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FLying ultrA-broadband single-shot InfraRed sensor

Periodic Reporting for period 1 - FLAIR (FLying ultrA-broadband single-shot InfraRed sensor)

Reporting period: 2016-11-01 to 2018-04-30

The FLAIR project seeks to address known challenges in the context of the significant effort that is observed nowadays in active air quality improvement. In order to be successful, these measures need be complemented by air quality monitoring at large scale to ensure compliance with air quality legislation but also to provide information for political decision making regarding air quality and safety. Large spatial coverage is particularly problematic outside the dense urban network of air quality monitoring stations. FLAIR proposes to close this gap. The overarching objective of the project is the development of a compact, cost effective and high-performance air sampling sensor based on cutting-edge photonic technology, capable of performing high-specificity and high-sensitivity sensing over large areas as a result of its installation aboard a drone. Directly targeted applications include air quality monitoring around industrial infrastructures, maritime and land based traffic, landfills and agriculture facilities. The sensor can also be used to coordinate emergency service response in the case of catastrophic events like wildfires, volcanic eruptions or chemical accidents. Operating in two separate infrared atmospheric windows, the FLAIR sensor can detect minute traces of molecules in complex gas mixtures from their characteristic infrared absorption fingerprints and provide real time information to the operator of the drone. Making the sensor airborne through its integration aboard a drone brings a clear advantage regarding system deployment and pervasive sensing over large areas. Additionally, due to the local character of its sensing operation, the FLAIR sensor can also provide data from inside optically dense clouds and plumes, which are usually not accessible by ground-based laser remote sensing methods.
As a first step, the Consortium defined the main functional requirements for the FLAIR sensor and the drone system. These are important to understand the capabilities that the sensor must present and the limitations of its airborne operation. Based on the expected sensitivity of the FLAIR sensor, a list of target gases of interest for the project and corresponding concentrations in the atmosphere was compiled. Following this initial accomplishment, the preliminary architecture for the sensor was established, including specifications for each of its subsystems as, for example, the laser source, the gas cell where the laser beam is reflected multiples times to emulate a longer beam path through the gaseous mixture, the spectrometer with the optical elements and the infrared camera detector. The image provided by the latter contains information about the gaseous mixture, as the pattern of absorption of infrared light that is observed can be used to identify specific molecules, based on the known characteristics of each species. Extensive laboratory spectroscopy tests have been performed in order to identify the most important input parameters for the sensor design. Additionally, a reference database, containing information about the absorption characteristics of the relevant species has been established and will be crucial for the validation phase of the project. Regarding sensor's subsystems, significant progress has been achieved in the development of the two laser sources operating in the two separate infrared windows, specially regarding their miniaturisation requirements for drone integration; the infrared camera prototype has already been designed, assembled, tested and delivered for integration in the final sensor; as for the gas cell, several prototypes have been tested and the Consortium is striving to optimise its final footprint without compromising the stability of the device and the delicate alignment of its optical elements; a preliminary version of the 2D spectrometer has been designed and first experimental results have shown margin for improvement as subsystem development matures. In sum, at this stage of the project, the development of every constituent of the FLAIR sensor is well underway and the Consortium is confident it will be able to integrate it and interface it correctly with the drone and reach the desired performance levels.
The progress beyond state-of-the art that the project is targeting covers the sensor as a whole, at system level, and its subsystems as well. The FLAIR solution, when compared with existing non-laser sensing systems for air quality monitoring, presents an encouraging compromise between cost effectiveness, performance and footprint. Although the targeted selectivity and sensitivity are not as high as those that can be obtained with mass spectrometry methods, these are limited by their footprint and complexity. Electronic noses, on the other hand, are commercially available at reasonable prices but suffer from low accuracy, resolution and selectivity. Fourier Transform InfraRed Spectrometers are able to combine cost-effectiveness with high resolution but include moving mechanisms, which require precise alignment and are not suited for drone operation. Several systems based on light sources operating in the infrared range have enabled highly sensitive and selective detection of molecules. However, those solutions typically remain confined to research laboratories due to their narrow spectral operating window (covering only very few molecules), their complexity and prohibitively high cost. FLAIR sets to provide equivalent performance using a multipass cell, simultaneous detection of multiple species in a single shot measurement and a small footprint at a fraction of the cost. The integration of the FLAIR sensor aboard a drone will enable cost-effective operation and large area coverage for pervasive air quality monitoring.

At the subsystem level, progress beyond state-of-the-art has already been reached, attributable to the infrared camera, which features at its core a focal plane array of VPD PbSe, constituting the first uncooled medium wave infrared detector monolithically integrated with its read out Si-CMOS integrated circuit of the market. The detector is sensitive in a wide spectral band, resilient to in-flight vibrations, humidity and includes passive heat dissipation elements in its packaging.

Progress with respect to current state-of-the-art for other subsystems such as the multipass cell, the laser source and the imaging optics is expected to be achieved in the second half of the project and the current stage of activities shows promising results towards that direction.

Even though it is still too early to assess achievement of the expected impacts of the project, halfway through its lifetime, the Consortium is confident that it will be able to deliver a highly innovative instrument representing a breakthrough in broadband infrared spectroscopy with unprecedented performance and cost-effectiveness for better and pervasive environmental sensing, contributing towards securing and reinforcing industrial European leadership in sensing applications. The modular design of the instrument will enable the creation of a number of different end products, where optimisation can be made with respect to different applications, resulting in a technical and commercial flexibility that allows tackling various issues in which trace gas detection is key.