If an object, feature or phenomenon is located so remotely that it is impossible to come in contact with that object, feature or phenomenon physically, then the method of acquiring information about that particular object by using science is called remote sensing . The required information is transferred through electromagnetic radiation, the ray emitted or reflected from the object which is divided into four wavelengths.
History of remote sensing :
The orgin of remote sensing can be traced back to 19 th century when cameras where used along with kite or balloon to take photographs of the earth surface.. Satellite remote sensing started when both Russia and America took imageries of the surface using sensors from spacecraft. Germany send rockets in 1946 which contained still or movie cameras for capturing images. In 1950, the word remote sensing was first coined by Ms. Evelyn Pruitt of the U.S. Office of Naval Research.
Classification of remote sensing :
• On the basis of sensors used in remote sensing :
• Passive remote sensing : Uses sensors which identifies the electro magnetic radiation reflected or emitted from natural sources.
• Active remote sensing : Uses sensors which identifies the electro magnetic spectrum radiated from artificially generated energy resources for example radar.
• On the basis of wavelength regions identified in remote sensing :
|
Name of the wavelengths |
Wavelengths |
|
Optical wavelength |
0.30-15.0 mm |
| Reflective
• Portion Visible • Near Infrared (IR ) • Middle IR |
0.38-3.00 mm
0.38-0.72 mm 0.72-1.30 mm 1.30-3.00 mm |
|
Far IR ( Thermal, Emissive ) |
7.00-15.0 mm |
|
Microwave |
1mm-1m |
Major components of remote sensing technology:
• Energy source which may be Passive or active
• Platforms for deporting the sensors eg. Aircraft, satellite etc.
• Sensors which detect electromagnetic radiation like camera, scanner
• Detectors for managing signal data for example photographic, digital etc.
• Processing for controlling signal data
• Institutionalization which includes institutes that controls execution of all stages of remote sensing technology.
Resolution of remote sensing :
The resolution is defined as the power of the entire remote sensing technology to give a sharply defined imagery of the earth surface. It can be classified into following types:
• Spectral Resolution is defined by the number of times a particular band is recorded.
• Temporal Resolution is defined as the number of coverages done by the remote sensing system.
• Spatial Resolution is referred to the size of pixel which contains the ground area and is recorded in raster image.
• Radiometric Resolution is the number of different intensities of radiation detected by the sensors.
Satellites of remote sensing :
• TRIOS Series
• NOAA
• GMS
• Landsat
• SPOT
• MOS
• JERS
• ESR
• RADARSAT
• IRS
Spectral Reflectance and Color Readability in remote sensing:
Different features on the earth surface emit or absorb radiance differently depending on the type of object and condition thereby producing different wavelengths. These spectral variation produces visual effect within the visible region of spectrum called COLOUR. Blue objects reflect greatly in the green spectral region. Vegetation appears red, settlement appears grey and river appears blue.
Disadvantage of remote sensing :
• Weather related obstacles
• High cost of data acquisition
• Interpretation problem
Inspite of these disadvantages remote sensing is considered as an important method of data collection and its use is expected to increase in the coming years.
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