 00:01:53,150 It turns out that vegetation - 28 00:01:53,170 --> 00:01:57,210 growing, active vegetation - reflects a lot of light in the near-infrared 29 00:01:57,230 --> 00:02:01,280 and so areas with healthy, growing vegetation 30 00:02:01,300 --> 00:02:07,340 jump out as red in these images. 31 00:02:07,360 --> 00:02:09,400 32 00:02:09,420 --> 00:02:13,440 You can easily distinguish the healthy agriculture more clearly 33 00:02:13,460 --> 00:02:18,090 than you can in the true-color image. 34 00:02:18,110 --> 00:02:21,530 Here you can look at the three different depictions of the 35 00:02:21,550 --> 00:02:25,560 multi-spectral data we use to create these images 36 00:02:25,580 --> 00:02:29,570 and you can see how the surface cover appears different with some features 37 00:02:29,590 --> 00:02:37,710 enhanced in the different depictions. 38 00:02:37,730 --> 00:02:56,356