3. Resolution

Display of remote sensing data

Satellite images are not photographs but pictorial presentations of measured data. Satellite systems measure electromagnetic radiation in different "areas" or bands of the electromagnetic spectrum (e.g. in the visible or infrared range).

Which "Areas" or Bands Are Detected?↓ ↑

Six out of eight bands of the LANDSAT 7 satellite (in grey) and three spectral reflection curves
Own illustration, Source: Siegmund, Menz 2005.

Separating the whole electromagnetic spectrum in different spectral bands has the advantage of combining these bands in various ways and therefore gain more information compared to solely panchromatic images (with only one band).

In each band, grey scales are assigned respectively to the intensity of the electromagnetic radiation and saved digitally in pixels. Through assigning the three fundamental colours (red, green and blue) to three different bands satellite image composites are produced.

As an example, the US satellite LANDSAT 7 possesses 8 bands. With a band combination of 3, 2, 1 an apparently natural image or true colour satellite image is produced.

Source: satimagingcorp.com.

The Landsat Program is a series of earth-observing satellite missions jointly managed by NASA and the U.S. Geological Survey. Since 1972, Landsat satellites have collected information about earth from space.
The government-owned Landsat 7 was successfully launched on April 15, 1999. The earth observing instrument on Landsat 7, the Enhanced Thematic Mapper Plus (ETM+), replicates the capabilities of the highly successful Thematic Mapper instruments on Landsats 4 and 5.

Official web page:http://landsat.gsfc.nasa.gov/

True colour satellite image of the region of Karlsruhe, Germany, acquired with LANDSAT in 1999.
Source: Landsat

More features or earth surface structures can be detected through other bands or band combinations. These include water bodies, different vegetation species or land use classes. Earth surface temperatures can be detected with thermal bands as well.

These other band combinations are so called false colour images. They show land cover types in "false" colour compared to what we see with our eyes (see LANDSAT false colour image examples in the switch-box below).

False - 543 False - 215 False - 342 False - 341

False colour satellite image of LANDSAT 7 of the Rhein-Neckar region, Germany (band combination 543).
Source: Landsat

Other than assigning the three fundamental colours to different bands, mathematical operations applied to the raw data can provide more information. Artificial bands can be derivated, e.g. vegetation indices showing the plant vitality expressed through NDVI (Normalized Difference Vegetation Index).