Advances and challenges in quantification of greenhouse gas emissions by UAVs – A review

Accurate and efficient quantification of emissions from sources (both natural and anthropogenic) underpins our understanding of the natural drivers of climate change and the success of emissions mitigation strategies. While there exists many excellent methods and measurement networks from which to constrain emissions at national and regional scales (e.g. through transport inversion modelling), a dynamic and accurate picture of emissions from hotspot sources (e.g. landfill, oil and gas infrastructure etc) remains a technical and scientific challenge. Recent international agreements and national regulations to monitor, report, and validate GHG emissions by sector, all require robust and standardised approaches to directly measure emissions to prioritise targets for emissions reduction and mitigation.

Emissions quantification by UAV survey is a rapidly expanding field both academically and commercially. Since the first known report on the feasibility of such a capability around 10 years ago (2014), there now exists a mature international academic community, which continues to refine and validate methods, and a growing international commercial sector that can now provide survey capability and drive further technological development. However, transparency and robust validation of methods remains a barrier to largescale adoption by regulators and those compiling national emissions inventories.

This paper will review recent advances in unmanned aerial vehicle (UAV) platforms, GHG instrumentation, methodologies and field operations in the pursuit of emissions quantification. Building on Shaw et al., 2021 (https://doi.org/10.1098/rsta.2020.0450), which reviewed methane emissions quantification by UAVs at that time, we report and reflect here on current progress, capability, and challenges. We will report recent fieldwork (by ourselves and published by others)  to quantify methane emissions from natural and anthropogenic sources and discuss promising new combined survey approaches that could help bridge the gap between snapshot emissions case studies and more long-term (dynamic) monitoring. We shall also discuss future work planned to survey onshore UK anthropogenic sources by the UK NERC MOMENTUM project.