U.U. FACULTY of AGRICULTURE DEPARTMENT of SOIL SCIENCES
REMOTE SENSING & GIS CENTRE

 

WHAT is REMOTE SENSING (RS) ?

 

            Remote sensing is defined as the technique of measuring or gathering information about objects or a phenomenon from a distance without having physical contact with the objects of investigation. It can be briefly regarded as Earth observation or teledetection. The investigation is done by sensing and recording reflected or emitted energy and processing, analyzing and applying that information. The instruments used for this special technology are photographic cameras, mechanical scanners, and imaging radar systems carried on aircrafts and earth observing satellites. The remote sensing platforms are designed to collect and record specific types of energy that impinges upon them. Remote sensing devices differentiated in terms of whether they are active or passive. Active remote sensing systems such as radar and sonar, produced and dispatched energy to a target and record the reflected component. Passive remote sensing systems such as photographic cameras, detect only the energy reflected naturally from an object. It can be sunlight or thermal infrared emission.

 

COMPONENTS of RS

 

             Whether it's sensing from ground, atmosphere or space there are 4 Remote Sensing components in deed;

  • Remote sensing platform

  • Electromagnetic Radiation (Energy source or illumination)

  • Interactions with the Atmosphere

  • Target

ELECTROMAGNETIC SPECTRUM

 

           The electromagnetic (EM) spectrum is the full range of frequencies, from radio waves to gamma rays, that characterizes light. It is the distribution of electromagnetic radiation according to energy. The electromagnetic spectrum covers a wide range of wavelengths and photon energies. Generally, EM radiation is classified by wavelength into electrical energy, radio, microwave, infrared, the visible region we perceive as light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its wavelength. Higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. When EM radiation interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. Hotter, more energetic objects and events create higher energy radiation than cool objects. Only extremely hot objects or particles moving at very high velocities can create high-energy radiation like X-rays and gamma-rays.

            Remote sensing systems which measure energy that is naturally available are called passive sensors. Passive sensors can only be used to detect energy when the naturally occurring energy is available. For all reflected energy, this can only take place during the time when the sun is illuminating the Earth Active sensors, on the other hand, provide their own energy source for illumination. The sensor emits radiation which is directed toward the target to be investigated. The radiation reflected from that target is detected and measured by the sensor. Advantages for active sensors include the ability to obtain measurements anytime, regardless of the time of day or season. Active sensors can be used for examining wavelengths that are not sufficiently provided by the sun, such as microwaves, or to better control the way a target is illuminated.

 
             The zones and wavelength of the  Electromagnetic Spectrum for Remote Sensing are as follows (Ses÷ren 1999).
   1- Optic Wavelength                             : 0.3 - 16 Ám
      A.Reflective Wavelength   
         a.Ultraviolet        : 0.3-0.4 Ám
         b.Visible spectrum  : 0.4-0.7 Ám
                 Blue : 0,4-0,5 Ám
                 Green  : 0,5-0,6 Ám
                 Red  : 0,6-07 Ám
         c.Near infrared : 0.7-0.9 Ám
         d.Moderate infrared      : 0.9-3 Ám
      B.Scatter Wavelength  
                Thermal infrared : 3-15 Ám
   2- Microwaves : 0.83-133 cm
      A.Pasive microwave : 1 mm-1 m
      B.Active microwave (radar)     
        a.SHF (super high frequency)   : 1 cm-10 cm
        b.UHF (ultra high frequency)   : 10 cm-1 m
 
 

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