There is therefore a need to reconcile and validate bottom-up emission inventory estimates and process-based models with top-down (measurement based) methodology. Bottom-up estimates of the global methane budget (750 Tg yr −) are approximately 30% larger than equivalent top-down estimates (600 Tg yr −). Bottom-up inventories combine data-driven emission factors with statistical activity data, or use process-based modelling, whereas top-down methods combine atmospheric sampling with atmospheric advection (or dispersion) models to derive emission fluxes. Emission flux quantification generally relies on either bottom-up, or top-down, methodologies, and validation of inventories requires a comparison of both approaches. Quantification of methane emissions at local scales (defined for the purposes of this review to be less than 1 km) is important for understanding natural methane production and emission processes, and also for informing emission reduction strategies and regulation for anthropogenic methane sources. Both emissions of CH 4 to atmosphere and the absolute concentration of CH 4 in the atmosphere have increased over the past decade, and there are concerns that climate feedbacks are further increasing emissions from natural sources. Understanding and quantifying the global methane (CH 4) budget is crucial for the prediction and mitigation of future climate change. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'. This paper aims to provide an overview of currently available UAV-based technologies and sampling methodologies which can be used to quantify methane emission fluxes at local scales. Developments in the models used to simulate atmospheric transport and dispersion across small, local scales are also crucial to improved flux accuracy and precision. Their use is not without challenge, however: further miniaturization of high-performance methane instrumentation is needed to fully use the benefits UAVs afford. UAVs can be uniquely equipped to monitor natural and anthropogenic emissions at local scales, displaying clear advantages in versatility and manoeuvrability relative to other platforms.
The advancements in unmanned aerial vehicle (UAV) technology over the past decade have opened up a new avenue for methane emission quantification. There are ongoing international efforts to constrain the global methane budget, using a wide variety of measurement platforms across a range of spatial and temporal scales. Understanding and quantifying the sources (and sinks) of atmospheric methane is integral for climate change mitigation and emission reduction strategies, such as those outlined in the 2015 UN Paris Agreement on Climate Change. Methane is an important greenhouse gas, emissions of which have vital consequences for global climate change.
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