At mundialis, we use earth observation data collected by sensors on satellites orbiting the earth. These sensors can be thought of as special cameras that can detect a large number of frequencies in the electromagnetic (EM) spectrum emitted by the Sun. Thanks to our atmosphere, we only see certain parts of the electromagnetic spectrum. The graph below shows our “atmospheric window”. The EM energy (in blue) is what we can see on Earth: Our eyes can only see the visible part – red, green and blue. Healthy vegetation (or chlorophyll) reflects more green light compared to other wavelengths. It absorbs more red and blue light. This is why our eyes see it as green. Other objects, such as bare ground, cities or roads, rivers and lakes, also have their own specific reflective properties that make them look the way they do. But special types of sensors can pick up other forms of the EM spectrum – invisible to the human eye. For example, vegetation reflects even more in the near infrared (NIR). NIR is invisible to the human eye, but sensors can pick up this spectral band. This means that special types of sensors can reveal new information about the Earth’s features that our eyes can’t. Depending on what the scientist wants to study, different spectral bands need to be combined, resulting in different colours of the same objects, as described above.