PRINCIPLE OF REMOTE SENSING

PRINCIPLE OF REMOTE SENSING

A) ELECTROMAGNETIC RADIATION

Ø The Energy is either come from the natural source sun or from various artificial sources. It is known as electromagnetic Radiation as this energy consists not only an Electrical field but also a magnetic field.

a)    Electrical Field (E): This field is generated perpendicular to the direction of radiation traveling.

b)    Magnetic Field (M): It is exactly oriented at right angles toward the electrical field.

Ø Electromagnetic energy can be described in terms of its velocity, frequency and wavelength.

Ø Energy waves travel similar to the speed of light, c, which is approximately equal to 3×10^8 m/s.

Ø Wavelength λ of the wave is the distance from any point on one wave to a similar position on the next wave which means between two successive peaks.

Ø The wavelengths most of used in remote sensing are very short. It is normally expressed in micrometers (μm). 1 μm is equal to 1×10-6 m.

Ø  Frequency f is the no of waves passing a fixed point per unit of time. It is generally expressed in Hertz (Hz). This implies that wavelength (λ) and frequency (Hz) are inversely related where c is a constant. The important fact is that always longer wavelengths have smaller frequencies compared to shorter wavelengths.

Ø The Electromagnetic energy interacts with the earth’s surface and various features like bared soil, buildings, grass, vegetation, water bodies, and forests etc.

Ø The Response from the ground earth's surface to incoming energy is the reflection, and the all energy emitted by all objects as a function of temperature & structure is the emittance.

B)  ELEMENTS OF REMOTE SENSING

1)    Source of Illumination/ Energy: The important requirement for any remote sensing process is to have an energy of source which illuminates and provides electromagnetic radiation to the target of interest on the earth surface.

2)    Radiation and the Atmosphere: Energy is reached at any point in the atmosphere as it passes through. This type of interaction may take place 2^nd time as the whole energy travels from the target on the ground and again back to the sensor. Atmosphere modifies the wavelength & Spectral distribution of energy to some extent level.

3)    Interaction of Energy with the Target: Once the energy in the form of radiation makes its path to the target level through the atmosphere, it strikes the target depending on the characteristics and features of both the target (object) & the radiation. Whenever energy received by the object interacts here it is either transmission, absorption, scattering, emitted or reflected from the target.

4) Recording of Energy by Sensor: Moving further the energy has been scattered or emitted from the target, the sensor is required to collect, receive and record the electromagnetic radiation (EMR). Return Signal is adjusted to a sensor that actually responds to various types of wavelengths.  

5) Transmission, Reception, and Processing: The energy which was recorded by the active or passive sensor has to be transmitted, often in the form of electronic, to a receiving and processing ground station where the actual data are processed into a satellite image could be available in the hardcopy as well as in the digital format.

6) Interpretation and Analysis: The processed satellite image is interpreted visually, digitally, or else electronically, to extract all kinds of information and data regarding the target or earth object which was illuminated.

7)  Users and application: The final purpose of remote sensing technology is achieved when the useful important information is extracted in the desired form. Afterward, any scientist or assistant could resolve a particular problem.