The first images taken from space were from suborbital flights in the 1940s, and the first satellite image was taken in 1959 by Explorer 6. Satellite imaging is the use of satellites to collect data about the Earth via orbiting satellites or very high-altitude aircraft.

Satellite imaging has come a long way since then. There are now over 2,000 satellites in orbit around the Earth, and many different kinds with varying capabilities. Satellite imaging has uses in meteorology, conservation, geology, agriculture, cartography, education, intelligence, warfare, and more.

This article will cover some of the technology behind satellite imaging, how it works, and what it can be used for.

How Does Satellite Imaging Work?

Satellite orbiting Earth

Satellite imaging is a broad subject. There are different kinds of sensors and different methods for acquiring satellite images. Here are some of the ways that satellites and their sensors can vary.

Passive vs. Active Sensing

There are two broad categories of imaging satellites’ sensors. These are active sensors and passive sensors. Passive sensor satellites collect data about the Earth via electromagnetic radiation that is emitted by the sun and reflects off the Earth. On the other hand, active sensor satellites emit their own radiation and analyze it as it reflects back to the satellite.

Sensor Resolution

Like a normal camera, different satellite sensors have different capabilities. Every sensor will have a certain spatial resolution. This is basically how much area is able to be captured by the sensor at a time, or how many and how small its pixels are. Some sensors are able to capture a resolution of up to 0.31 meters squared per pixel, though most will not have a resolution that fine.

Keep in mind that satellites are constantly in motion. That means that in order to capture images of a broad area, either the sensor must be able to move or there must be an array of sensors. For instance, if the satellite is orbiting north-to-south, it may have a sensor or mirror that moves in the opposite direction to “scan” a broader area as it moves.

Photo of a satellite above clouds in space

The spectral resolution, on the other hand, is what kinds of light the sensor can capture. Different structures on Earth reflect electromagnetic radiation differently, which is what allows satellites to be so useful. Electromagnetic radiation includes visible light (like we see through our eyes), infrared, and ultraviolet light. For instance, snow reflects all radiation quite strongly, whereas dense vegetation will absorb a lot of red light but emit infrared light.

In this way, a satellite featuring sensors that can capture visible and infrared light will be able to differentiate between different environments on the planet’s surface. But this isn’t all satellites are able to do.

Unlike normal cameras, satellites also have temporal resolution. This refers to the amount of time between images for a particular location. If a satellite is being used to monitor a certain area, it will take a certain number of hours for the satellite to reach that location over the Earth again.

So, you can see that satellites are highly specialized pieces of equipment. Each satellite will be produced with a specific task in mind (or multiple tasks).

Image Processing

Due to the size of the Earth, the nature of imaging sensors, and the pure volume of images that need to be taken, image processing is required to make useful images.

One example is image stitching. Regardless of sensor size, for high-resolution images to be taken of large areas, several images will have to be taken. These will then need to be “stitched” together (luckily software does this almost seamlessly now) in order to create a single, larger image.

Because of radiation, satellite images often feature artifacts like stripes or streaks. Image de-striping is the process of removing these to create better images.

Further, depending on the use of the images, individual regions may have to be re-imaged depending on cloud cover or other obstructions to the shot. This is where temporal resolution comes in, and why it can require thousands of hours of sifting through images to create an ideal map of an area.

What Is Satellite Imaging Used For?

As we mentioned, satellite imaging has a wide range of uses. These include cartography and navigation, city planning, weather prediction, ecological surveillance, and military surveillance. Three of the most common uses of satellite imaging are explained below in more detail.

Images and Maps

Satellite image of a city at night

The most well-known example of satellite imaging is probably Google Earth. You can easily use this tool to see your own home. Many other organizations have also developed satellite image databases that are collated into usable maps. This can result in the ability to zoom in to a certain level of detail at any location on the planet.

To create maps, high-resolution images have to be taken at many altitudes for every location. This includes both satellite and aerial photography. Sophisticated software is used to “blend” the altitudes into each other as you zoom in on the map.

Change Detection

Satellites are able to track changes in a given area of the Earth’s surface. A prime example is the polar regions. Satellites are not only able to track how much ice is present at any given time (via visible and infrared light reflection) but are also able to produce topological maps of the ground to measure elevation changes in polar ice.

Weather Prediction

Ever watched the weather forecast or used a weather app? You can thank satellites for that.

Satellites have sensors that are able to capture certain wavelengths of infrared light and can get information about heat levels.

Combined with visible light imaging, satellites can capture a nearly full picture of weather systems. This is because visible light provides information that might not be available via infrared like fog (which is very close to the temperature of the land below it).

Thermal imaging is available at night, too (when visible light isn’t available). This is important for weather prediction because different kinds of weather systems have different heat signatures (for example, cloud types).

Geostationary satellites are able to keep watch over one particular region from a very high altitude. They do this by orbiting the Earth at the same speed that Earth spins. These provide most of the information that you see on the weather forecast. The other kind of weather satellite is polar orbiting and can only image an area twice a day, but provide much higher resolution.

Combining information about heat and reflected light allows for analysis of cloud systems, pollution, fires, storms, surface temperatures, and more.

Satellite Imaging: A New Era of Science

With the advent of satellite imaging, scientists were able to observe the Earth at a new level of detail previously unimaginable. With easy access to worldwide images across the light spectrum, studying weather patterns and ecological patterns became much more sophisticated.

But all new technology comes with a dangerous side as well. Satellite imaging is indispensable for modern militaristic endeavors, including surveilling foreign states or planning strategies.

We hope this article has taught you something you didn’t know about how imaging satellites collect images!