Real-time high resolution visualisation of methane emissions from wetlands using multi-spectral infrared imaging

天然湿地是全球最大的强效温室气体甲烷排放源。在湿地的浸水土壤中产生了大量的气体，因为高地下水位阻止了大气中的氧气穿透土壤到任何显著的深度。在无氧条件下，腐烂非常缓慢，这就是为什么有机物质在许多湿地中以泥炭的形式积累。多年来，在测量湿地产生和排放的甲烷量方面投入了相当大的努力。某些类型的排放过程已被很好地理解，但其他类型的排放过程，特别是那些往往非常零星的排放过程，已被证明难以描述。甲烷是一种无色无味的气体，因此，目前所有测量其从湿地释放的方法都有一个偶然和猜测的因素，要么是放置小的室来捕获排放物，要么是放置更大的塔来测量湿地上方空气中的甲烷量。如果有可能“看到”从湿地释放的气体，这将极大地帮助我们了解触发泥炭土释放富含甲烷的气泡的过程，或者对植物作为管道从地表下释放甲烷的能力产生影响的过程。我们建议开发一种新技术来拍摄湿地甲烷释放的图像，这将涉及使用一种照相机，可以在人眼无法看到的热红外区域波长拍摄照片和视频。特殊的过滤器将用来去除大部分红外辐射，只留下两个小波段的波长：一个与甲烷相互作用，另一个穿过地球大气层。这两幅图像的不同之处将提供一幅清晰的红外辐射被甲烷吸收或释放的图像，这将允许富含甲烷的羽状物或气泡根据存在的甲烷量以人工颜色或灰色阴影进行成像。相机将在我们过去研究过的威尔士的几个湿地进行测试，这些湿地会根据季节和泥炭土壤的温暖和潮湿程度排放不同数量的甲烷。在不同的天气条件下，湿地的表面将在普通光和红外模式下成像，以确定当降雨系统进入一个地区时，通常会发生的大气压力下降，是否会引发泥炭中的气泡释放。我们还将研究阳光、风和湿度的变化如何影响甲烷通过某些水生植物多孔茎的运动。当我们用相机进行这些测量时，一个临时气象站将测量风速和风向、气温、阳光、湿度和气压。本研究收集的信息将为了解湿地的气体运动和释放如何受到外部因素的影响提供见解。这些信息将有助于改进现有的模型，这些模型试图模拟甲烷是如何从天然湿地产生和排放的，以及未来的气候变化如何影响天然湿地目前在向地球大气提供这种重要温室气体方面所起的作用。这项技术很可能引起其他研究甲烷排放的研究人员的兴趣，这些研究来自垃圾填埋场、湖泊和海洋、消化系统与驯养牛相似的野生动物，以及负责监测高度易燃气体可能构成安全风险的甲烷释放情况的机构。

Natural wetlands are the largest global emission source of the potent greenhouse gas methane. Copious amounts of the gas are produced in the waterlogged soils of wetlands because high water-table levels prevent atmospheric oxygen from penetrating the soil to any significant depth. Under oxygen-free conditions, decay is very slow, which is why organic matter accumulates as peat in many wetlands. Considerable effort has been invested over the years in measuring the amount of methane produced and emitted from wetlands. Certain types of emission processes are well understood but others, in particular the ones that tend to be very sporadic, have proven much more difficult to characterise. Methane is a colourless and odourless gas, and consequently all current methods to measure its release from wetlands involve an element of chance and guesswork in the placement of either small chambers to capture emissions or larger towers that measure the amount of methane in the air above a wetland. If it were possible to 'see' the gas during release from the wetland this could greatly help to improve our understanding of the processes that trigger release of methane-rich bubbles from peat soil or that have an effect on the ability of plants to act as conduits for methane from beneath the surface. We propose to develop a new technique to image methane release from wetlands which will involve using a camera that can take pictures and video at wavelengths in the thermal infrared region which cannot be seen with the human eye. Special filters will be used to remove most of the infrared radiation, leaving only two small bands of wavelengths: one that interacts with methane and a second that passes through the Earth's atmosphere unobstructed. The difference in the two images will give a clean picture of infrared radiation either being absorbed or released by methane, which will allow plumes or bubbles rich in methane to be imaged in artificial colours or as shades of grey depending upon the amount of methane present. The camera will be tested at several wetlands located in Wales that we have studied in the past, which are known to emit varying amount of methane depending upon season and how warm and wet conditions are in the peat soils. The surface of the wetlands will be imaged in both normal light and infrared modes under different weather conditions to determine whether a decrease in atmospheric pressure, which typically occurs when rain systems move into an area, can trigger release of gas bubbles trapped in the peat. We will also study how variations in sunlight, wind and humidity influence the movement of methane through the porous stems of certain types of aquatic plants. While we are making these measurements with the camera, a temporary weather station will be measuring wind speed and direction, air temperature, sunlight, humidity and air pressure. The information collected in this study will provide insights into how gas movement and release from wetlands are impacted by external factors. This information should be useful for improving current models that attempt to simulate how methane is produced and emitted from natural wetlands, and how future climate change might impact the role that natural wetlands presently play in supplying this important greenhouse gas to the Earth's atmosphere. The technique is very likely to be of interest to other researchers who study methane emissions from sources such as landfills, lakes and oceans, wild animals that have a digestive system similar to domesticated cattle, and agencies who are responsible for monitoring methane release in situations where the highly flammable gas could pose a safety risk.