Until now, hyperspectral remote sensing was only possible with large, complex and expensive systems, according to the Fraunhofer IST in Braunschweig. This is where the ESA-funded Rainbow project comes in. Together with Airbus Defense & Space, Vista Geowissenschaftliche Fernerkundung GmbH and the Fraunhofer Institute for Applied Optics and Precision Engineering IOF, the Fraunhofer IST has created a new generation of compact hyperspectral sensors for small satellites.
From the filter directly onto the chip
At the center of the development is a bandpass filter based on filter-on-chip technology, which was manufactured at the Fraunhofer IST and covers over 30 spectral channels in the range from 400 to 1700 nm. Three linearly variable bandpass filters were combined on a 10 × 10 mm² glass substrate. In order to realize the spectral variation and separate the filter areas, IST used microstructuring processes such as photolithography and lift-off processes. The result is a compact, robust and economical component that is suitable for use on small satellites and enables hyperspectral measurements.
The filters manufactured at the IST are based on high-precision sputtering processes such as those used on the institute's own EOSS/Opta-X sputtering platform. This technology enables both linearly variable filters with a large spectral bandwidth and pixel-precise structured filter stacks that can be integrated in front of the detector. This eliminates the need for complex optical setups. The size, weight and costs of the instruments are reduced - an advantage for applications in space, but also for mobile or industrial systems. "With Rainbow, we at the Fraunhofer IST have taken a decisive step towards making high-precision hyperspectral data economically available on small satellites for the first time," says Dr. Philipp Farr, Group Manager Precision Optical Layers at the Fraunhofer IST.
Hyperspectral data as the basis for precise decisions
This means progress for agriculture. The hyperspectral data that can be obtained with Rainbow allows a more detailed analysis of plant conditions, for example with regard to nutrient supply, stress factors or water content. This enables precise conclusions to be drawn. New perspectives are also opening up in quality and yield forecasting, for example through the satellite-based assessment of protein or nutrient content. In addition, the data can be used to determine the carbon content of soils and thus make certification processes in the area of carbon sequestration more efficient.
With the completion of the filter module, the Fraunhofer IST has concluded its contribution to the Rainbow project. The developed and qualified filter components now form the basis for further integration into the overall optical system and for subsequent validation and test campaigns in the project.