b.) ( Explain electromagnetic spectrum - 3 marks, Parts of em spectrum- 7 Marks)
Electromagnetic Spectrum

Electromagnetic spectrum (EMS) represents the continuum of electromagnetic radiation (EMR)
arranged on the basis of wavelengths or frequency.

Electromagnetic spectrum ranges from shorter wavelengths (gamma rays to x rays) to the longer

wavelengths (microwave and radio waves).

Most common remote sensing systems operate in one or several of the visible, infrared and
microwave portions of the electromagnetic spectrum. Within the infrared portion of the
spectrum it should be noted that only thermal infrared energy is directly related to the sensation

of heat; not the near and mid infrared ones.

Different radiations which constitute the EMS are as follows:

Radio waves
These are the longest wavelength (lowest frequency) radiations of the EMS. The wavelength of
radio waves is more than 100 cm. These passes through Earth's atmosphere easily. Radio signals

are used in radios, televisions, aircrafts, ship etc. These are also emitted by stars.

Microwaves
Their wavelength ranges between Imm & Im. RADAR (Radio Detection And Ranging) is the
most common device used in Microwave Remote Sensing. Other applications are in cooking

food (microwave oven), in broadcasting transmissions etc.

Infrared Radiations

When we feel hot it is because of infrared (IR) radiations. For common understanding we can
call them as 'Heat'. The wavelength of IR is longer than visible light and shorter than microwaves
approximately ranges between I micron to 100 microns. These are very useful radiations for
remote sensing. Thermal Imaging Systems detect objects by recording their temperature (infrared

emissions).

Visible Radiations