Posted in | Imaging | Fibre Optics

New Portable Spectrometer Captures Real-Time Hyperspectral Data Instantly

While there is so much to see and learn about Earth, typical photos from space do not show the planet in all its glory.

Bundles of optic fibers in Rice University’s TuLIPSS spectrometer deliver spatial and spectral data to a detector in an instant. That data can then be processed for quick environmental or biological analysis. (Image credit: Modern Optical Instrumentation and Bio-Imaging Laboratory)

To expose the details that cannot be seen with the naked eye, engineers at Rice University are developing a new, portable spectrometer that can be easily fixed to a compact satellite, flown on a drone or an airplane, or one day can even be held in the hand.

Bioengineer Tomasz Tkaczyk and his coworkers at Rice University’s Brown School of Engineering and Wiess School of Natural Sciences have reported the initial outcomes from a NASA-funded project to create a compact, state-of-the-art spectrometer that has exceptional versatility. The article has been published in Optics Express.

A spectrometer can be defined as a device that collects light from a scene or an object, isolates the colors, and measures them to establish the chemical contents or other properties of what it visualizes.

The new device, known as the Tunable Light-Guide Image Processing Snapshot Spectrometer, or TuLIPSS in short, is different from existing systems that typically scan a scene or an image line-by-line and for subsequent reassembly. On the other hand, the TuLIPSS spectrometer will allow scientists to rapidly capture data across the near-infrared and visible spectrum.

Every pixel in the hyperspectral images generated by the TuLIPSS spectrometer includes either spatial or spectral data. In this case, the “pixels” are a countless number of optical fibers—flexible light guides that transmit the components of the image to a detector. Since they can reposition the fibers, the scientists can modify the balance of image and spectral information transmitted to the detector.

For instance, the device can be adjusted to determine the chemistry of a tree to check if it is diseased or healthy. The device can do the same for a single leaf, a cell, a planet, or a farm or neighborhood. In the case of continuous-capture mode—similar to the motor drive of a camera—it can demonstrate the way the spectral “fingerprints” in an immobile scene alter in due course, or alternatively collect the real-time spectral signature of a lightning bolt.

TuLIPSS is a special instrument because it operates just like any other camera, capturing all the hyperspectral information—what is called a data cube by the researchers—immediately, stated Tkaczyk. This implies that an orbiting satellite or airplane can rapidly capture a picture of the ground and thus prevent motion blur that otherwise would distort the data. That data will be filtered by onboard processing, which would subsequently send only what is needed back to Earth, thus saving both energy and time.

This would be an interesting tool in the case of an event like Hurricane Harvey. When there’s a flood and potential contamination, a device able to fly over a reservoir could tell if that water is safe for people to drink. It would be more effective than sending someone to a site that may be hard to reach.

Tomasz Tkaczyk, Associate Professor of Bioengineering, Department of Bioengineering, Rice University

A lens in a typical camera directs the incoming light onto a sensor chip and then changes the data into an image. In the TuLIPSS spectrometer, the lens directs the same light onto a middleman—that is, the bundle of optical fibers.

In the present model, these optical fibers collect 61 spectral channels and over 30,000 spatial samples in the 450–750 nm range—basically, a countless number of data points—divided by prisms into their component bands and transmitted to a detector. Subsequently, the detector feeds these data points to software that reintegrates them into the preferred spectra or images.

At the input, the fiber array is closely packed, while at the output, they are reorganized into separately addressable rows, with gaps existing between them to prevent overlap. Spacing the rows enables scientists to adjust spectral and spatial sampling for particular applications, stated Tkaczyk.

First author Ye Wang, who received her doctorate this year at Rice University, and her coworkers meticulously developed the prototype, positioning and assembling the bundles of optical fibers manually. The team utilized scenes in and around the Rice University to test it, rebuilding pictures of buildings to customize the TuLIPSS spectrometer and capturing the spectral images of trees in the Rice University campus to “detect” their species. In addition, the researchers effectively examined the health of numerous plants using only spectral data.

Unlimited capture of images of the moving traffic in Houston demonstrated the potential of the system to visualize which type of spectra are moving over time (for example, changing traffic lights and moving vehicles) and which are steady (everything else). This experiment turned out to be a handy proof-of-concept to demonstrate how effectively the TuLIPSS spectrometer is able to filter motion blur in dynamic conditions.

According to co-author David Alexander, a professor of astronomy and physics and director of the Rice Space Institute, the investigators have already started discussions with the city of Houston and the Kinder Institute for Urban Research of Rice University about testing the TuLIPSS spectrometer in the city’s aerial studies.

Since we need to test TuLIPSS anyway, we want to do something useful,” he stated and proposed that a hyperspectral map of the city can possibly expose the way the urban landscape is altering, differentiate parks from buildings, or map pollen sources. “In principle, regular flights over the city will allow us to map out the changing conditions and identify areas that need attention.”

Upcoming versions of the TuLIPSS spectrometer will be valuable for algae blooms, for atmospheric and agricultural analysis, and for other similar environmental conditions where rapid acquisition of data will be useful, suggested Tkaczyk.

The real challenge has been to decide what to focus on first. Ultimately, we want to be successful enough that the next phase of development pushes us closer to flying TuLIPSS in space.

David Alexander, Study Co-Author, Professor, and Director, Department of Physics and Astronomy, Rice Space Institute, Rice University

Co-authors of the study are Rice research scientists Michal Pawlowski, Shuna Cheng, and Jason Dwight; postdoctoral researcher Razvan Stoian; and graduate student Jiawei Lu. Tkaczyk is an associate professor of bioengineering, and Alexander is a professor of physics and astronomy.

Initial funding for the project came through a $2 million, 3-year award to Rice University as part of $53 million in grants by NASA’s Science Mission Directorate and its Earth Science. Technology Office to develop novel technologies and instruments for future Earth science methods and observations.

Continuous capture images of moving traffic in the Houston neighborhood around Rice University shows how the TuLIPSS spectrometer filtersmotion blur in dynamic situations. The full-color video is a composite of the filtered spectral data captured by the device. The portable spectrometer has proven its ability to capture far more data much quicker than other fiber-based systems. (Video credit: Modern Optical Instrumentation and Bio-Imaging Laboratory)

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