Before the advent of the space age, scientists generally believed that very little detail of the Earth could be seen from altitudes above 100 miles (161 km). Astronaut Gordon Cooper shattered that idea when he reported seeing roads, buildings, and even smoke from chimneys during his flight in a Mercury capsule in May 1963. Later observations used multi-spectral imagery in visible light and infra-red cameras, which made it possible to detect small variations of energy that features on the Earth's surface emit or reflect from the Sun. Vegetation could be distinguished from rock, soil, or water. It was easy to tell the difference between healthy and diseased crops, healthy or poor soil conditions, wet or dry soil, and even the difference between various crops under cultivation.

The first satellites to carry out detailed observations of the earth were the Landsats developed by General Electric for NASA. First...