When we investigate land cover using the instruments aboard
Landsat satellites, we collect sets of data for different wavelengths.
Some are in the infrared, and others correspond to blue, green, and
red visible light. We can combine any three of the images
to create different depictions of Earth's surface.
What you're seeing now is a Landsat image of Florida,
made with data from the blue, green, and red visible wavelengths.
We call this a "natural-color" image, because it looks
approximately what we would see with our naked eye, if we flew far above Florida.
But we could choose data
from other wavelengths, and map them to blue, green, and red colors
to highlight different features of the land surface.
With this particular depiction of the multi-spectral data,
for example, we can see much greater contrast between trees & shrubs and
sawgrass marsh, than was apparent in the natural-color image.
We call certain combinations of wavelengths "false-color" images,
because they do not replicate what we see with the naked eye.
Yet they allow us to create images where we can highlight or enhance different surface features.
The following depiction approximates the type of
image that you can get from color-infrared film.
It turns out that vegetation -
growing, active vegetation - reflects a lot of light in the near-infrared
and so areas with healthy, growing vegetation
jump out as red in these images.
You can easily distinguish the healthy agriculture more clearly
than you can in the true-color image.
Here you can look at the three different depictions of the
multi-spectral data we use to create these images
and you can see how the surface cover appears different with some features
enhanced in the different depictions.