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Remote Sensing |
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It was after the advent and end of World War Two, that remote sensing came of age. Aerial photography of enemy positions from airplanes was very helpful to both, especially to the Allied forces. Remote sensing can be defined as the collection of data about an object from some distance. Geographers use the technique of remote sensing to monitor or measure phenomena found in the Earth's lithosphere, biosphere, hydrosphere, and atmosphere. Remote sensing of the environment by geographers is usually done with the help of mechanical devices known as remote sensors. These sensors are usually positioned away from the object of interest by using helicopters, planes, and satellites.
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Most sensing devices record information about an object by measuring an object's transmission of electromagnetic energy from reflecting and radiating surfaces.
Remote sensing imagery has many applications in mapping land-use and green cover, agriculture, forestry, soils mapping,city planning, military observation, archaeological investigations and geomorphological surveying. Remote sensing applications and Remote sensing Canada are related subjects. Remote Sensing is the science and art of gathering spectral, spatial, temporal information about material objects, area or phenomenon. It is a non-contact investigation. Without direct contact, some means of transferring information through space must be utilized. In remote sensing, information transfer is accomplished by use of electromagnetic radiation (EMR). Electo magnetic radiation, EMR, is a form of energy that reveals its presence by the observable effects it produces when it strikes the matter. EMR is considered to span the spectrum of wavelengths from 10-10 mm to cosmic rays up to 1010 mm, the broadcast wavelengths, which extend from 0.30-15 mm.
There are many good ways of classifying remote sensing radiation resources. These are:
One is by types of resources:
Passive Remote Sensing: Makes use of sensors that detect the reflected or emitted electro-magnetic radiation from natural sources.
Active remote Sensing: Makes use of sensors that detect reflected responses from objects irradiated by artificially-generated energy sources, such as radar.
Another way is by classifying wavelength regions such as Visible and Reflective Infrared Remote Sensing, Thermal Infrared Remote Sensing and Microwave Remote Sensing.
Thermal infrared radiation refers to electromagnetic waves with a wavelength of between 3.5 and 20 micrometers. Most remote sensing applications make use of the 8 to 13 micrometer range. The major difference between thermal infrared and the infrared (color infrared - CIR) discussed is that thermal infrared is emitted energy that is sensed digitally, whereas the near infrared "photographic infrared" is reflected energy that causes a chemical reaction in film emulsion. Thermal Infrared ranges from 5.6 um to 1cm. Water and other gases in the atmosphere restricts aerial systems to two wavelength windows; 3 to 5 um and 8 to 15 um (absorption bands). Thermal IR imagery is difficult to interpret and process because there is absorption by atmospheric moisture.
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