Designing observing strategies that take local conditions into account

A mixture of technologies needs to be considered when developing a strategy for methane emissions monitoring. Near-ground measurements, with sensors on aircrafts, drones, ground vehicles, or static locations, may be needed to identify emission sources and empower mitigation action.

Robust observation systems are needed to enable methane mitigation goals to be met. Spaceborne instruments are set to form the backbone of these global methane-monitoring observing systems thanks to their ability to detect large individual emission events and to assess regional emissions across large regions of the globe. 

New satellites, such as MethaneSAT and Tanager-1, expand the current set of monitoring instruments and offer high spatial resolution, providing greater opportunities to measure methane emissions, including in cloudy regions. Additionally, scheduling satellite observations during times of the year when environmental conditions are favourable would enhance data coverage, to the extent that that is feasible.  However, some regions will be more challenging to monitor than others due to environmental conditions – and relying on satellites alone may not be adequate for certain purposes in some regions.

To most effectively monitor methane emissions, a multi-tiered observing system is required. This is a system that uses different types of measurements to understand emissions as required by specific environmental conditions and user needs. This is analogous to a weather observing system, where satellite observations are combined with radar, ground station measurements and weather balloons to create the data needed for weather forecast models and long-term monitoring of climate trends. For instance, continuous monitoring by ground stations can measure air temperature in the arctic where satellite observations are limited. In contrast, satellites can infer air temperature over the ocean, where there are no ground-based stations. 

A universal design for a multi-tier observing system is unlikely to suit all scenarios due to diverse environments, methane source variability, and technology constraints. Local users will need to adapt measurement technologies to their specific conditions, needs, and resources. Where favourable observing conditions are rare, like in Ecuador or Indonesia, satellites will be less likely to effectively monitor large emissions events or inform validation of the methane emission inventories.  In these cases, robust systems will need to be developed to take up these tasks. Making such systems feasible with available resources, including in developing countries, is a critical task for researchers, policymakers, and donors.  

Alternative methane measurements technologies

A number of alternative technologies are being used to complement satellite methane monitors. These technologies are based on sensors mounted on aircraft, drones, ground vehicles or fixed locations. Used either individually or in combination, these systems offer a detailed view of methane emissions, filling in for the spatial and/or temporal scale that satellite systems are missing. Being near the source of the emissions, they can frequently detect much smaller emissions and help locate the specific source, helping guide mitigation. There is a rapid pace of research and investment to transform such individual technologies into robust monitoring systems and make such technologies more readily available. 

No single technology will be the silver bullet, able to effectively measure methane at all of the spatial and temporal scales required to support mitigation. Each technology gives only a partial view of the invisible methane world, and a combination of them, integrated in a multi-tier observing system, will be required. Moreover, all sensors can also be affected by environmental factors such as wind, cloud cover, and light availability. For instance, some passive ground-based sensors which rely on ambient light are similarly affected by low-light conditionsas satellite sensors are. In contrast, active sensors, which generate their own light source, remain unaffected by natural light conditions (as do some systems which do not utilize light absorption to detect methane). Further research is needed to assess how various alternative measurement approaches respond to environmental challenges. To develop an effective methane monitoring strategy, it is essential to understand the limitations of both satellite and alternative technologies.

As this report has shown, the exact mixture of technologies that will make up this system needs to be geographically specific, taking into account the emission characteristics and local environmental conditions. In some regions, satellite data alone may be adequate for regular monitoring of large emission events and top-down emission estimates. However, in other areas, additional technologies—potentially combined with satellite observations—will be required.

Looking beyond specific technologies

Building effective multi-tier observing systems entails much more than just deploying sensors: it requires coordinated efforts and support. With external support where appropriate, local stakeholders need to build the capacity to develop, evaluate, and adapt measurement technologies in their specific settings, and they need the resources to do so.

Practitioners in different regions facing similar challenges should be connected to exchange best practices and lessons learned, to allow user-led innovations to spread. And international efforts to develop testing protocols and facilities should be rapidly developed, to foster consistency and trust on produced data. 

To keep within its climate goals, the world needs to reduce fossil-related methane emissions by 75% by 2030.  Satellites will have a key role in this effort, monitoring the progress of well-understood mitigation steps but also highlighting new opportunities for action. With little time, knowledge must be shared freely and efficiently so that all stakeholders can maximise their impact in this collective fight.