Abstract
Over the past 20 years, hyperspectral microscopy has grown into a robust field of analysis for a number of applications. The visible to near-infrared (VNIR; 400 to 1000 nm) region of the spectrum has demonstrated utility for the characterization of healthy and diseased tissue and of biomolecular indicators at the cellular level. Here, we describe the development of a hyperspectral imaging (HSI) microscope that is aimed at material characterization to complement traditional stand-off, earth remote sensing with hyperspectral sensors. We combine commercial off the shelf technology to build an HSI microscope to collect spectral data with illumination provided by a tunable laser. Hyperspectral imaging microscopy (HIM) facilitates detailed examination of target materials at the subcentimeter spatial scale. The custom-built, laser illumination HSI microscope covers the NIR to shortwave infrared (NIR/SWIR; 900 to 2500 nm) solar-reflected spectral range. It is combined with a separate VNIR sensor (400 to 900 nm) that utilizes quartz–tungsten–halogen lamps for illumination. The combined sensors provide a means to collect >10,000 s of spectra in the full VNIR/SWIR spectral range from both pure substances and precisely engineered linear and nonlinear mixtures. The large abundance of spectra allows for a more detailed understanding of the variability and multivariate probability distributions of spectral signatures. This additional information aids in understanding the variability observed in ground truth spectra collected from portable spectrometers, and it greatly enhances sample description and metadata content. In addition, HIM data cubes can serve as proxies, as “microscenes,” for systems engineering applications such as trade studies for HSI acquired by air- and space-borne sensors.
Highlights
Hyperspectral remote sensing (HRS), known as imaging spectroscopy or hyperspectral imaging (HSI), is rapidly emerging as a distinct and key discipline in the science of Earth and planetary observation
Special charge-coupled device (CCD) cameras combined with gratings, prisms, or interferometers enable solar-reflected energy (350 to 2500 nm) and emitted (7500 to 13,500 nm) energy to be separated into hundreds of narrow, contiguous bands that capture the interactions of photons with the atomic and molecular structure of a target material
While HSI can effectively detect and identify a target material embedded in background clutter, determining how well this can be achieved as a function of various measurement conditions or parameters can be a challenge.[50]
Summary
Hyperspectral remote sensing (HRS), known as imaging spectroscopy or hyperspectral imaging (HSI), is rapidly emerging as a distinct and key discipline in the science of Earth and planetary observation. When calibrated (spectrally and radiometrically) and processed to remove sensor and atmospheric artifacts, each pixel in the image is expressed as a vector through the stack that represents a spectrum essentially identical to that achieved under laboratory conditions.[1] Figure 1 graphically depicts the concept of a hyperspectral image stack comprised of hundreds of bands of imagery, collected at slightly different wavelengths across the solar reflected spectrum from 390 to 2500 nm. There exists a need in the remote sensing community to characterize materials with high spatial resolution imaging spectroscopy, and to do this over the full solar-reflected (350 to 2500 nm) spectral range.
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