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12 Platform one April/May 2018 | Unmanned Systems Technology Researchers at the University of Norway have used 3D printing and low-cost parts to create an inexpensive hyperspectral imager that is light enough to use on small UAVs (writes Nick Flaherty). Each pixel of a hyperspectral image contains information covering the entire visible spectrum, providing data that can be used to measure ocean colour to map harmful algae blooms for example, or monitor crops. Traditional imagers can cost tens of thousands of dollars, however, and can be bulky and heavy. The new design though weighs less than 200 g and costs under $700 but reduces the spectral range to 1.4-5 nm from visible light to near infrared. “Our instrument can be used very effectively on an unmanned vehicle to acquire spectral images,” said research team leader Fred Sigernes at the University Centre in Svalbard. A desktop 3D printer was used to generate custom holders for the specialist optics in the camera. “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. We were able to print several versions and try them out.” The imager uses a push-broom technique with a diffraction grating and line-scanning architecture to build up a spectral image. This needed a stabilisation system so that any UAV movement would not distort the image as it was being generated. “Push-broom hyperspectral imagers typically require expensive orientation stabilisation,” explained Sigernes. “However, you can now buy inexpensive gyroscope-based, electronically stabilising systems. That made it possible for us to make our imager.” The researchers made four prototypes with different sensors ranging from a colour CCD video camera head from Sony, a CamOne Infinity action camera to two monochrome industrial CMOS image sensors. The main differences between the prototypes are the type of detectors and how they are mounted to the grating housing. The imager was tested with a two- axis electronic stabilising system on an octocopter, and was able to detect landscape features such as vegetation and bodies of water. The tests showed that 3D printing is accurate enough to produce prototype parts for optical systems. After testing, metal versions of 3D-printed parts could be ordered if desired to create imagers that would be more durable. Although the imager doesn’t provide the sensitivity of traditional hyperspectral imagers, the performance is sufficient for mapping terrain or detecting ocean colour in daylight. The researchers are now working to improve the sensitivity by making slightly larger versions of the instruments that would still be small and light enough for use on UAVs. “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.” 3D-printed budget imager Sensors The imager is light enough for small UAVs (Courtesy of João Fortuna, Norwegian University of Science and Technology)