Introduction: What is Remote Sensing?

UNDERSTANDING EARTH OBSERVATION - INTRODUCTION

WHAT IS REMOTE SENSING?

Literally, remote sensing means observing an object and gathering information about it without coming into direct contact with it. In fact, we all do this in our daily lives, for example with our eyes and ears. In practice, we use the words ‘remote sensing’ or ‘earth observation’ to indicate that we are collecting and analysing data about the earth's surface using sensors on board any platform in the air or space: satellites, aeroplanes, drones, etc.

These sensors are usually imaging sensors, similar to the digital camera in your smartphone, but just a little more sophisticated. In other words, they take a digital photo of the earth's surface from the air or space.

Unlike an ordinary camera, which can only capture visible light, sensors used for earth observation can also record other parts of the light spectrum. These are mainly infrared and certain microwaves that

• either, like visible light, come from the sun and are reflected;
• or are emitted by the earth (e.g. heat);
• or are emitted by the sensor itself (e.g. radar signal).

This possibility considerably expands the number of observable characteristics and allows us to measure, map and learn much more about the earth's surface than would be possible if we only used ordinary photos. For example, we can distinguish between different agricultural crops, different types of vegetation, different forms of construction, monitor the phenological state of plants, detect landslides, estimate soil moisture and surface temperature, detect illegal dumping, or keep a closer eye on growing cities and shrinking forests.

Remote sensing allows us to observe changes on the earth's surface. Techniques such as LiDAR (Light Detection And Ranging) also enable us to make detailed maps of the topography, for example.

Remote sensing is therefore used in many different domains: meteorology, climatology, glaciology, oceanography, hydrology, land surveying, spatial planning, agriculture, ecology, archaeology, etc., and therefore has a wide range of applications.