A New View of Earth

How can scientists see changes across a forest that stretches farther than the eye can see? One answer is to look from space.

On July 23, 1972, NASA launched a satellite now known as Landsat 1. As it traveled around Earth, its instruments collected images of the land below. Unlike a single photograph, repeated images could show the same region at different times. Scientists could compare them to look for changes.

Landsat 1 carried a scanner that measured light reflected from Earth’s surface. It detected several ranges, or bands, of light. Some were visible to human eyes, while others were infrared, a kind of light people cannot see. Healthy plants reflect infrared light differently from water and many other surfaces. By studying the measurements, scientists could tell different kinds of land cover apart.

Imagine comparing two images of a forest taken years apart. If a large area that once appeared forested looks different in the later image, researchers might investigate whether trees were removed or a fire occurred. Images alone may not explain every change, so scientists can use other information to check their ideas.

Landsat images have helped people study crops, forests, water, and other features across broad areas. They were designed to observe the environment, not to identify individual people. Landsat 1 began a lasting record of Earth’s land, giving scientists a way to see how landscapes change over time.