A good way to work with materials, identify them, or define their properties is to study how light interacts with them. This study of light interaction with materials is called spectroscopy. Spectroscopy examines how light behaves in the target and recognizes materials based on their different spectral signatures. These spectral signatures can be identified from the spectrum of the material. Spectrum describes the amount of light in different wavelengths.
It shows how much light is emitted, reflected, or transmitted from the target. To put it in short, the spectrum tells how much of a certain color this light contains. The usual way to present spectrum is a graph on a scale of intensity and wavelength. Spectral signatures can be compared to fingerprints, just like fingerprints can be used to identify a person, spectral signatures can be used to identify a material.
Let’s examine the reflected light in more detail. To study the light, one needs an instrument called a spectrometer. It’s an instrument that splits the incoming light into a spectrum. In this example, the light going through a spectrometer is reflected, and the result is therefore called a reflectance spectrum. Measuring the reflectance spectra is the most common way to use hyperspectral imaging.
Hyperspectral imaging uses an imaging spectrometer to collect spectral information. This device is also called a hyperspectral camera. With a hyperspectral camera, we measure thousands or hundreds of thousands of spectra instead of a single spectrum. The collected spectra are used to form an image of the target so that each image pixel includes a complete spectrum. By doing this, we are able to get answers to questions such as what, based on the spectrum, and where, based on the location.
We can pick any position from the target to get the information. This means a large amount of accurate information. The data that hyperspectral imaging provides is called a data cube because the hyperspectral data is actually three-dimensional. In the next tutorial, called What Hyperspectral Imaging Provides, we will use a book example to explain it.