True Colour and False Colours

From Data to Images

From Data to Images

Most Earth observation satellites do not deliver standard colour images. They rather acquire series of greyscale images in different parts of the electromagnetic spectrum. These image bands are used for scientific evaluations, and, similar to the procedures applied in printing and display technology, they are combined to produce colour images of various types for a wealth of different visualisation purposes.

Different from usual photography, the greyscale image bands are combined in various ways. Depending on the application, images are produced in natural colours (true-colour image), false-colour infrared images and other band combinations.

True colours and False-colour infrared Images

While true colour images are used to show the Earth “as it is” (i.e. as it would appear to the human eye) for mapping and illustration purposes, other representations are used to highlight specific properties of the displayed area.

Important additional information is contained especially in the infrared image bands. This information is used e.g. to highlight and to analyse properties of plants, because the chlorophyll contained in the leaves reflects the infrared part of the sunlight very well. This makes this data a valuable information source for applications in agriculture and nature protection.

Other uses for false-colour infrared representations using other infrared bands include analyses of fires and volcanic activities, and of properties of urban spaces.

Exercises

• Satellite Map:
  • Look at the satellite map and zoom in until the satellite image fill the window.
  • Use the slider to compare different features in the false colour infrared visualisation and compare with the true colour image.
  • Check the differences with respect to the brightness of different surface classes. Focus on vegetation classes such as forests and agricultural land
  • Which differences can you identify e.g. with respect to water bodies and to built-up areas?

• Copernicus Browser:
  • Open the Copernicus Browser.
  • Select the different visualisation methods offered by the Copernicus Browser and compare. How is water represented, how agricultural land?
  • Compare specifically the visualisations that use infrared bands, i.e. the False colour, the False colour (urban), and the SWIR (shortwave infrared) visualisations!
  • Search for the most recent Sentinel-2 satellite image covering the region. Is it easy to get cloud-free images? Why/why not?
  • Display the dataset in False colour infrared and compare it with the true colour satellite image. What differences can you detect? What are the reasons for the differences?

Sources and Links