Editorial Feature

Detecting Fugitive Environmental Contaminants with the Use of Imaging Spectroscopy

Background
What is Imaging Spectroscopy?
Theory Behind Hyper-Spectral Imaging
Traditional Multi-Spectral Remote Sensing vs. Hyper-Spectral Remote Sensing

Background

The intentional or accidental release of contaminants into the environment is an inevitable consequence of human activity. Industrial, mining and even natural processes can cause the release of substances into the air, land and water which may be harmful to environmental quality.

In addition, products such as oil and other petroleum can result in significant health hazards when it is released. Accidental releases of oil and related products into the environment threaten public health and safety through contamination of drinking water, fire and explosions, diminished air and water quality, destruction of recreational areas, and compromised agriculture.

What is Imaging Spectroscopy?

Imaging Spectroscopy also commonly referred to as hyper-spectral remote sensing, is an imaging technique that is capable of identifying materials and objects in the air, land and water, based on the unique spectral reflectance patterns that result from the interaction of solar energy with the molecular structure of the material. Hyper-spectral remote sensing is a relatively new scientific capability within the field of remote sensing, and is currently making the transition from purely research and development into commercial applications.

Due to the advancement in sensors and electronic design, hyper-spectral remote sensing instruments are able to collect reflected and emitted electromagnetic energy in hundreds of discrete spectral channels. This allows a near-continuous recording of hundreds of very narrow spectral bands across the reflected and emitted parts of the electromagnetic spectrum.

Theory Behind Hyper-Spectral Imaging

Hyper-spectral imaging and analysis techniques are related to a special class of spectroscopic analysis called reflectance spectroscopy. Reflectance spectroscopy is the study of energy as a function of wavelength that has been reflected from or scattered by a solid, liquid or gas.

It differs from other spectroscopic techniques in two primary ways. First, the energy is reflected or scattered back to the sensing device. Second, reflectance spectroscopy, especially as applied to overhead remote sensing, is limited to the .4 - 2.5 µm range of the electromagnetic spectrum where solar radiation is passed through atmosphere.

Traditional Multi-Spectral Remote Sensing vs. Hyper-Spectral Remote Sensing

Traditional multi-spectral remote sensing instruments collect data in a few selectively placed, broad portions of spectrum. On the other hand, hyper-spectral remote sensing instruments collect a discrete image for hundreds of narrow bands in the magnitude of around 10 nm, resulting in an image with hundreds of separate bands. A further development is the Ultra-Spectral Remote Sensing collects data in thousands of very narrow bands.

Most materials on the surface of the earth contain characteristic absorption and reflectance features based on their molecular structure. These absorption and reflectance features can be identified through the unique spectral trace, or spectra, of that particular substance.

This unique interaction between energy and matter in each pixel of a hyper-spectral image is recorded. By comparing the plot of spectral responses through the hundreds of spectral channels with a library of known spectral reflectance, the imaging scientist can now identify specific substances such as minerals, chlorophyll, dissolved organics, atmospheric constituents, and specific environmental contaminants. Other applications include water and air quality analysis, vegetative species identification, and fate and transport modeling.

Source: AZoOptics

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