The best pictures of the Earth from space in 50 years: how Landsat satellites changed science

The best pictures of the Earth from space in 50 years: how Landsat satellites changed science

In July 1972, NASA launched a new Earth image satellite, Earth Resources Technology Satellite, which marked the launch of the NASA Landsat and Geological Survey of the United States of America, an ambitious project aimed at documenting the entire Earth from space, which continues to this day, 50 years later.

How did it start?

The first two satellites operated in four spectral ranges, or light waves: visible light in red and green and two nearby infrared ranges; the Middle infrared range allowed satellites to distinguish between vegetation and other land cover and assess the condition of flora; in turn, visible wave lengths distinguished bright surfaces, such as snow, deserts and clouds, from dark surfaces such as water; each scene occupied 185 km on one side.

The data from the first satellites were recorded on magnetic tapes of a huge size, and the loud broadband video recorders that flew on the first three satellites weighed 34 kg each, weighing almost 550 metres in length.

On the basis of these data, scientists generated and printed photographic images. These images provided a general picture of the location from the height of the bird's flight. However, the real strength of the data became apparent after computer algorithms helped researchers to better identify vegetation cover categories.

How many images have Landsat satellites made?

Since their debut, Landsat has collected more than 10 million images or scenes. These photos show more than real-time images of land and coasts. In combination with images of past years, they capture changes in time — slowly disappearing glaciers or urban spaces spread over the landscape.

Why do you need them?

These scenes and comparative images are used worldwide: hydrologists use them to track river changes; environmentalists use them to determine the extent of deforestation; farmers and agricultural organizations use them to analyse the state of crops.

During the five decades of Landsat's existence, eight different Landsat satellites have flown over the planet, and now three satellites continue to collect global observations from space: Landsat 7, 8 and 9. Landsat 9, the newest of the series, has come into orbit in the autumn of 2021.

What's next?

As Landsat continues to evolve, the people and projects that use it are also growing. Scientists and engineers are already looking forward to the next mission, and it is not for nothing: NASA and the U.S. Geological Survey are developing options for the next landsat iteration, which is still called Landsat Next.

According to scientists, Landsat's space observations have provided new opportunities for understanding a changing planet. "We can't all be astronauts. But looking at Landsat images, anyone can understand what the Earth looks like from space. This is a unique opportunity," scientists conclude.