Electromagnetic Radiation

Electromagnetic Energy Interactions

When the energy being remotely sensed comes from the Sun, the energy:

• Propagates through the vacuum of space
• Interacts with the Earth's atmosphere, surface, and atmosphere (reflected, absorbed, transmitted);
• Reaches the remote sensor (interacts with various optical systems, filters, emulsions, or detectors);

Electromagnetic Radiation

Transfer of energy from one body to another in the form of electromagnetic waves is referred to as Electromagnetic Radiation.

To understand how electromagnetic radiation is created, how it propagates through space, and how it interacts with other matter, it is useful to describe the processes using two different models popularly known as Electromagnetic Radiation Models: 

• the wave model;
• the particle model

Wave Model of EM Energy

An electromagnetic wave is composed of electric and magnetic vectors that are orthogonal to one another and travel from the source at the speed of light.

Properties of EMR

Frequency: the number of wavelengths that pass a point per unit time. (unit = hertz)

Wavelength: the mean distance between maximums (or minimums) (unit = m)

Common units: micrometers (µm) or nanometers (nm) 

One cycle per second is termed one hertz (1 Hz)

Frequency is inversely proportional to wavelength. hence, the longer the wavelength, the lower the frequency, and vice-versa.

Relationship of Wavelength and Frequency

Electromagnetic Wavelengths and their corresponding measurement units