Nonselective scattering

The final scattering mechanism of importance is called nonselective scattering. This occurs when the particles are much larger than the wavelength of the radiation. Water droplets and large dust particles can cause this type of scattering. Nonselective scattering gets its name from the fact that all wavelengths are scattered about equally.
This type of scattering causes fog and clouds to appear white to our eyes because blue, green, and red light are all scattered in approximately equal quantities (blue+green+red light = white light).

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Mie scattering

Mie scattering occurs when the particles are just about the same size as the wavelength of the radiation. Dust, pollen, smoke and water vapour are common causes of Mie scattering which tends to affect longer wavelengths than those affected by Rayleigh scattering. Mie scattering occurs mostly in the lower portions of the atmosphere where larger particles are more abundant, and dominates when cloud conditions are overcast.

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Rayleigh scattering

Rayleigh scattering occurs when particles are very small compared to the wavelength of the radiation. These could be particles such as small specks of dust or nitrogen and oxygen molecules. Rayleigh scattering causes shorter wavelengths of energy to be scattered much more than longer wavelengths. Rayleigh scattering is the dominant scattering mechanism in the upper atmosphere. The fact that the sky appears "blue" during the day is because of this phenomenon. As sunlight passes through the atmosphere, the shorter wavelengths (i.e. blue)
of the visible spectrum are scattered more than the other (longer) visible wavelengths. At sunrise and sunset the light has to travel farther through the atmosphere than at midday and the scattering of the shorter wavelengths is more complete; this leaves a greater proportion of the longer wavelengths to penetrate the atmosphere.

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Scattering

Scattering occurs when particles or large gas molecules present in the atmosphere interact with and cause the electromagnetic radiation to be redirected from its original path. How much scattering takes place depends on several factors including the wavelength of the radiation, the abundance of particles or gases, and the distance the radiation travels through the atmosphere. There are three (3) types of scattering which take place.

• Rayleigh scattering
• Mie scattering
• Nonselective scattering

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Remote Sensing: Visible spectrum

The light which our eyes - our "remote sensors" - can detect is part of the visible spectrum. It is important to recognize how small the visible portion is relative to the rest of the spectrum. There is a lot of radiation around us which is "invisible" to our eyes, but can be detected by other remote sensing instruments and used to our advantage. The visible wavelengths cover a range from approximately 0.4 to 0.7 μm. The longest
visible wavelength is red and the shortest is violet. Common wavelengths of what we perceive as particular colours from the visible portion of the spectrum are listed below. It is important to note that this is the only portion of the spectrum we can associate with the concept of colours.

􀂄 Violet: 0.4 - 0.446 μm
􀂄 Blue: 0.446 - 0.500 μm
􀂄 Green: 0.500 - 0.578 μm
􀂄 Yellow: 0.578 - 0.592 μm
􀂄 Orange: 0.592 - 0.620 μm
􀂄 Red: 0.620 - 0.7 μm

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Remote Sensing

"Remote sensing is the science (and to some extent, art) of acquiring information about the Earth's surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information."



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Cyclones and anticyclones

Cyclones and anticyclones are weather systems that involve masses of air moving in a spiraling motion. In a cyclone, air spirals inward, whereas in anticyclone, air spirals outward. Most types of cyclones and anticyclones are large features that move slowly across the Earth's surface, bringing changes in the weather as they move. These are referred to as traveling cyclones and traveling anticyclones

The circulation of weather systems is determined by their pressure which in turn determines whether air ascends as in the case of low pressure, or descends as in the case of high pressure. Where air rises, condensation and cloud formation results as seen here in the system developing off the west coast of Alaska. In an anticyclone, outspiraling air descends and is warmed adiabatically leading to clear conditions.

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air mass

An Air Mass is a large body of air with fairly uniform temperature and moisture characteristics. Air masses acquire their characteristics from their source regions.

Temperature is indicated using the upper case (for example T for Tropical or P for Polar). Moisture is indicated using the lower case (for example, c for continental (dry) or m for maritime (wet).

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insolation

The word 'insolation' is a contraction of "incoming solar radiation". It consists of a bundle of rays of radiant energy of different wavelengths. The sun emits radiant energy in the form of eletromagnetic waves. The longer waves, largely absorbed in the atmosphere, are called infra-red rays.

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continental shelf

The continental shelf is an undersea extension of a continent which can stretch for many miles out to sea in some cases. In other words a submerged border of a continent that slopes gradually and extends to a point of steeper descent to the ocean bottom.


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