A compact novel hyperspectral imager for more reliable and precise agriculture

Projections suggest that, without further action, the availability of water for irrigation will become a serious limiting factor to agricultural production and quality, particularly for growing cereals and potatoes. Many of the most productive regions of Great Britain at present, such as Kent and the East Anglia fens, are also where projections of both soil aridity and water scarcity are severe [1]. The Climate Change Risk Assessment Evidence report clearly specifies the need for a more coordinated action to achieve the ambitious reductions in water demand and to find solutions for future agriculture.

This research proposal is to address this particular issue by developing a novel concept of hyperspectral imager to remotely map the moisture content in crops and soil. At a time where scarcity of fresh water stocks is becoming an issue worldwide, the research will lead to an instrument offering precise feedback on the crop's water requirement and potential savings to farmers or communities. The proposed research will develop the next generation of space or airborne instrumentation for advanced sustainable agriculture, with a focus on strengthening resilience to environmental crises.

In the last decades, technological progress made in the field of Earth Observation instrumentation has revolutionised agriculture. Nowadays, hyperspectral technologies provide both valuable and essential information to modern agriculture by removing cost uncertainties from agricultural assets and by helping to prepare for and mitigate the effects of natural disasters. hyperspectral imaging techniques offer an accurate spatial and spectral snapshot of cultivated areas, helping in particular to monitor:

- water-stress, disease, insect attack, invasive species mapping and overall plant health

- seed sustainability, with remote measurement of the germination efficiency

hyperspectral instrumentation uses the spectral information in the image to reveal particular details about biology, mineralogy and chemical content, therefore providing valuable feedback regarding agriculture, earth science and environment.

Two novel instrumentation concepts will be developed and put together in this research to offer a step change in the hyperspectral capability, at the service of UK advanced sustainable agriculture. The first concept, capitalises on the use of an Integral Field Spectrometer integrating a slicer mirror (array of small thin slices of mirror) in a hyperspectral imager, and the second concept uses novel optical elements: Freeform gratings. Freeform surfaces are novel and revolutionary optical elements with no particular axis of rotation or symmetry. Traditionally, gratings are machined as flat or as lightly curved spherical surfaces because of limitations in the machining capability. Progress made in the field of ultra-precision machining can potentially enable the machining of complex, curved gratings to further improve the instrument compactness, image quality or modularity. Freeform optics are therefore promising components for space-based hyperspectral imagers for their ability to reduce the overall dimension, and therefore mass, of the satellite's payload, which is a critical parameter in space imaging systems.

[1] Committee on Climate Change, "Climate Change Risk Assessment evidence report - Synthesis report: priorities for the next five years." 2017.

The research proposal "A compact novel hyperspectral imager for more reliable and precise agriculture" is a multi-disciplinary project, which will endeavour to produce a reliable instrument using a novel optical element to meet agricultural requirements to maximise the academic, societal and economic impacts.

Freeform gratings are novel components and have great potential for commercial exploitation, maximizing both the economic and societal impact. This novel type of optical element will open up a wide range of applications in spectroscopy across diversion fields such as :

- Space: Freeform gratings are promising components for airborne or space-based hyperspectral imagers due to their ability to reduce the overall dimension, and therefore mass, of the satellite's payload, which is a critical parameter in space imaging systems.

- Bio-photonics and medicine: The substrate of the metallic freeform gratings can be machined into all sorts of shapes, making these components easy to miniaturize and incorporate into intricate optical systems.

- Food industry: Spectroscopy is an important tool in the food industry, providing quantitative and qualitative feedback on the food quality. Freeform gratings will have a key role to play in the next generation of spectrometers to analyse the chemical composition of food and drink.
As air- and space-borne hyperspectral imagery becomes cost-effective for precision farming and soil reclamation applications, better accuracy in assessing soil characteristics is needed for nutrients and amendment prescriptions, and irrigation management practices. This research offers the potential to map, from a remote platform the moisture level in soil and crops. At a time where scarcity of fresh water stocks is becoming an issue worldwide, the research will lead to an instrument offering precise feedback on the crops water requirements and potential savings to farmers or communities. Farmers will be the first beneficiaries ofthe technology developed in this research. The instrument will also provide feedback on crops monitoring such as measurement of disease, insect attacks, invasive species mapping and overall plant health.
The technology developed for this instrument can also find applications in space-based global measurement of greenhouse gases, such as atmospheric carbon dioxide (CO2), methane and helping keeping track of air pollution levels. Freeform grating could offer the accuracy, resolution, and coverage needed to characterize regional scale CO2 sources and sinks and quantify their variability over the seasonal cycle. Research work in this field will help the UK to keep a leading position in the design of space and remote sensing instrumentation.
The UK industry will also benefit from the research in this proposal with 2 potential commercialization outputs identified:

- The commercialization of the freeform gratings as a novel optical element and their integrations within high quality spectrometers (not necessarily hyperspectral imager).

- The commercialization of the digital data obtained from the airborne measurement and its distribution to the UK agricultural community.

The project will also measure a range of UK soil samples and help to quantity the moisture content from the spectrum. No such analysis specifically studying UK soils has so far been performed, and the proposed research will be highly relevant to a multitude of academic groups working on hyper spectral imaging.