1. Definition of Remote Sensing (RS)
Remote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object (Wikipedia). Remote sensing is a generic term which describes the action of obtaining information about an object with a sensor which is physically separated from the object. It primarily concerned with deriving information about the earth’s surface using an elevated platform (Harrison and Jupp, 1989).
2. Brief history of RS
Brief history of RS is adapted from Reeves et al. (1975) and Verstappen (1977).
- In 1783, first balooning by Marquis d’ Arlandes and Pilatre d’ Rosier in Paris.
- First photographs taken in 1839, next year, in 1840, first topographic maps were prepared.
- In 1858, Parisian photographer and baloonist G.F. Tornachon (known as Nadar) made the first aerial photographs. Same year, Laussedat developed a mathematical analysis for converting overlapping perspective views into orthographic projections on any plane.
- In 1860 and 1886, first aerial photographs were taken in Boston (USA) and Russia
respectively from a free baloon.
- First photo interpretation during 1967-68-69 in USA for geological survey.
- In 1882 and 1895, kites were used in England and Western hemisphere to take photos.
- In 1903, carrier Pigeons were used to take photos by J. Neubronner at 30 second intervals.
- At the end of nineteenth century, Rockets were first used to take photos by the Germans.
- At the beginning of twentieth century, improved aircraft, camera system and photographic illusions have gradually resulted in ever improved RS technology.
- In 1946, hyper altitude photos taken by earth observatory satellites.
- In 1960, the term remote sensing was coined in lieu of aerial photography.
3. RS system
A system denotes the total appearance of all components, their interactions in doing a particular job. Remote sensing system comprises all the available components (both hard and soft wares), the online server, their interactions and interrelations in doing a particular job like image processing from satellite data. RSS comprises following components:
Platforms: The Satellite carrying the remote sensing device.
Sensor: The remote sensing device recording wavelengths of energy.
Computer system: The total computer hardware and software system.
Server: The server of the software development company that links with server stations.
Institutional setups: Cartography, image processing, other infrastructures etc.
Energy source: There must be an energy source for viewing the surface feature may be the Sun.
Image interpretation: The system of image interpretation is done by analyzing the captured image.
4. Interactions of EME with earth surface
Electro-magnetic energy (EME) interactions with atmosphere and with the earth surface play a vital role in remote sensing. Energy interactions with the atmosphere dictate the spectral regions through which only we can do the remote sensing which are known as Spectral windows (the spectral regions where atmosphere is more or less transparent).
The total incident energy will interact with earth’s surface materials in three ways. These are: Absorption, Transmission, and Reflection. Absorption (A) occurs when radiation (energy) is absorbed into the target while transmission (T) occurs when radiation passes through a target. Reflection (R) occurs when radiation "bounces" off the target and is redirected.