Drone-Assisted Fourier-Transform Spectroscopy for Fugitive Emission Sensing

该项目是光子学（Reid，Heriot-Watt大学）和机器人学（Ramamoorthy，爱丁堡大学）研究人员之间的联合提案。这是一个跨学科的合作，这是必要的，以便以一种新的和令人兴奋的方式解决甲烷和挥发性碳氢化合物从炼油厂，石油化工厂，碳捕获和储存设施和垃圾填埋场等设施的无组织排放问题。这些排放量每年给能源部门造成高达50亿美元的损失，占温室气体排放量的12%，并危及工人安全和公众健康。我们的想法是使用中红外激光，通过寻找特定于单个化学物种的波长的特征反射来感知碳氢化合物的存在。这种“气体吸收光谱”远非新的，但我们将以与传统方法完全不同的方式实现它。通常情况下，光学气体检测的工作原理是通过气体传输单波长并寻找强度变化。对于散逸性排放传感，这是使用一种称为DIAL的技术来实现的，该技术向空气中照射一束强烈的光束，并检测来自空气中颗粒的弱后向散射（米氏散射）。通过寻找两个间隔很近的波长之间反向散射强度的微小差异，DIAL可以检测到一种（也只有一种）化学物质的存在。它的主要缺点是返回光的弱点（毕竟，空气是一个非常差的反射器！）傅里叶变换光谱学（FTS）是实验室化学鉴定的黄金标准，它使用一个类似于灯丝灯泡的光源，一次性探测大量波长范围内的反射。遗憾的是，这种热光源的光束质量非常差，因此不能在适合环境感测的长距离上传输。2004年，Heriot-Watt证明宽带激光可以用于FTS，将热源的波长覆盖范围与激光的光束质量相结合。这是在环境感测中所需的长路径长度上实现FTS的游戏规则改变者，但是（由于信噪比的原因）与返回光非常弱的几何形状不兼容。无人机（UAV或drone）技术现在已经达到了成熟的水平，我们可以设想在UAV上飞行后向反射器，以提供将激光返回到地面探测器的高效手段。这个概念，我们称之为Drone-Assisted FTS（DRAFTS），立即提供了优于当前最先进技术的改进功能，包括：1。通过使用宽带中红外光，获取多种化学品的浓度和通量图，并允许建立相关性和推断因果效应。2.由于安装在无人机上的后向反射器消除了对空气中颗粒物的依赖，并且效率提高了10，000倍，因此可以在更大的范围内和不同的大气条件下进行传感。3.在更广泛的场景中部署，利用固态激光器的紧凑性，例如，使用由无人机跟踪的移动激光源来测量道路或管道沿着的排放。（逃逸排放传感领域的领导者）和Chromacity（飞秒激光器制造商）-我们的目标是评估草案，并发展到一个水平，我们可以证明其在模拟逃逸排放现场试验的效用。我们的合作伙伴为该项目贡献了8.5万英镑，并跨越了从制造商到最终用户的供应链，从而为DRAFTS概念的早期商业化提供了关键机会。

This project is a joint proposal between researchers in Photonics (Reid, Heriot-Watt University) and Robotics (Ramamoorthy, University of Edinburgh). It is a cross-disciplinary collaboration, which is necessary in order to tackle in a new and exciting way the problem of fugitive emissions of methane and volatile hydrocarbons from installations such as refineries, petrochemical plants, carbon-capture and storage facilities and landfill sites. These emissions cost the energy sector up to $5B per year, account for 12% of greenhouse gas emissions and jeopardise worker safety and public health. Our idea uses mid-infrared laser light to sense the presence of hydrocarbons by looking for characteristic absorptions at wavelengths specific to individual chemical species. Such "gas absorption spectroscopy" is far from new, but we will implement it in a radically different way to conventional approaches. Normally, optical gas detection works by transmitting a single-wavelength through a gas and looking for an intensity change. For fugitive emissions sensing, this is implemented using a technique called DIAL, which shines an intense beam into the air and detects the weak backscattering of this light from particles in the air (Mie scattering). By looking for small differences in the backscattered intensity between two closely-spaced wavelengths, DIAL can sense the presence of one (and only one) chemical species. Its main drawbacks are the weakness of the returned light (after all, air is a very poor reflector!) and its sensitivity only to one chemical species in any given set-up.The gold standard for lab-based chemical identification is Fourier-transform spectroscopy (FTS), which uses a source similar to a filament light-bulb to explore absorptions over a massive wavelength range all at once. Sadly, such thermal light sources have very poor beam quality, so cannot be transmitted over the long distances appropriate to environmental sensing. In 2004, Heriot-Watt demonstrated that broadband laser light could be used for FTS, combining the wavelength coverage of a thermal source with the beam quality of a laser. This is a game changer for implementing FTS over a long path length as required in environmental sensing, but (for reasons of signal-to-noise) is incompatible with a geometry in which the returned light is very weak. Unmanned aerial vehicle (UAV, or drone) technology has now reached a level of maturity that we can conceive of flying a retroreflector on a UAV to provide a highly efficient means of returning the laser light to a ground-based detector. This concept, which we call DRone-Assisted FTS (DRAFTS), immediately offers improved capabilities over the current state-of-the-art including: 1. Acquisition of concentration and flux maps of multiple chemicals, enabled by using broadband mid-infrared light and allowing correlations to be established and causal effects to be inferred.2. Sensing with greater range and in diverse atmospheric conditions, since the UAV-mounted retroreflector eliminates the reliance on airborne particles and offers 10,000 times greater efficiency.3. Deployment in a wider range of scenarios, exploiting the compactness of solid-state lasers, such as using a travelling laser source tracked by the UAV to survey emissions along a road or pipeline.Working with two key partners -- NPL (a leader in fugitive emissions sensing) and Chromacity (a femtosecond laser manufacturer) -- we aim to evaluate DRAFTS and develop it to a level where we can prove its utility in a simulated fugitive emissions field trial. Our partners are contributing £85K toward the project, and span the supply chain from manufacturer to end-user, thus providing critical opportunities for early commercialization of the DRAFTS concept.