THE SUN'S LIGHT AND EARTH               [home]   [topic page]

The light that arrives at the outer atmosphere of the Earth is different to that arriving on Earth's surface because of the Earth's air.

The Sun gives off ultraviolet light and X-rays. Fortunately most of these do not reach the surface even on a clear day and despite the "hole in the ozone". The atmosphere is simply not transparent ( clear, like glass ) to these wavelengths. Imagine the cancers that would happen if they were clear to them!

Quite a few infrared frequencies are also eliminated by the air as well.

The above animation shows the light that can get through the air and the wavelengths that Landsat measures - senses.

It is useless for satellites to look for light reflected from surfaces at these wavelengths as the atmosphere absorbs them. This means that satellites only have limited "windows" to observe light coming back up from the ground. The designers of the satellites design sensors for some of these windows - each sensor wavelength group is called a "Band".

Landsat 7 has seven bands while the French SPOT 4 has five bands.