All of the energy from the Sun that reaches the Earth arrives as solar radiation, part of a large collection of energy called the electromagnetic radiation spectrum. Solar radiation includes visible light, ultraviolet light, infrared, radio waves, X-rays, and gamma rays. Radiation is one way to transfer heat.

As shown in the illustration below, there are three main sources of electromagnetic radiation that are used in remote sensing:

• solar radiation, in other words natural radiation that originates from the sun.
• terrestrial radiation, in other words natural radiation emitted by the Earth’s surface.

Examples of EM radiation include radio waves and microwaves, as well as infrared, ultraviolet, gamma, and x-rays. Some sources of EM radiation include sources in the cosmos (e.g., the sun and stars), radioactive elements, and manufactured devices.

The visible light spectrum is the segment of the electromagnetic spectrum that the human eye can view. More simply, this range of wavelengths is called visible light. Typically, the human eye can detect wavelengths from 380 to 700 nanometers.

Our Protective Atmosphere However, the Earth’s atmosphere protects us from exposure to a range of higher energy waves that can be harmful to life. Exposure to these high-energy waves can alter atoms and molecules and cause damage to cells in organic matter.

The propagation of electromagnetic waves either in a certain medium or in vacuum is due the the mutual changes between the electric and magnetic field. These variations in electric and magnetic fields fields lead to the transfer of the energy which is carried by the EM wave.

Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth’s atmosphere at a close, but slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents.

Speed of Electromagnetic Waves All electromagnetic waves travel at the same speed through empty space. Electromagnetic waves travel more slowly through a medium, and their speed may vary from one medium to another. For example, light travels more slowly through water than it does through air (see Figure below).

Matter wave can neither leave the particle nor can they move in vacuum.

Material wave (de Broglie wave) can travel in vacuum.

A is a disturbance that transfers energy from one place to another. Waves can transfer energy over distance without moving matter the entire distance. For example, an ocean wave can travel many kilometers without the water itself moving many kilometers. It is the disturbance that travels in a wave, transferring energy.

Waves come in two kinds, longitudinal and transverse. Transverse waves are like those on water, with the surface going up and down, and longitudinal waves are like of those of sound, consisting of alternating compressions and rarefactions in a medium.

Electromagnetic Wave

• Microwaves.
• X-ray.
• Radio waves.
• Ultraviolet waves.