How does remote sensing work? Reading a changing planet from space

Remote sensing is how scientists study a place without touching it, using satellites and aircraft to turn light into data. Here’s how it works, from wildfires to forests to reefs, shown through one of its boldest uses: mapping every shallow coral reef on the planet.

It’s not reasonable to swim every reef in the ocean to track data. There are too many, change too fast and are spread across waters too vast. So how do scientists know where the world’s coral reefs are and if they are healthy? They look from far away, with an approach called remote sensing.

Remote sensing allows scientists to read forests, farmland, rivers and cities, too. Reefs are just one of the clearest places to watch it work. Once you understand it, you start seeing the planet the way a scientist does.

It’s also a skill you can learn. The scientist whose work you’ll follow in this article, Assistant Professor Jiwei Li, teaches Earth Intelligence, one of ASU’s Universal Learner Courses, which anyone can start with no application. First, the concept.

What is remote sensing?

Remote sensing means gathering information about a place from a distance, usually with sensors on satellites or aircraft. Instead of standing in a forest or diving to a reef, you capture the light and energy bouncing off Earth’s surface and read what it tells you.

The idea is simple. Everything reflects light in its own way. Healthy plants, dry soil, open water and a coral reef each send back a different pattern of light. Scientists call that pattern a spectral signature. Learn to read the signatures, and a satellite image becomes a map of what is actually on the ground or under the water.

How a satellite sees a coral reef

Coral reefs sit in shallow, clear water, which makes them possible to map from orbit. Sunlight passes through the water, reflects off the sea floor and travels back up to the satellite. The light that returns from living coral looks different from the light that returns from sand or seagrass.

A satellite also helps measure how deep the water is. Because light fades in a predictable way as it moves through water, scientists can work backward from the image to estimate depth. Put depth and surface reflection together, and you can tell coral from rubble, and reef from open sea.

How AI turns images into a map

A single satellite image is millions of pixels. Sorting each one by hand would take lifetimes. This is where machine learning comes in.

Scientists train a computer model on examples: this signature is coral, this one is sand, this one is deep water. The model learns the patterns, then classifies every pixel across enormous stretches of ocean in a fraction of the time. The result is a habitat map that covers areas no dive team could ever reach.

The same idea reads the whole planet

Reefs are one example. The same approach works everywhere. Using satellite data, scientists can detect the heat of a wildfire before a forest or park crew can see the flames. The scientists watch a forest thin from logging, season by season. They track a reservoir dropping through a drought and map which city blocks trap the most heat in summer. Different questions, same process: measure the light and energy a place gives off, then interpret what those signals mean about the world below. Applying those skills across forests, cites, landscapes, and oceans is the foundation of Earth Intelligence. Reefs are just one of the easiest places to see it in action.

The scientist behind the map

This is the daily work of Jiwei Li, assistant professor in the School of Ocean Futures at Arizona State University and a remote sensing scientist, biological oceanographer and computer scientist. Li runs the Remote Sensing for Global Futures Lab, where the tools above are used to study oceans, rivers and lakes.

Li was first author on the first AI-driven map of the world’s shallow coral reefs, part of the Allen Coral Atlas. The team combined satellite imagery, water-depth calculations and machine learning to map coral habitats at a scale never done before, from a single reef to entire barrier systems across more than 6 million square kilometers of ocean.

Li called the result ASU’s “best estimate of the location of shallow coral reefs on the planet.”

Scientists now use it to decide where to watch for coral bleaching.

The work continues. In 2025, Li co-authored a study charting a path to restore Hawaiʻi’s reefs through the ʻĀkoʻakoʻa program, using the same skills to find where restoration can take hold.

Learn to do this yourself

Most people don’t realize these are learnable skills, and you can start with a single course. Li teaches Earth Intelligence: Data, AI and a Changing World, an 8-week online ASU course that teaches the same tools and techniques featured in this article and applies it across environmental systems, from local to global. You work with satellite imagery, use Google Earth Engine to explore environmental data and learn how AI reads patterns across a landscape. You also cover the ethics of handling that data, which matters as much as the analysis.

You can start now

Earth Intelligence is one of ASU’s Universal Learner Courses, and there’s no risk in trying it. Anyone can enroll for $25 with no application and work at their own pace over 8 weeks. You see your grade, and pay the $400 only if you like it and want the credit on your ASU transcript. That credit is highly transferable and can ladder toward a degree at ASU. High school students can see about dual credit with their counselor via Accelerate ASU, and adults can earn admission to ASU and build toward a degree through ASU Earned Admission.

You don’t need a lab or a satellite to begin. You need curiosity and one course.

Ready to read the planet the way a scientist does? Explore Earth Intelligence and enroll.