Bavo Delaure

NOVEL HYPERSPECTRAL IMAGER FOR LIGHTWEIGHT UAVS

VTT Technical Research Centre of Finland has developed a new miniaturized staring hyperspectral imager with a weight of 350 g making the system compatible with lightweight UAS platforms. The instrument is able to record 2D spatial images at the selected wavelength bands simultaneously. The concept of the hyperspectral imager has been published in the SPIE Proc. 74741. The operational wavelength range of the imager can be tuned in the range 400 - 1100 nm and spectral resolution is in the range 5 - 10 nm @ FWHM. Presently the spatial resolution is 480 × 750 pixels but it can be increased simply by changing the image sensor. The field of view of the system is 20 × 30 degrees and ground pixel size at 100 m flying altitude is around 7.5 cm. The system contains batteries, image acquisition control system and memory for the image data. It can operate autonomously recording hyperspectral data cubes continuously or controlled by the autopilot system of the UAS. The new hyperspectral imager prototype was first tried in co-operation with the Flemish Institute for Technological Research (VITO) on their UAS helicopter. The instrument was configured for the spectral range 500 - 900 nm selected for the vegetation and natural water monitoring applications. The design of the UAS hyperspectral imager and its characterization results together with the analysis of the spectral data from first test flights will be presented.

Spatially variable filters — Expanding the spectral dimension of compact cameras for remotely piloted aircraft systems

Recent advances in hyperspectral imaging techniques using spectral filters deposited directly onto an image sensor chip, and suitable for RPAS platforms, are reported in this paper. New filter configurations for a compact spectral camera are described and a prototype of the compact hyperspectral payload developed for small RPAS systems, as well as the first data acquired with the new camera are presented. The spectral range of the payload was optimized for earth observations such as vegetation monitoring or water quality studies. Although the spatially variable filters have to date only been used in small satellite sensors, this technology has a clear potential for RPAS platforms.

Radiometric calibration of the cosi hyperspectral RPAS camera

The COSI hyperspectral imaging system, suitable for small RPAS, is able to produce high resolution hyperspectral data products. By extensive inflight testing, we have identified the main challenges for achieving reliable high quality results. Based on these insights, we propose a refined radiometric calibration strategy. It uses a set of three reference targets, two grey and one colored target, which are to be measured inflight. We present on-ground measurements of the targets with COSI, as in flight measurements, demonstrating the merits of the approach are still ongoing.

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 cameras. 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 km2 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.