REMOTE SENSING AND WAVE LENGTH

REMOTE SENSING

Remote sensing is a process of obtaining information about an object, area, or phenomenon through the analysis of data by a device without being in contact with the object, area or phenomenon being studied. It is a methodology employed to study from a distance the physical and chemical characteristics of objects. Human sight, smell, and hearing are examples of rudimentary forms of remote sensing. Photographic interpretation is considered a form of remote sensing, however, it is generally limited to a study of images recorded on photographic emulsions sensitive to energy in or near the visible portion of the electromagnetic spectrum. Remote sensing discuss in this chapter treats sensor system which record energy in more quantifiable formats over a much broader range of the electromagnetic spectrum. Most of the remote sensing methods make use of the reflected infrared band, thermal infrared band, and microwave portions of the electromagnetic spectrum.

NECESSITY AND IMPORTANCE

With growing population and rising standard of living, pressure on natural resources has been increasing day by day. It, therefore, becomes necessary to manage the available resources effectively and economically, it requires periodic preparation of accurate inventories of natural resources both renewable and non-renewable. This can be achieved through remote sensing very efficiently since it provides multispectral-multitemporal data useful for resources inventory, monitoring and their management.

APPLICATIONS AND SCOPE

Remote sensing is being used to collect the information about agriculture, forestry, geograph, archeology, weather and climate, marine environment, hydrology, water resources management and assessment, engineering, etc. It has vast applications in exploration of natural resources, analysis of land use and land cover, information about environments, natural hazard studies such as earthquakes, land slide, land subsidence, flood, etc.

ELECTROMAGNETIC ENERGY AND ELECTROMAGNETIC SPECTRUM

Electromagnetic energy is a form of energy which moves with velocity of light in a harmonic pattern consisting of sinusoidal waves of varying wavelength. Remote sensing makes use of electromagnetic radiation which is not visible to human eyes.

            Electromagnetic energy is detected only when it interacts with matter. For example, light is seen in dark only when electromagnetic radiation interacts with dust and other particles present in air.

            The change in electromagnetic energy takes place when it interacts with the earth’s surface and environment. Remote sensing detects these changes and the data obtained is used for determination of the characteristics of the earth’s surface.

Electromagnetic waves can be described In terms of three basic parameters:

1.      Velocity (c)

2.      Wavelengths (λ)

3.      Frequency (ϝ)

The following relationship exists between the above three parameters:

                        Λϝ = c i.e., = 3.8 * 10⁸ m/sec.

Where  λ is in meters  and ϝ is in hertz.

Electromagnetic spectrum ranges from most energetic rays at wavelength less than 10^-13m to very long waves at wavelength longer than 100km. various components of an electromagnetic spectrum with their wavelengths are given below:

            1.  y and X rays                               Up to 10^-8m wavelength region.

            2. Ultraviolet                                  from 10^-9 to 10^-7m.

            3. Visible region                             (0.4 – 0.7) Um is only one of many forms                           

                                                            electromagnetic energy and mostly used to acquire remotely sensed data for natural resources mapping. This wavelength interval is generally referred to a LIGHT.

            4. Near-, Middle-, Thermal                from 0.7 to 20Um: Near Infrared- (0.7- 1.3) um,

                        Far – Infrared.                          Middle Infrared- (1.3 – 3.0), Thermal Infrared- (3.0 –

                                                                              14.0) um, and Far Infrared- (7.0 – 15.0) um.

            5. Microwave region                            Down to a wavelength of 1m.

            6. Radio waves.                                     Wavelengths longer than 1m.

There are certain regions of electromagnetic spectrum which can penetrate through the atmosphere without any significant loss of radiations. Such regions are called atmospheric windows.

            Electromagnetic radiations are affected by atmospheric effects known as scattering and absorption.