Sunday, April 29, 2007

Thermal Pollution & Remote Sensing

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Thermal water pollution is a potential hazard for aquatic life. Many industries (like thermal power stations) release hot water in their effluent directly to rivers or water bodies. This is also against environmental laws in many countries but detection is difficult because hot water doesn’t have different colour from cold water so our eyes can not recognize it. Secondly such illegal activities mostly practiced in night. So, how to detect it? Answer is- Thermal Remote Sensing.

Thermal pollution can easily detected by thermal remote sensing (or thermal imaging) devices. These operate in thermal infrared bands of EMR and are acquires data to produce night time images. Thermal imaging captures emissions of EMR from an object rather than reflections. When hot water released into a stream it emits thermal radiations which are sensed by thermal imaging devices. Hot water emits more thermal radiations than cold water that’s why it appears brighter & cold water appears darker. Hot water plumes become very clear & conspicuous in thermal images, we can detect the source of release and the extent of spread of hot water.

Urban Heat Detection

Urban areas behave as heat islands due to very high emission of thermal radiations. Their temperature remain higher than surrounding non-urban areas- basically due to high energy consumption, very large surface area covered by asphalt and concrete, lesser soil surfaces and low vegetation cover.

Energy is mostly consumed in the form of electricity and in the process large amount of heat is released. While concrete and asphalt surfaces (like buildings, roads, pavements etc.) absorb solar radiations and later release thermal emissions. Vehicular and industrial pollution in cities also contribute to heat emissions and so in increasing urban ambient temperature.

Thermal imaging devices help in detecting relative warmness/coolness of urban islands. High energy consumption areas and hot spots can be mapped using thermal remote sensing images. As we all know vegetation reduces ambient temperature significantly so thermal imaging can help in identifying urban areas where plantation is required to cool down the hot spots.

3 comments:

tarek said...

Hi... Thank you very much for these useful information. Do you have any idea concerning the resolution of civil satellite thermal imaging devices ?
Again thanks for this article.

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