A differential absorption LiDAR for multi-species greenhouse gas detection

迫切需要了解主要温室气体的迁移和大气浓度。我们正在开发一种激光设备，可以测量低层大气中温室气体的垂直分布，高度约为5公里，高度间隔约为50米。这将提供有关大气浓度变化的前所未有的信息，这些信息反过来又可用于推断这些温室气体的源和汇。气候科学家和政府监管机构将首次能够应对“如果你不测量它，你怎么能希望管理它”的挑战。卫星平台不能提供在低层大气中有用的高度分辨率，但这正是陆地-大气相互作用发生的地方，也是大多数重要信息所在的地方。其他地面遥感设备只提供列积分值，夜间不工作。我们的新型仪器在任何天气和任何时候都能工作。我们的新仪器使用一种称为DIAL（差分吸收激光雷达）的方法，其中激光以已知被一种温室气体吸收的波长发射到大气中。通过重复发射该波长的激光，但与不被任何其他温室气体吸收的激光波长交替，DIAL可用于测量温室气体的垂直分布。我们现有的激光雷达系统可以探测到约5公里的距离，我们的测试表明，在我们打算使用的采样频率下，我们用于温室气体探测的垂直分辨率约为50米。这项研究将为激光系统增加一个甲烷通道，并将其集成到我们基于望远镜的系统的激光组件和光学路径中。我们正在建造的仪器使用电信行业的组件，因此我们可以利用过去5年来在该行业发展的激光和电子技术的优势。使用早期技术的先前仪器价格昂贵（购买数百万英镑），而且又大又重，需要卡车来支撑，从而进一步限制了它们在远程地点的部署范围。我们的DIAL被设计成一个数量级，通过使用主要是现成的组件来构建，并且是现场便携式和眼睛安全的。

There is a compelling need to understand the transport and atmospheric concentrations of the main greenhouse gases. We are developing a laser-based device that can measure the vertical profile of greenhouse gases in the lower atmosphere to a height of about 5 km and at heights separated by about 50 m. This will give unprecedented information about the variability in atmospheric concentration that in turn can be used to infer the sources and sinks of those greenhouse gases. For the first time, climate scientists and government regulators will be able to address the challenge of 'how can you hope to manage something if you don't measure it'. Satellite platforms do not provide the height resolution to be useful in the lower atmosphere yet this is precisely where land-atmosphere interaction takes place and where most of the important information lies. Other ground-based remote sensing devices only provide column-integrated values and do not operate during the night. Our novel instrument will work in all weathers and at all times of the day. Our novel instrument uses a method known as DIAL (Differential Absorption Lidar) in which a laser is fired into the atmosphere at a wavelength that is known to be absorbed by one of the greenhouse gases. By repeatedly firing the laser at this wavelength but alternating with a laser wavelength that is not absorbed by any other greenhouse gas, DIAL can be used to measure the vertical profile of greenhouse gases. Our existing LiDAR system can range to a distance of about 5 km and our tests suggest that at the sampling frequency we intend to use, our vertical resolution for greenhouse gas detection will be about 50 m in the vertical. This research will add a methane channel to the laser system and be integrated into the laser assembly and optical pathway of our telescope-based system.The instrument we are building uses components from the telecommunications industry and thus we can take advantage of the miniaturisation in laser and electronics technology that has developed in that industry over the past 5 years. Previous instruments using earlier technology have been expensive (millions of pounds to purchase) and so large and heavy they require a truck to support them, thus further limiting their scope for deployment to remote locations. Our DIAL has been designed to be an order of magnitude less expensive to build by the use of mainly off-the-shelf components and to be field portable and eye-safe.