HYPERSPECTRAL IMAGING


Hyperspectral image of stained glass. Spectra at points 1 and 2 show that the two blue tiles are made of different materials g


software suited to handling large amounts of spectral video data. Tis could change in the coming years, however, should demand for hyperspectral video rise. Jung expects the first firms to react will be those experienced in creating software for hyperspectral imaging, in addition to startups that emerge to address this demand. While the Ultris 20 provides excellent


spatial and spectral resolution, Jung remarked the micro-lens array of its light


Fantastic filters


Early last year, US firm Salvo Technologies acquired Ocean Insight’s Pixelteq optical filter line. As a result, it can now make its own linear variable filters, and is able to integrate them directly with off-the-shelf image sensors. ‘These filters cover


a different part of the spectrum as you move across it, with each row of pixels dedicated to a particular wavelength,’ explained Hugh Garvey, director of imaging at Salvo Technologies. ‘Our sensors can therefore be operated in a push broom mode, where either the camera or the subject


being imaged is moving – so each part of the subject can be imaged by each row of pixels – for example in airborne applications.’ He added that these


filters, which are complex to make and have only become available over the past few years, provide a very compact and cost-effective method for performing hyperspectral imaging. As customers understand more about these filters, however, they are demanding more spectral coverage in shorter filters, according to Garvey. There is therefore a push to make


these filters perform to a higher standard. ‘The resulting challenge, from a filter manufacturer’s point of view, is to try and get from one colour to another in as short a distance as possible – the slower the gradient is, the larger the image sensor required,’ he said. ‘We are improving our filter manufacturing technology so we can make a high- performance filter in as small a piece of glass as possible, which can then go on a smaller image sensor. This will lead to smaller hyperspectral imaging cameras.’


field technology does take up a considerable amount of space on the sensor, leaving fewer pixels for spatial resolution. He said larger detector arrays need to be made before the spectral and spatial resolution of this camera can be increased further.


Shrinking cameras An alternative approach to developing hyperspectral snapshot cameras is currently being taken in the Horizon 2020


project Multiple, which began at the end of last year and is being co-ordinated by the Aimen Technology Centre in O Porriño, Spain. Te three-year project was established with the aim of developing scalable monitoring solutions for different industrial processes using a range of photonic technologies, which, in addition to hyperspectral imaging, will include organic electronic sensors and laser-based spectroscopy. Te hyperspectral cameras under


development will cover the SWIR range – from 900nm to 1.7µm – and will be based on InGaAs detectors. Currently in the prototype stage, these detectors are equipped with linear filters. In the future they will be based on mosaic filters developed by Belgian research institute Imec. According to Dr Roi Mendez-Rial, a


research engineer at the Aimen Technology Centre and co-ordinator of the project, the mosaic filters will either be positioned directly on top of the InGaAs sensor using a hybrid integration approach, or integrated monolithically with the sensor. In order to make the new hyperspectral


technology fast and compact, each camera will be developed using a mosaic filter that includes only a specific set of spectral bands suited to the application it has been designed for – rather than covering a complete spectral range. One such intended application will be


in steel factories, where the cameras will be used to measure the temperature of the walls of furnaces independent of emissivity, as well as the temperature of moving steel slabs on production lines. Woodwork and food production are also key areas that the project partners are targeting, and so end


10 IMAGING AND MACHINE VISION EUROPE FEBRUARY/MARCH 2020 @imveurope | www.imveurope.com


Nireos


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