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University of Nebraska–Lincoln

Atmosphere and the Spectrum

The atmosphere is the medium through which electromagnetic energy travels as it journeys from the sun to the earth and eventually to the satellite sensors.

The atmosphere transmits, absorbs and scatters energy. Transmitted energy passes through the atmosphere and reaches the sensor unchanged. Absorbed energy warms the atmosphere or is re-emitted with a changed wavelength.


Atmospheric scattering results when energy's direction is unpredictably changed as it encounters particles in the atmosphere. Scattering of light by particles and molecules results in haze and reduced image sharpness. The effects of scattering are most noticeable in the visible and the infrared wavelengths. There are three types of scattering--Rayleigh, Mie, and non-selective.

Rayleigh Scattering

This is the most common type of scattering. It occurs when the incoming light encounters particles or molecules in the atmosphere whose size is smaller than the photon wavelength. It is responsible for making the sky look blue; the shorter the wavelength, the greater the scattering.(Blue Sky Photo)

Mie Scattering

This occurs when the wavelength of the incoming light is comparable to the size of the particles or molecules encountered. Water vapor, fumes, dust are the main scatters in the earth's atmosphere. This type of scattering is responsible for the red/orange appearance of the sky in the evenings, especially if there has been a forest fire, or a volcanic eruption. Mie scattering is greatly increased when the atmosphere is slightly overcast.(Red Sunset Photo)

Non-selective Scattering

This type affects all visible, near- and mid-infrared wavelengths almost equally. Non-selective scattering occurs when the atmospheric particles causing scattering (such as dust and water droplets) are much larger than the energy wavelengths they encounter. Clouds appear white because equal quantities of blue, green and red light are being scattered.

 

Image Noise

Energy can be scattered into and out of a satellite sensor's field of view. Energy scattered into a sensor's field of view is referred to as "noise." (Sensor Image with noise)

Atmospheric Effects Activities