Spectral Resolution

Spectral resolution is defined through the number of spectral bands and their width. Their purpose is to capture the differences in the reflection characteristics from different surfaces.

While the human eye only recognizes the visible spectrum of light, a satellite can, depending on the type, depict the light differently in many spectral areas. The majority of passive earth observation satellites have between 3-8 bands and are therefore called multispectral as for example the American LANDSAT-Satellite and the French SPOT (see image).

The higher the spectral resolution, the narrower is the wave length for a specific band, and therefore, the more bands there are. With a higher spectral resolution single objects can be perceived better and spectrally distinguished.

Visible light: In the area of visible light passive satellite sensors are as sensitive as the human eye. Satellites "see" about the same as a person would see when looking at the earthfrom an altitude of about 1,000 km. The satellites, however, only capture what is being lit by the sun.

Infrared sensors measure different dregrees of heat in near, middle, and far (thermal) infrared, which will then be converted into individual spectral colours. They measure, for example the surface temperature of clouds and can therefore contribute information about the dimensions of clouds (as used for El-Niño forecasts).

Panchromatic data generally designates the spectral sensitivity of a sensor. The reflection values will then be given in a differentiated grey scale (in black and white) (Albertz 2007, Lillesand, Kiefer 2004).