CHAFF is a Surrey-designed and built hyperspectral imager prototype intended for the 6U CubeSat platform. Capable of taking hyperspectral images across the wavelength range 460 nm – 820 nm at a best spectral resolution of 3.46 nm (at 546 nm), CHAFF has been designed holistically: consideration of the operational constraints of the CubeSat platform since design inception has allowed the development of techniques which address these constraints within the optical design. For example, CHAFF will employ optically aided image co-registration in order to deal with the physical pointing instability of the CubeSat and co-register the band images on-board the satellite. This will in turn improve the performance of image compression algorithms, which rely on spatial, spectral and statistical redundancy within the hypercube to achieve optimal performance. Additionally, CHAFF has been constructed with commercial off-the-shelf optics, to keep the design commensurate with a university CubeSat budget. Presented here is an update of the progress achieved, focusing on data collected by CHAFF during a field trial undertaken to assess the abilities of the instrument. Performance of the image co-registration and the instrument calibration on natural scene data is assessed, and the behavior of the instrument when presented with vegetation targets is analysed.
CubeSats are currently gaining significant traction in Earth Observation, with increasingly advanced instrumentation such as hyperspectral imaging. However, the challenges of bringing such instrumentation to CubeSats are great; the platform suffers from severe physical, operational and budgetary constraints. Adopting a holistic design methodology may hold the key to allowing science-grade Earth Observation to be achieved from a CubeSat. Presented here is CHAFF (CubeSat Hyperspectral Application For Farming), a low-cost hyperspectral imager prototype, capable of taking 1024 spectral bands between 460 nm - 820 nm. CHAFF has been constructed using commercial off-the-shelf optics, in order to produce a design commensurate with the typical resources of a university CubeSat mission. CHAFF has been calibrated at the National Physical Laboratory, in order to assess the performance of the COTS optics. An impressive spectral resolution of 3.46 nm at 546 nm has been achieved, and 74.95% of CHAFF's pixels exhibit a linearity deviation of < 2%.
Presented here is CHAFF (CubeSat Hyperspectral Application For Farming), a design concept for a CubeSat-based Hyperspectral Imager (CHSI) intended to supply high quality hyperspectral image data cubes to the agricultural community. CHAFF has been designed holistically as a system, considering all design and operational characteristics of a CHSI instrument and platform together: including the re-stricted payload mass and volume associated with CubeSats, the platform pointing stability/accuracy limitations, and the restricted downlink data budget. To this end, CHAFF will employ optically aided geometric co-registration methods, which will allow on-board construction of the hyperspectral data cube. This allows the use of powerful lossless data compression schemes to mitigate the downlink data budget limitations. In addition, a calibration methodology using a tuneable laser source at NPL, will be employed pre-flight to achieve rapid and accurate spectral and radiometric calibration, essential for the production of science-grade data sets from the proposed CubeSat constellations. A benchtop prototype has been constructed and a promising spectral resolution of 3nm at around 625nm has been achieved. In addition the auxiliary imager for the optically-aided geometric co-registration has been demonstrated.