Advances in Hyperspectral Imaging
Authors: Jay Zakrzewski, Jay Julian (Headwall Photonics)
Abstract: Capturing precise spectral information from process manufacturing applications has traditionally
involved in-line or at-line single point spectral detection instrumentation which sample a very small area of
the overall product. Often, multiple sensors are necessary to cover a required spatial area, otherwise a time
consuming routine of many single measurements are necessary to spatially map the area of interest.
These options are costly due to redundant equipment, calibration concerns, and time.
Headwall Photonics will present several Hyperspectral sensor configurations which provide precise spectral
data of small spatial features viewed through a lens “push-broom” technique, or via a multi-channel fiber
optic collection at discrete measurement points simultaneously. Optimal imaging performance is obtained
using an imaging spectrometer design based on an all reflective, concentric f/2 spectrometer utilizing
aberration-corrected optics. In order to minimize stray light, the imaging spectrometer utilizes no prism or
Discussion: Hyperspectral imaging is a technique used to ascertain wavelength intensity mapping of a
scene with high spatial resolution. This blend of spectral data and spatial imagery can be analyzed for
color, chemical identification, material homogeneity and many other spectrophotometric measurements.
The spectral imaging accuracy of these systems also enables simultaneous spectral data collection of large
volumes of discrete optical fibers, each collecting spectra from unique locations.
Highly resolved spatial imaging performance combined with high spectral resolution over a broad spectral
bandwidth is proving to be valuable in tissue scanning, cancer detection, micro-well plate screening,
biomedical microscopy applications, nano particle research, hazardous materials detection, as well as
many other spectral sensing applications
Flexibility in design of advanced spectral imaging systems also allows trade off between spatial height and
spectral bandwidth dispersion, enabling either very high spectral resolution, or very large spatial field of
view. In general, today’s applications involve reflection, absorption, fluorescence, and Raman
The Headwall Photonics Hyperspec™ is most often employed as a scanning push-broom imager. For each
moment in time, or camera fram capture, a Field of View (FOV) observed by the objective lens is imaged
onto a tall slit aperture. The scene which fills the slit aperture is re-imaged through the patented aberration
corrected spectrometer with the wavelengths dispersed by a grating onto a 2D Focal Plane Array (FPA)
camera such as a CCD. One axis of the FPA (pixel-rows) corresponds to the imaged spatial positions
along the slit height in a 1:1 relationship. The second axis (spectral; pixel columns) corresponds to spectral
wavelength, which is linearly dispersed and calibrated.
Each 2D image (frame capture), is digitized by the FPA into a 2D data-array corresponding to the field of
view imaged through the slit. While scanning a wide scene, such as a human tissue sample, multiple 2D
image frame captures are taken while spatially stepping across the desired scene width, and these
individual frames are stacked like a deck of cards to produce a data file commonly called a Hyper-cube.
Each pixels value within this image Hyper-cube represents the spectral intensity plot of that pixels small
field of view on the scene. Figure 1 is a graphical representation of a Hypercube.
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Figure 1: Hyperspectral Cube (Source: AVIRIS Image Cube)
The resultant three dimensional matrix of data can be analyzed wholly, or interrogated
in several ways such as:
1. Vector: spectra at a position X, Y
2. Vector: X-profile at a particular wavelength
3. Vector: Y-profile at a particular wavelength
4. 2D Field: X, Y intensities at a particular wavelength (like a notch-filtered image of any wavelength)
5. Processed into pseudo-color rendered pictures identifying regions where the intensities of a certain
wavelength fall within prescribed parameters
6. Processed into pseudo-color rendered pictures identifying regions where a certain spectral
signature (spectral-waveform) fall within prescribed parameters
The following diagram (Figure 2) provides an example of the scanning approach in Push-broom scanning.
Figure 2. Push-broom scanning parameters
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The original holographic corrected grating installed in each Headwall Hyperspectral Imager is fabricated
using the same materials and process as Telcordia GR1221 telecommunications gratings validated for the
damp-heat, hi-temperature, and temperature cycling tests. The Hyperspec has been employed in several
demanding field applications. In addition to several proprietary industrial applications are the following
examples of military, research, and space qualified aerospace deployments:
• Hyperspec VS10 – Marine Optical Buoy (MOBY) Project; measurement of upwelling radiance and
downwelling irradiance at the sea surface and at three deeper depths; deployed by US National
Oceanic and Atmospheric Administration (NOAA); with initial deployment in 1993, this instrument is
responsible for calibration input of most of the US and international weather satellites for
forecasting conditions from El Niño weather patterns (paper available)
• Hyperspec VS30 – NRL airborne requirement for remote sensing and ocean color monitoring
• Hyperspec VS15 – USAF airborne mine detection in littoral zones
• Hyperspec VS15 – USN Predator-based project for Project Warhorse
• Hyperspec VS15 – NRL Ocean PHILLS (Portable Hyperspectral Imager for Low Light
• Hyperspec VS15 - Project Darkhorse utilizing VNIR sensor
• Hyperspec VS15 – AFRL LWIR sensor for polarimetric sensing for battlefield surveillance
• Hyperspec VS25 – Selected by NASA for International Space Station deployment
• Hyperspec VS25 – Optics deployed on Shadow UAV
• Hyperspec VS – Custom UV/MCP unit deployed for AFRL missile plume tracking
• Hyperspec VS50 – Airborne SWIR sensor
• Micro-Hyperspec VNIR and NIR – Introduced in 2006 for UAV and SUGV deployment
• Hyperspec VNIR – NASA augmentation for AVIRIS
Example of Hyperspec™ Images
The following is an example of a rendered image of a Natural Ruby utilizing the Hyperspec C-Series
spectrometer with Headwall Photonics image processing software for Hyperspec . The rendered images
depict were certain spectral response feature reside within the sample.
Natural Ruby (Kenya)
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Applicable to Multichannel Fiberoptic Array Detection and Multipoint Spatial Mapping
In a typical application the input slit is a physical aperture located at the image plane of the objective lens,
but this slit may also be comprised of several fiber optics creating a linear-array launch. The pinhole array
mask is a good approximation of this, and allows fiber array performance to also be evaluated. A fiber array
Hyperspec™ can be used as a staring array or a multi-channel single point spectrometer as shown below.
Headwall has several configurations to offer for application specific performance.
Individual spectra generated for each station
Process monitor station # 1
Process monitor station # 2
Process monitor station # 3
Process monitor station # 4
Process monitor station # 5
#1 #2 #3 #4 #5
Process Monitoring Stations
Conclusion: High performance spectral imaging has moved from advanced military applications to more
affordable commercial solutions for a wide variety of applications. The high accuracy, sensitivity and
dynamic range of totally reflective hyperspectral imagers is enabling research and commercial
development of advanced spectral analysis techniques. Headwall Photonics has innovated several cost
effective and performance differentiated sensor platforms which provide superior performance and flexibility
to allow quick integration into traditional hyperspectral imaging techniques, as well as hyperspectral Raman
spectroscopy. These systems support push-broom line scanning, multi-channel fiber optic and large
volume fiber optic spatial mapping of spectral content within a sampled area.
For more information, please contact:
Director, Business Development
Headwall Photonics, Inc.