Electromagnetic Spectrum

The electromagnetic spectrum is a range of all electromagnetic waves arranged according to frequency and wavelength. The sun, earth, and other bodies radiate electromagnetic energy of varying wavelengths. Electromagnetic energy passes through space at the speed of light in the form of sine waves. The wavelength is the distance from wavecrest to wavecrest.

Radio: radio stations emit into the air

Microwaves: To learn about the structure of nearby galaxies

Infrared:  Our skin emits infrared light

Visible: This is the part that our eyes see.

Ultraviolet: Sun is a source of ultraviolet radiation and that cause our skin to burn

X-rays: Doctor uses them to look at human bones or teeth.

Gamma-rays: Radioactive materials (some natural and others made by man in things like nuclear power plants)

The micron is the basic unit for measuring the wavelength of electromagnetic waves. The spectrum of waves is divided into sections based on wavelength. The range of visible consists of the narrow portion of the spectrum, from 0.4 microns (blue) to 0.8 microns (red).

Visible light is a very narrow part of the EM spectrum, whereas remote sensing equipment can obtain information from a much greater potion of the spectrum. Each part of the EM spectrum defined in the diagram has particular advantages in remote sensing. Landscape features typically absorb some of the incoming solar radiation and reflect some

The portion depending on the nature of the feature, for example;

 Water absorbs near infrared

 Some features emit their own radiation, such as heat from hot springs, which shows up bright on thermal infrared imagery

Knowing the response of various features under various conditions is important for interpreting remote sensing imagery.