Linear variable filters — A camera system requirement analysis for hyperspectral imaging sensors onboard small Remotely Piloted Aircraft Systems

Improving the spectral detail of earth observation imaging from Remotely Piloted Aircraft Systems (RPAS) can greatly expand its potential for use in vegetation monitoring and specifically in precision agriculture. Spatially variable interference filters which can be placed very close to the image sensor offer an excellent opportunity for reducing the size, mass and complexity of hyperspectral imagers, allowing them to be mounted onboard small RPAS. Recent advances in filter deposition techniques allow to directly deposit interference filters on an image sensor. The monolithic integration of optical hyperspectral filters on top of a standard CMOS image sensor has been demonstrated by IMEC. Compared to the more conventional deposition of filters onto an external glass substrate, this new approach offers advantages in terms of cost, alignment accuracy, straylight, etc. A hyperspectral camera prototype compatible with small RPAS has been developed by VITO to demonstrate the potential of LVF-based compact spectral camera's. Whereas application of the filter technology offers major advantages for RPAS systems, it still faces some important challenges. The prototype system specifications need to fit a fixed wing RPAS platform that is able to cover several km
²
in a single flight with hyperspectral geo-information. It remains challenging to make a sufficiently compact camera system, achieve precise spectral band registration, handle the amount of data to be processed and cope with limited integration times possible during acquisition.