Energy and EM spectrum

The energy that is around us is called electro-magnetic radiation or EM radiation, and it behaves as waves. The different types of energy are represented by different wavelengths, like long radio wavelengths, or short x-ray wavelengths. A measure of energy relating to wavelength is frequency, which is what you might think of when describing radio waves. When you tune into a radio station, or a channel on VHF, you are finding the specific frequency of the energy that is carrying the signal (eg. 1230 AM), and when your sensor (the radio) is tuned to that frequency, suddenly you can hear it! With Earth observation sensors, we can detect the energy that the sensor is “tuned” to. 

Video

Watch the following video to see the types of energy around us.

Organizing waves in order of wavelength shows us the range or “spectrum” of energy and lets us understand how energy properties and behaviour change with wavelength 

Knowing about  the wavelengths you’re working with will be important when we are interpreting imagery! A key understanding for our work is that longer wavelengths can penetrate through the atmosphere and clouds, so we have a way to view the Earth surface even when it is cloud covered. Compare the types of energy shown here and their wavelengths. 

Included in the EM spectrum is a small section which contains the wavelengths of light that our eyes can detect and “see”. We call this the visible spectrum. The longest visible wavelength is red and the shortest is violet. Think of a rainbow – the smallest inside arc is the violet and blue colours, and the largest outside arc is the red. In between, the colours are distributed according to their wavelength. 

Beyond the visible wavelengths are energy wavelengths which are “invisible” to our eyes, but can be detected by other remote sensing instruments and used to our advantage. In this image, the sensor is detecting heat, which is thermal electronic radiation with longer wavelengths than visible light.

Thermal image of wolf. Warmest areas appear light pink and red, coolest are dark blues and bright pink. USGS. Wikimedia Commons

Sometimes other animals can detect radiation that is invisible to humans – like most birds and bees, who have the ability to see ultraviolet light. Ultraviolet light has a wavelength even smaller than visible light – just beyond the violet light and smaller than what humans can see! Humans need to use remote sensing instruments to see ultraviolet light and when we do, we get additional information about the object  we are viewing. 

By Wild_Strawberry_Fragaria_vesca_spectral_comparison_Vis_UV_IR.jpg: Dave Kennardderivative work: Jullit31 – This file was derived from: Wild Strawberry Fragaria vesca spectral comparison Vis UV IR.jpg:, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=29927128

Activity 

Put the energy in the correct order based on the wavelengths (Ian they are currently listed longer to shorter)

• radio waves
• microwaves
• infrared
• red
• yellow
• blue
• violet
• ultraviolet
• x-ray
• gamma ray