Hyperspectral Imagers for Drones

Researchers used 3-D printing to create hyperspectral imagers that are light enough to use on a drone. The imager is the small protrusion on the bottom of the drone’s body. (Source: J. Fortuna, Norwegian Univ. of Science and Technol.)

In a new study, researchers used 3D printing and low-cost parts to create an inex­pensive hyper­spectral imager that is light enough to use onboard drones. They offer a recipe for creating these imagers, which could make the tradi­tionally expensive ana­lytical technique more widely acces­sible. Hyperspectral imagers produce images like a tradi­tional color camera but detect several hundred colors instead of the three detected by normal cameras. Each pixel of a hyper­spectral image contains infor­mation covering the entire visible spectrum, providing data that can be used, for example, to automa­tically detect and sort objects or measure ocean color to map harmful algae blooms. Tradi­tional hyper­spectral imagers can cost tens of thousands of dollars and are very bulky and heavy.

The researchers describe how to make visible-wave­length hyper­spectral imagers weighing less than half a pound for as little $700. They also demon­strate that these imagers can acquire spectral data from aboard a drone. “The instru­ments we made can be used very effec­tively on a drone or unmanned vehicle to acquire spectral images,” said research team leader Fred Sigernes of Univer­sity Centre in Svalbard (UNIS), Norway. “This means that hyper­spectral imaging could be used to map large areas of terrain, for example, without the need to hire a plane or heli­copter to carry an expen­sive and large instru­ment.”

A desktop 3D printer greatly eased the process of making the custom optics holders needed for the imagers. “Making items in metal is time consuming and can be very expen­sive,” said Sigernes. “However, 3D printing with plastic is inexpen­sive and very effec­tive for making even complex parts, such as the piece needed to hold the grating that disperses the light. I was able to print several versions and try them out.” The hyper­spectral imagers uses precise line-scanning to build up a spectral image. The researchers added a stabi­lization system to the setup so that a drone’s movement would not distort the image as it was being generated.

“Push-broom hyper­spectral imagers typically require expen­sive orien­tation stabi­lization,” explained Sigernes. “However, you can now buy very inexpen­sive gyro­scope-based, electro­nically stabi­lizing systems. The advent of these new systems made is possible for us to make inex­pensive hyper­spectral imagers.” The researchers made several proto­types by using 3D printing to create plastic holders that precisely position small, light­weight commer­cially available cameras and optical components. They tested one of the instru­ments onboard an octo­copter drone equipped with a two-axis elec­tronic stabi­lizing system. The hyper­spectral imager performed well and was able to detect landscape features such as vege­tation and bodies of water.

They also performed handheld tests with the hyper­spectral imagers and three-axis electronic stabi­lizing systems. For one experiment, they swept the imager across a computer screen dis­playing a fruit collec­tion, acquiring 571 spectro­grams in 22 seconds. These feasi­bility tests showed that 3D printing is accurate enough to produce proto­type parts for optical systems. The printed plastic parts were light weight and strong enough to keep the overall system light and small, which is important for use with drones. After testing, metal versions of 3D printed parts could be ordered if desired to create imagers that would be more durable.

Although the new imagers don’t provide the sensi­tivity of tradi­tional hyper­spectral imagers, their per­formance is suffi­cient for mapping terrain or detecting ocean color in daylight. The researchers are now working to improve sensi­tivity by making slightly larger versions of the instru­ments that would still be small and light enough for use on drones. Improving the sensi­tivity of the imagers will provide higher quality data. “There are many ways to use data acquired by hyper­spectral imagers,” said Sigernes. “By lowering the cost of these instru­ments, we hope that more people will be able to use this ana­lytical technique and develop it further.” (Source: OSA)

Reference: F. Sigernes et al.: Do it yourself hyperspectral imager for handheld to airborne operations, Opt. Exp. 26, 6021 (2018); DOI: 10.1364/OE.26.006021

Link: Kjell Henriksen Observatory, University Centre in Svalbard UNIS, Longyearbyen, Norway

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