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Pixel Thermometer

Many remote sensing sensors can detect thermal radiation emitted by objects upon the Earth's surface via their thermal bands.

In most cases. the spatial resolution of the thermal bands is worse than that of bands of the visible light. This is due to the facts that, in the case of long-wavelength thermal radiation, less energy is emitted per area on the Earth's surface than in the case of short-wavelength radiation. Nevertheless, different surfaces can be distinguished well.

For instance, a city emits more warmth than forests do. Bodies of water, however, have a considerably lower temperature and can be spotted quite easily on thermal images as they stick out as black spots and lines.



Thermal image of Berlin during daytime and nighttime (images processed according to USGS/NASA Landsat Program)



The swipe above shows the city of Berlin during daytime and nighttime in the thermal band of a satellite sensor. Due to the colouring of the image, very cold areas are blue and very warm areas are red.
The Tiergarten (park) and the Spree (river) are clearly visible during daytime as they are cold areas contrasting with their warm surroundings. At night, however, the temperatures have cooled off – the colour scale stayed the same – and adapted to the situation within the city. Now, the Spree, for example, is hardly visible. Only the area surrounding Berlin-Tempelhof Airport sticks out as a cold air basin. In addition, the road network of the German capital is clearly visible. This is due to the fact that asphalt emits warmth much more slowly than, for example, the surrounding houses made of bricks and concrete.





How warm was it Sunday a year ago in Berlin or in Bödefeld (Sauerland)? Satellites constantly record the temperatures of every place on the surface of the earth.