1. ELECTROMAGNETIC SPECTRUM – THE WAVES
AROUND US
Prachi Sukumar Mehta
Code # MG0712
CEPT University
Faculty of Geomatics and Space Applications
2. ELECTROMAGNETIC SPECTRUM
• The colors of rainbow form only the visible part of the spectrum. All other rays
are invisible to human eye.
• The electromagnetic waves have different wavelengths and carry different
amount of energy.
• Longer wavelengths have less energy while shorter wavelength have more
energy.
• Why Important? – The waves interact with matter in a specific way, each band
of wavelengths behaves in a unique way.
• Remote sensing is a very narrow and specialized application of the properties of
these waves. There are many more.
4. INFRARED RAYS
• Similar to microwave. They heat things. Heat rays from fire, radiator or the Sun
are in fact infrared rays.
• Infrared images are called Thermographs. They are useful as amount of carbon
dioxide in atmosphere, ocean currents, coral reefs and diseased crop can be
mapped using this type of imagery.
• These cameras can ‘see’ in the dark. All warm objects emit infrared rays.
5. INFRARED IMAGING
Clockwise from top-left : Coral reef in Florida, Carbon Dioxide in Troposphere , Cup of
coffee, Fault in industrial fuse block
6. X-RAYS
• They are able to penetrate soft materials like flesh but not hard substances.
• Often used in medicine.
• Larger doses can destroy living cells of body.
• Traditionally Angioplasty is carried out by injecting a radio-opaque contrast agent into blood
vessel and imaging using X-Ray based techniques.
8. GAMMA RAYS
• Similar to X-Rays but even more penetrating power
• Present in radiation from nuclear reactors
• Need heavy shielding for protecting people around. Can be shielded using
materials of high atomic number and high density.
• Small doses of Gamma rays and X-Rays are useful in destroying cancerous
tissue.
9. ULTRAVIOLET RAYS
• Tans the skin, produces vitamin D
• Many insects are attracted to UV light and therefore UV traps are used to kill
them by electric shock. UV light is used to disinfecting water as well as
laboratories and medical facilities.
• Some substances glow like luminous paints when kept under ultraviolet light.
• Such materials are used to print post codes on envelopes so UV detectors can
automatically sort the letters.
• UV watermarks protect sensitive documents like passport, credit cards.
11. IMAGERY OF THE SUN USING ULTRAVIOLET RAYS
False color Ultraviolet Image
12. RADIO WAVES
• Used to broadcast radio and television. For instance, AM/FM radio.
• Long wavelengths ranging from a few centimeters to hundreds of meters
• Magnetic Resonance Imaging (MRI) uses Radio wavelengths. It provides good
contrast between different brain tissues so it is very useful for imaging brain,
heart and cancer.
• It is much safer compared to CT Scan and X-Ray because it does not use
ionizing radiation.
13. MICROWAVES
• They are the shortest of the radio waves. Widely used as Radar (RAdio
Detection And Ranging) to determine range, altitude, direction or speed of
objects.
• Some microwaves have frequency similar to water molecules and are used in
Microwave ovens to cook food very quickly. They penetrate the food and heat
the inside of the food as much as outside. Presence of moisture increases
effectiveness.
• S-Band (2 - 4 GHz) is usually used in ovens which corresponds to 15 cm to 7.5
cm of wavelength. The screening mesh in the microwave oven door is
sufficiently fine (much smaller than 7.5 cm) that acts like a continuous thin metal
sheet and prevents the radiation from escaping the oven. It allows the user to
clearly see what’s inside because the wavelength of visible light is much
smaller.
14. SOME OF THE SOURCES OF LIGHT
• Solar System – All the colors of visible spectrum is produced at 5500 degrees
Celsius at sun’s surface
• Neon Lights – Gas filled tubes produce light when current is passed through it.
Neon gas produces red light. Different colors produce different colored lights
• LEDs – They are semiconductors light source. Early LEDs produced red,
orange, yellow and green lights
• Edison's Light Bulb – Carbon filament glows when heated by electric current.
