Wednesday, 21 November 2018

The Visible Portion Of Electromagnetic Spectrum!!!

Know And See Which Is The Visible Portion Of Electromagnetic Spectrum And How Many Different Portion In The Electromagnetic Spectrum!!! 

The visible spectrum is the portion of The Electromagnetic Spectrum that is visible to the human eye.

Electromagnetic radiation in this range of wavelengths is called visible light or Simply Light. A typical Human Eye will respond to wavelengths from about 380 to 700 nanometers.

In terms of Frequency, this corresponds to a band in the vicinity of 430–770 THz.

The Electromagnetic Spectrum

The Electromagnetic Spectrum ranges from the shorter wavelengths (including gamma and x-rays) to the longer wavelengths (including microwaves and broadcast radio waves).

There are several regions of The Electromagnetic Spectrum which are useful for remote sensing.

Ultraviolet Portion

For most purposes, the ultraviolet or UV portion of the spectrum has the shortest wavelengths which are practical for remote sensing.

This radiation is just beyond the violet portion of The Visible Wavelengths, hence its name.

Some Earth surface materials, primarily rocks and minerals, fluoresce or emit visible light when illuminated by UV radiation.

Ultraviolet (UV) light has wavelengths of 10 – 310 nm. The Sun is a source of ultraviolet Energy.

The UV portion of the spectrum is subdivided into UV-A, UV-B, and UV-C.

UV-C rays are the most harmful and are almost completely absorbed by our atmosphere.

UV-B rays are the harmful rays that cause sunburn. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them.

The Visible Spectrum

The Light which our eyes - our "remote sensors" - can detect is part of the visible spectrum.

It is important to recognize how small the visible portion is relative to the rest of the spectrum.

There is a lot of radiation around us which is "invisible" to our eyes, but can be detected by other remote sensing instruments and used to our advantage.

The visible wavelengths cover a range from approximately 0.4 to 0.7 mm.

The longest visible wavelength is red and the shortest is violet.

Common wavelengths of what we perceive as particular colours from the visible portion of the spectrum are listed below.

It is important to note that this is the only portion of the spectrum we can associate with the concept of colours.

  • Violet: 0.4 - 0.446 mm
  • Blue: 0.446 - 0.500 mm
  • Green: 0.500 - 0.578 mm
  • Yellow: 0.578 - 0.592 mm
  • Orange: 0.592 - 0.620 mm
  • Red: 0.620 - 0.7 mm

Blue,  green, and red are the primary colours or wavelengths of the visible spectrum.

They are defined as such because no single primary colour can be created from the other two, but all other colours can be formed by combining blue, green, and red in various proportions.

Although we see sunlight as a uniform or homogeneous colour, it is actually composed of various wavelengths of radiation in primarily the ultraviolet, visible and infrared portions of the spectrum.

The visible portion of this radiation can be shown in its component colours when sunlight is passed through a prism, which bends the light in differing amounts according to wavelength.

  • Visible light covers the range of wavelengths from 400 – 700 nm. This is the only region in spectrum that human eyes are sensitive to. 
  • The Sun emits the most radiation in the visible portion of the spectrum. Each individual wavelength within the spectrum of visible light wavelengths is representative of a particular color.
  •  Light at the lower end of the visible spectrum, having a longer wavelength, about 740 nm, is seen as red; 
  • light in the middle of the spectrum is seen as green; and light at the upper end of the spectrum, with a wavelength of about 380 nm, is seen as violet.
  •  When all the wavelengths of the visible light spectrum strike your eye at the same time, white is perceived. 
  • The visible portion of the spectrum is used extensively in remote sensing and is the energy that is recorded using photography.


The next portion of the spectrum of interest is the infrared (IR) region which covers the wavelength range from approximately 0.7 mm to 100 mm - more than 100 times as wide as the visible portion! The Infrared Region can be divided into two categories based on their radiation properties - the reflected IR, and the emitted or thermal IR.

Radiation in the reflected IR region is used for remote sensing purposes in ways very similar to radiation in the visible portion.

The reflected IR covers wavelengths from approximately 0.7 mm to 3.0 mm.

The thermal IR region is quite different than the visible and reflected IR portions, as this energy is essentially the radiation that is emitted from the Earth's surface in the form of heat.

The thermal IR covers wavelengths from approximately 3.0 mm to 100 mm.

  • The infrared portion of the spectrum ranges from approximately 0.7 µm to 100 µm in wavelength.
  •  It is divided up into three main regions, Near Infrared (NIR) 0.7 – 1.3µm, Shortwave Infrared (SWIR) from 1.3 – 3 µm and the Far or Thermal Infrared 3 - 100 µm.
  •  Infrared radiation is used extensively in remote sensing. 
  • Objects reflect, transmit, and absorb the Sun's near-infrared and shortwave radiation in unique ways and this can used to observe the health of vegetation, soil composition and moisture content. 
  • The region from 8 to 15 µm is referred to as thermal infrared since these wavelengths are best for studying the longwave thermal energy radiating from the Earth.


The portion of The Spectrum of more recent interest to remote sensing is the microwave region from about 1 mm to 1 m.

This covers the longest wavelengths used for remote sensing.

The shorter wavelengths have properties similar to the thermal infrared region while the longer wavelengths approach the wavelengths used for radio broadcasts.

  • Microwaves are essentially high frequency radio waves and have wavelengths that range 1mm to 1m.
  •  Different Wavelengths or bands of microwaves are used for different applications.
  •  Mid-wavelength microwaves can penetrate haze, light rain and snow, clouds, and smoke are beneficial for satellite communication and studying the Earth from space. 
  • Radar Technology sends pulses of microwave energy and senses the energy reflected back.

Gamma Rays

Gamma rays have the shortest wavelengths (< 0.01 nanometers ) and the most energy of any region of The Electromagnetic Spectrum. Gamma rays are produces by the hottest objects in the universe, including neutron stars, pulsars, supernova explosions.

Gamma rays can also be created by nuclear explosions. the majority of gamma rays generated in space are blocked by the Earth's atmosphere.

This is a good thing as gamma rays are biologically hazardous.


X-Rays range in wavelength from 0.01 – 10 nm and are primarily generated from by super-heated gas from exploding stars and quasars. X-rays are able to pass through many different types of materials.

X-rays are commonly used for medical imaging and for inspecting cargo and luggage. Similar to gamma rays, the Earth's atmosphere blocks x-ray radiation.

Radio Waves

Radio waves have the longest wavelengths in The Electromagnetic Spectrum with wavelengths ranging from approximately 1mm to several hundred meters.

Radio waves are used to transmit a variety of data. Wireless networking, television and amateur radio all use radio waves.

The use of radio frequencies are usually regulated by governments.