102. Let's Talk...Wavelengths and Remote Sensing

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Writing about stuff like remote sensing, satellites, and real-time imagery is all great fun up to a point. It's when the experts of these fields start to discuss the more technical aspects that things can get uncomfortable - like colour bands, Normalized Difference Vegetation Index or 'false' colour images (huh?!)

This post is an attempt to explain one of the concepts which geospatialists may need to understand if they are ever to get stuck in an elevator with a group of physicists.

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Imagery is captured using either active sensors or passive sensors. These sensors record the wavelengths of visible light which are emitted from their point of focus.

A wavelength refers to the means by which light is measured. One wavelength refers to the distance between two successive wave troughs or crests. As such, light is categorized into different types within the electromagnetic spectrum - with each type depending on the distance between the emitted wavelengths.

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The largest types of waves are called radio waves. These are used to transmit television and radio programmes.

They can either be very big or very small.



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After radio waves, we get into the waves for optical communications.

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The first optical waves are called infrared waves. These are somewhat smaller than radio waves (about the width of a pinhead) and they emit heat. A good example of infrared light is the type of kitchen lights used to keep food warm in a restaurant.



After infrared waves, we're at the point when waves start to get really, really, really small...as in the size of molecules and atoms and nuclei.

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First, come the type of waves which keep map-makers in employment - visible waves.

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As the name implies, these are the only waves in the electromagnetic spectrum which we can actually see, and each colour in the spectrum appears in the same sequence as it would in a rainbow. Red has the longest wavelength and violet has the shortest wavelength.


A blink of the eye later, we're back into the invisible wavelengths territory!


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First up, and moving on from the final colour in the visible spectrum, is ultraviolet, or UV waves.

These type of waves come from things like the sun or high power welding machines. Due to the radiation emitted, UV waves can be very dangerous if over-exposed to them!


After ultraviolet, we're into the world of X-Rays.


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These are a pretty obvious one. However, if you want to learn more about X-Rays just ask your local doctor! I'm sure he or she will be delighted to discuss the electromagnetic spectrum.

Especially if it's on the clock!




The final and smallest wave which we know of is the Gamma Ray.


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However, unless you are work in the advanced medical sciences or spend your time fighting aliens, you probably have little use for these! Bew Bew!



The key thing to remember when it comes to the electromagnetic spectrum is that, although visible waves are the only ones which humans can see, the other categories of waves are, thanks to more sophisticated sensor technology, being captured and put to greater use by remote sensing experts. Ultimately, this will help us to build up a more comprehensive understanding of what is going on with our planet.

Exciting times.

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