Iliya Shofman, University of Toronto
Adyn Myles, University of Toronto
Abeer Fatima, University of Toronto
Shiqi Xu, University of Toronto
Iliya Shofman, Mr. , University of Toronto
Crop residue is an important metric used for agricultural land-use monitoring and climate science research. While most of the crop residue studies use visible (VIS) and near infra-red (NIR) hyperspectral imagery, there has been a lack of data available in the short-wave infra-red (SWIR) range which would allow scientists to make clearer distinctions between the types of ground vegetation and its water saturation level. While this information is critical for emerging smart agriculture practices and for carbon sequestration analyses, there is a clear gap in the available data and remote sensing capabilities for SWIR imagery of agricultural land in rural Canada.
The University of Toronto Aerospace Team is developing “FINCH EYE”, an optical payload for a 3U+ CubeSat to be launched in Q4 2027 that will gather crop residue data across Canada. With only 1.5U (10x10x15cm) of volume and <0.5kg of mass allocated to the hyperspectral imaging payload, a number of challenges arise with the optical design. A novel push-broom architecture with a GRISM dispersive element was chosen to keep the design compact and avoid folding the light path. A GRISM is a cemented prism-grating-prism sandwich device that disperses light without bending the overall ray path. This is advantageous as it enables an in-line optical assembly, which is much simpler to fabricate and is less prone to misalignment. To the authors’ best knowledge, the FINCH EYE may be the first hyperspectral imaging payload with a GRISM design to be demonstrated for such a compact form factor. The FINCH EYE will be capable of collecting hyperspectral data from 900nm to 1700nm at <8nm spectral resolution, with a spatial resolution of 100m, swath width of 10km, and signal-to-noise ratio (SNR) of >30. A preliminary feasibility analysis determined that these performance specifications can be achieved within the tight mass and volume constraints while still yielding scientifically valuable data.
In this paper, we seek to describe the optical design process of FINCH EYE, which leverages a combination of commercially available off-the-shelf (COTS) optics and custom components. The selection process for each component is detailed, with particular attention given towards ensuring reliability in the outer space operating environment. The optical and optomechanical design will be presented, with optical ray-tracing, tolerancing, stray-light, and thermal analyses performed in commercial software such as Ansys ZEMAX OpticStudio. Radiometric analysis, modelling the impact of atmospheric scattering and absorption using MODTRAN is also presented, validating the SNR. A structural-thermal-optical performance (STOP) analysis is currently being performed in Sigmadyne SigFit in order to accurately analyze the impact of thermoelastic deformations of the optomechanical housing on the optical performance of the payload.
An optical breadboard demonstrator prototype is currently under development, and we may share experimental procedures for aligning and calibrating the hyperspectral imager. The photon detection efficiency of the SWIR camera using an InGaAs detector will be characterized during a separate measurement. Several functional tests that facilitate validating the data processing algorithms will be described as well. While we await the fabrication of some custom mechanical components, plans for alignment and integration of the final payload will also be presented.