Hyperspectral imaging uses uses visible light, ultraviolet, and infrared light to record an image.
Your eyes are capable of processing light in a narrow range of light waves that we refer to as visible light. You can see different colors because your eyes can sense light at different wavelengths. For example, the color red has a relatively long wavelength and violet, at the top end of the visible spectrum, has a relatively short wavelength. There are wavelengths outside of the range of visible light and our eyes simply cannot detect those wavelengths. A good example is UVA and UVB that is emitted by the sun. Although we can't see UVA and UVB light, we know that we need to protect our skin from UVA and UVB because it causes sunburn. Sunblock lotion blocks the absorption of UVA and UVB light, which prevents your skin from burning. The sunblock lotion works with a very narrow spectrum of invisible light.
Infrared light waves have a longer wavelength than the red that our eyes can see and are therefore invisible to us. You are already familiar with an application of infrared light - your TV's remote control uses infrared light. You also might familiar with infrared imaging where an image of someone's body heat is shown using various shades of red. Infrared light is also used for night vision cameras and other devices.
The light that you see is really reflected by the object you are viewing. When you look at a red apple, the apple's skin actually absorbs all of the light around it and reflects only some of the the light, in this case in the red spectrum, so you see the apple's red color. The color white is visible when all of the light shining on an object gets reflected, and a black object reflects very little light. The range of light an object reflects is referred to as its spectrum. A red apple's spectrum centers around red wavelengths - so you won't see any green, for example.
Physicists, a long time ago, figured out objects that are made out of different molecules reflect light differently. Something that's red is made up of things that are different when compared with another object that's black. Physicists developed tables that correlate the color of reflected light to an object's composition. Why would a physicist bother with figuring out what something is made out of based only on the light it reflects?
While you can pick up an apple and figure out what it is made out of, you can't do the same with something that's much bigger or further away. When dealing with things that are too big, too far, or too fast to capture and analyze, physicists can just look at the light that the object reflects to get a very good idea of its composition. A great example is a star, like our Sun. We know that the Sun is made up of two main elements - hydrogen and helium. We did not send someone to the Sun to take a sample because the Sun is far too hot to get close enough to get a sample of its surface. We learned about the Sun's composition by looking at the light that it emits.
A spectrometer is a device that's capable of measuring and charting information about waves, like light waves. Hyperspectral imaging combines visible light and infrared light and uses a spectrometer to analyze the light to determine the composition of whatever you're viewing. Infrared imaging is an excellent tool; however, it has its practical limitations. Scientists figured out that they could combine infrared imaging with a mathematical operation called a Fourier Transform. A Fourier Transform can decompose a signal into the parts that make it up. For example, a Fourier Transform of a number of notes played at the same time on a piano would be the individual notes that created the chord. Fourier Transforms for things like analysis of frequencies of light ignore time, focusing only on the wavelengths of light without regard to time. This is an important characteristic because analysis of light is concerned with the spectrum at an instant rather than its change over time.
When you combine a Fourier Transform (FT) with infrared light (IR) and add a spectrometer, you end up with a FTIR spectrometer. FTIR spectrometers are very practical because they can determine the composition of something regardless of whether the thing you are analyzing a solid, liquid, or gas.
Practical applications if FTIR include hyperspectral imagers that are capable of sensing pollutants in the air, the composition of soil, and the health of forests. The beauty of FTIR is you just need to point the FTIR spectrometer at the object you want to analyze and the spectrometer does the rest. Researchers have been using the remote sensing capabilities of hyperspectral imagers using FTIR of many years to find oil just under the surface of the ground. A researcher attaches an FTIR spectrometer to the bottom of a small plane and flies over an area, collecting data as the plane passes over the area of interest. There's no need to land or take soil samples, making it easy to analyze very large areas in a short time.
Even with its advanced applications, hyperspectral imaging is still relatively new and its full potential has not yet been realized.
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