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

自然湿地是强有力的温室气体甲烷的全球最大排放源。大量的气体是在湿地被淹的土壤中产生的，因为较高的地下水位阻止了大气中的氧气渗透到土壤的任何重要深度。在无氧条件下，腐烂非常缓慢，这就是为什么有机物在许多湿地中以泥炭的形式积累。多年来，人们在测量湿地产生和排放的甲烷数量方面投入了大量的精力。人们很好地理解了某些类型的排放过程，但事实证明，其他类型的排放过程，特别是往往非常零星的排放过程，更难描述。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涉及到随机和猜测的因素，要么是放置小房间来捕获排放，要么是放置更大的塔来测量湿地上空空气中的甲烷数量。如果能够在从湿地释放的过程中“看到”气体，这将极大地帮助我们更好地理解泥炭土壤释放富含甲烷气泡的过程，或者影响植物作为从地表以下输送甲烷的管道的能力。我们建议开发一种新的技术来拍摄湿地甲烷释放的图像，这将包括使用一种相机，可以在人眼无法看到的热红外区域的波长上拍摄照片和视频。特殊的滤光片将被用来去除大部分红外辐射，只留下两个小波段：一个与甲烷相互作用，另一个畅通无阻地穿过地球大气层。这两张图像的不同之处将给出一张清晰的红外辐射被甲烷吸收或释放的图像，这将使富含甲烷的羽流或气泡被成像为人造颜色或灰色阴影，这取决于存在的甲烷数量。相机将在我们过去研究过的威尔士几个湿地进行测试，众所周知，这些湿地会根据季节以及泥炭土壤的温暖和潮湿条件而释放不同数量的甲烷。湿地表面将在不同天气条件下以正常光和红外模式进行成像，以确定大气压力的下降是否会触发泥炭中滞留的气泡的释放。大气压力下降通常发生在降雨系统进入某个区域时。我们还将研究阳光、风和湿度的变化如何影响甲烷在某些类型的水生植物多孔茎中的移动。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、日照、湿度和气压。这项研究收集的信息将为了解湿地的气体移动和释放如何受到外部因素的影响提供洞察力。这些信息应该有助于改进目前的模型，这些模型试图模拟甲烷是如何从自然湿地产生和排放的，以及未来的气候变化可能如何影响自然湿地目前在向地球大气供应这种重要的温室气体方面所起的作用。这项技术很可能会引起其他研究人员的兴趣，他们研究的甲烷排放来源包括垃圾填埋场、湖泊和海洋、消化系统类似于驯养牛的野生动物，以及负责监测高度易燃气体可能构成安全风险的情况下甲烷排放的机构。

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.