This figure shows that light is not transmitted through the atmosphere equally. Some parts of the spectrum (shown as low values) are absorbed, while others (high values) pass through spectral "windows". The sensors used in satellite instruments are designed to record the parts of the spectrum that pass through the windows. Most of the light recorded is reflected sunlight, but the thermal-infrared (not shown) is radiated by the earth rather than reflected. The thermal infrared is sometimes called the far-infrared. In this illustration it lies far off the right-hand edge of the graph. (Note that 1,000 nanometers (nm) = 1 micrometer (mµ). Source: James B. Campbell, Introduction to Remote Sensing, Taylor and Francis, 2002. The URL of this site is [http://www.geoscience2000.info]