WEBVTT FILE 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