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Chapter 1
What Is Remote Sensing?
Welcome to the start of your journey to remote sensing mastery! Over the next 12 chapters, we’re going to take you up into space and introduce you to the world of satellite data, showing you what your eyes can see and unveiling things your eyes can’t.

There are hundreds of satellites orbiting the Earth and you use their data every day, whether it’s to make mobile telephone calls, for car navigation, or watching the news and weather. We’re passionate about the satellites that collect environmental data, which can help explore, explain, and monitor what is happening here on Earth. The data from these satellites are used to monitor the health of the oceans, provide lifesaving support in earthquakes, monitor climate change, or provide early warning systems for floods. All of these applications, and many more, are provided through remote sensing data.

What’s more, most of these data are freely available and can be used by anyone with a reasonable computer and Internet connection. This book is going to take you through the theory, with supported practical exercises, to show you how to find, download, manipulate, and view these amazing data sets. You can investigate your local area, or anywhere in the world, and improve your understanding of the environment, or perhaps even develop new applications no one has developed yet. Remote sensing is a young, growing space-based industry waiting to be discovered.

This first chapter will provide you with an overview of remote sensing, by explaining what it is, its history, how it works, and why it’s useful. The final section describes the structure of the book and what will be covered within the individual chapters.

We hope that the book will interest, intrigue, and inspire you to get involved with remote sensing data and begin to use it to explore our planet. Get ready to take your first step.

1.1 Definition of Remote Sensing
The simplest definition of remote sensing is being able to know what an object is without being in physical contact with it (inspired by Sabins 1978). You do that every day with your eyes, as you don’t have to touch a table or a chair to know what it is. Now imagine your eyes were up in space and could see the whole world; could you tell what type of tree was in a forest by looking at it, or how warm the ocean was, or whether the level in the river is rising, or whether air quality over a particular town is good or bad? Well, this is exactly what satellite remote sensing can do.

Remote sensing is essentially the collection of data by sensors on either aircraft or satellites, although there are other approaches e.g., in the Amazon, there are a number of tall vertical platforms topped with sensors that are then processed by computer systems to provide information and images about a particular area.

Because remote sensing generally monitors the planet, the term Earth observation (EO) has recently become popular, to describe what remote sensing does. However, there is also the remote sensing of other planets, and their moons, in the solar system, and even remote sensing of comets, which, in 2014, was a key part of the European Space Agency Rosetta mission to land on Comet 69P Churyumov-Gerasimenko.

Remote sensing essentially gives us an opportunity to better understand what is happening on our planet.

Using Earth Observation to answer questions about our planet’s resources and behaviour