Remote sensing
Data acquisition
  The electromagnetical spectrum
  Digital images
  The sensors
  In remote sensing
  Getting into orbit
  Remote sensing images
  Additional data
Image processing

Standing up to the radiometer’s intense gaze

The spectro-radiometer is used to analyse all the details of an electromagnetic spectrum. This instrument can analyse all of the frequencies of the spectrum. Other instruments measure the intensity of radiation in just a few frequency ‘windows’.

These instruments normally work by means of a sensitive element or detector that modulates the current passing through it in line with the electromagnetic energy that it receives. Different types of detector are used for the different wavelengths. Each machine is usually equipped with a single detector and thus takes readings on a certain wavelength interval. The result is a graph of the type shown before.

Several sensitive elements can be placed side by side to create a matrix of sensors. Each individual sensor acts like a spectro-radiometer, but if the (numerical) readings of each sensor are considered to be so many numerical values associate with a pixel in an image, the result is an imaging spectro-radiometer. For example, a spectro-radiometer composed of cells that are sensitive to thermal infrared waves will record higher values in hotter areas. If the pixel coding convention is ‘0 = black, 255 = white’, these hot spots will correspond to the palest areas in the image.