The basics of optical spectroscopy for industrial and remote sensing

VNIR technology

Near-infrared spectroscopy is the study of interactions of electromagnetic radiation with chemical bonds of materials – the energy is either reflected, transmitted, or absorbed. Spectra are produced when the bonds in organic materials or geologic minerals interact with this energy. Spectroscopy uses a ratio between reflected energy (or absorbed energy) relative to the total amount of energy that illuminates the sample. ASD portable VNIR products use 2151 wavelength intervals and combine them into a continuous spectral signature.

ASD spectrometers utilize the optical spectroscopic region of the electromagnetic spectrum (from 350 to 2500 nanometers). ASD instruments measure over the 350 to 2500 nm wavelength range. Unlike other measurement tools that use X-ray or ultraviolet, energy in this wavelength range is non-hazardous. Reflectance spectra can be used to quickly determine a material’s properties without altering or even coming in contact with the sample. These instruments are capable of examining irregular surfaces with the same ease as a carefully prepared sample and can also be used to analyze multiple constituents when utilizing a quantitative calibration model in a single 5-second scan. The technique is non-destructive and requires little or no sample preparation. Read more about measuring a product using ASD near-infrared (NIR) in this blog post.

These highly flexible analyses are used with a broad range of research and industrial process applications. Long considered a staple technology in earth remote sensing, reflectance spectroscopy has become popular within industrial markets. It is known for being a cost-effective tool for measuring materials to obtain actionable information to help optimize processes, manage costs and improve research.

Remote sensing

This application is defined as ‘the science and art of identifying, observing and measuring an object without coming into direct contact with it’¹. Often, the sun is used to illuminate the sample, or alternatively, a quartz-halogen lamp can also be used to illuminate the material. In many cases, the spectra are acquired and information created without being in physical contact with the sample.

Remote sensing can aid in mineral exploration, art restoration, archeological studies, agricultural analysis for the determination of plant health, water status, fertilizer optimization, and many more.

ASD instruments, specifically the FieldSpec range, often use the sun as a source of illumination. Visible, near-infrared, and short-wave infrared sensors in the FieldSpec collect the energy reflected from the sample as a spectrum. These spectra are then used to differentiate between various materials such as plants or minerals. FieldSpec spectroradiometers can be optionally calibrated to produce radiance and irradiance measurements of absolute energy. This allows the spectra to be used in conjunction with overflight or orbital sensors contained in satellites. They can also be used interchangeably as spectrometers by referencing with a calibrated or uncalibrated Spectralon reference panel to obtain a spectral signature.

A spectral signature is like a fingerprint. Different surface types such as water, bare ground, and vegetation reflect radiation differently in various channels. Essentially, the configuration of the reflectance spectra allows the spectra to be used to recognize a type of material.

Ultimate Flexibility

FieldSpec is the most flexible spectrometer available today. In addition to remote sensing applications, it can also be used to create multivariate predictive models that can automatically predict material composition each time a spectrum is acquired! The FieldSpec can be used whenever and wherever it is needed, including in the laboratory or in the field as it can operate both online voltages or using a battery pack. Outstanding signal-to-noise means that portability doesn’t place a penalty on performance.

About ASD – a Malvern Panalytical brand

ASD is a Malvern Panalytical brand and delivers optical spectroscopy instruments for remote sensing, mining, and other industrial markets. They complement and extend the company’s offering towards scientific and industrial customers adding portable, handheld, benchtop, and online products.

ASD optical spectrometer and spectroradiometer instruments have many diverse application uses. They can be employed in various market sectors, such as environmental (FieldSpec), mining (TerraSpec), and food & pharma (LabSpec) and are occasionally used in forensics, cosmetics, and building materials.

References

1. Evelyn L. Pruitt, US Office of Naval Research