Satellite imagery

Satellite images, also called Earth observation imagery or spaceborne photography, are pictures of our planet taken by special cameras on satellites orbiting above Earth. These satellites are run by different countries and companies, and they capture detailed views of our world from space.

These images are very important because they help us see big areas of Earth from above. We can use them to watch how forests grow, track changes in weather, and even monitor natural events like hurricanes or wildfires.

Many companies sell these satellite images to governments and businesses. For example, maps like Apple Maps and Google Maps use satellite pictures to show us roads, buildings, and landscapes from above. This helps us navigate and understand our world in new ways.

History

Further information: First images of Earth from space

The very first pictures of Earth from space were taken during flights that did not go all the way around the world. On October 24, 1946, the United States sent up a rocket called the V-2, which took a picture every 1.5 seconds. These pictures were taken from five times higher than any before. The first pictures from a satellite orbiting Earth were made on August 14, 1959, by the U.S. Explorer 6. In 1972, a famous picture called The Blue Marble was taken from space. That same year, the United States began the Landsat program, which has become the biggest effort to collect pictures of Earth from space. In 1977, the United States got the first live pictures from a satellite using the KH-11 system. The newest Landsat satellite, Landsat 9, was launched on September 27, 2021.

All the satellite pictures made by NASA are shared freely by the NASA Earth Observatory for everyone to see. Many other countries also have their own satellite picture programs, including a teamwork effort by Europe with the ERS and Envisat satellites. Today, there are companies that sell pictures from satellites, and many people can easily access these pictures thanks to software made by different companies and groups.

Applications

Satellite images are very useful in many areas. They help weather experts predict the weather, track big storms, and study climate change. They also help scientists learn about the oceans by measuring sea temperatures and watching sea life.

These images help farmers and fishermen by showing where fish are and how healthy crops are. They are important for protecting wildlife by mapping where animals live and watching changes in nature. Satellite images also help take care of forests by tracking where trees are being cut down and watching for fires. They even help plan cities by showing how land is used.

Satellite images can use many kinds of light, like the light we see and special kinds of light we cannot see. This helps scientists learn more about our world.

Usage

Satellite images are used in many different areas, such as farming, studying Earth’s water and land, protecting forests, planning cities, teaching, and even for safety and protection. These images can be taken in many types of light, including the parts we can see and others we cannot, like infrared light. Special maps can also be made using radar.

Today, computers help read and understand these images more easily. In the past, some of this work was done by special companies for the government. For example, one company helped create early methods to improve digital images.

People also use satellite images to help take care of the environment. In some places, they have found unauthorized waste sites. In France, satellite pictures have helped find private swimming pools to make sure proper taxes are paid.

Anyone can buy these images to learn more about what is happening in the world. For example, they have been used to see old military equipment that might be used again in conflicts.

Disadvantages

Satellite images of Earth can be very large because the planet is huge and the pictures need to be detailed. This means it takes a lot of time to turn the raw data into useful images. Sometimes, extra steps are needed to fix issues like stripes in the pictures. Weather can also affect the quality, especially in places with lots of clouds.

Companies that take satellite pictures usually don’t give them away for free. Instead, you need a special permission, called a license, to use their images. This makes it harder to create new things from these pictures. Some people worry about their privacy because these images can show their property from above. Google Maps says their images are just like what anyone could see if they flew over or drove by a place.

Data characteristics

Satellite images come in different qualities, called resolutions. There are five main types of resolution: spatial, spectral, temporal, radiometric, and geometric.

• Spatial resolution tells us the size of each pixel in the image. It shows how much of the Earth's surface each picture piece covers.
• Spectral resolution is about the different colors and wavelengths the satellite can see.
• Temporal resolution is how often the satellite takes pictures of the same place.
• Radiometric resolution is how well the satellite can see differences in brightness.
• Geometric resolution is how well the satellite can show small details on the ground. For example, some satellites can see objects as small as 41 centimeters.

Imaging satellites

Further information: Earth observing satellites

Many countries have their own satellite imaging programs because these images are useful for many reasons. The United States shares its data freely for science. Some important programs include:

Public domain

The CORONA program was a series of American satellites made by the Central Intelligence Agency and the U.S. Air Force. It used special cameras to take detailed pictures from space.

Landsat is the oldest continuing program for watching Earth from space. It has taken pictures since the 1980s, showing changes on our planet.

MODIS takes pictures of Earth almost every day in many different colors of light, helping scientists study our world.

The Sentinel satellites are being developed to help with many tasks, like watching land and water.

ASTER is a tool on a NASA satellite that creates maps showing land temperature, elevation, and more.

Meteosat satellites watch the weather over Europe and Africa.

Himawari satellites watch weather over Asia and the Pacific Ocean, giving updates every few minutes.

Private domain

Private companies also launch satellites to take pictures of Earth for many uses.

GeoEye has a satellite that can see objects as small as about half a meter from space.

Maxar operates satellites like WorldView that can see very small details on the ground.

Airbus Intelligence has satellites called Pléiades that take extremely clear pictures for both government and business uses.

Spot Image provides pictures from several satellites, including SPOT, which can see details as small as one and a half meters.

Planet Labs runs many small satellites called Dove and SkySat that take pictures for environmental monitoring, farming, and more.

ImageSat International has EROS satellites that take very clear pictures for government and business uses around the world.

China Siwei operates GaoJing-1 satellites that take detailed pictures for mapping and monitoring.