Methane-Detecting Satellites 101: The Completeness Quotient

Satellite “completeness” is a new and powerful concept in the push to slash climate pollution.

Satellites are growing in prominence as an important tool in addressing the climate crisis by spotting global emissions. There are already dozens of greenhouse gas-detecting satellites in orbit today, and both public and private institutions have announced plans to launch more in the future. Additionally, at COP27, the UN announced a new high-tech, satellite-based global methane detection initiative — The Methane Alert and Response System (MARS) — which will leverage satellite data to alert governments, companies, and operators about large methane sources to foster rapid mitigation.

As satellite constellations expand — along with the data and insights they provide — so does the nuance in how they are used. To match the right tool with the right job, it’s important to understand what each satellite is designed to do, and how their data can help decision makers meet diverse but interrelated climate goals and objectives.

For this reason, RMI’s new report and Satellite Point source Emissions Completeness Tool (SPECT) aim to help users understand and assess satellite “completeness” as it relates to identifying and tracking super-emitters of methane, a greenhouse gas (GHG) 85 times more potent than CO₂ on a 20-year time frame. Here, we unpack the definition, context, and importance of satellite completeness as a new and powerful tool in the push to slash climate pollution.

Satellites Make Invisible Emissions Visible

A “space race to save climate” is under way, and for good reason. Alarming, record-setting years for atmospheric concentrations of carbon dioxide and methane call for immediate and widespread mitigation. You can’t manage what you don’t measure, and making the previously invisible emissions visible from space is critical to halving carbon emissions by 2030 as pledged in the Paris Agreement, and to meeting the Global Methane Pledge’s target to cut methane emissions 30 percent by 2030.

Understanding Different Satellite Capabilities

Different satellites are designed to monitor different things in different ways (an article in Geospatial World dives deep into this very topic). The European Space Agency’s TROPOMI, for example, can map methane, nitrogen oxides, carbon monoxide, and various aerosols as it passes daily over Europe, Asia, Africa, and the Americas — a significant geographic reach. Its resolution can narrow down to a couple square miles of Earth. Compare that with the GHGSat-C1 satellite, which is designed to provide high-resolution monitoring of industrial facilities down to the point-source level (such as specific oil and gas compressor stations or pipelines) at 25-meter scale. Or compare those with EDF’s MethaneSat, which sits somewhere between the two, providing global, high-resolution coverage of methane emissions regionally as well as down to the level of oil and gas facilities.

Each of these has its use case: A satellite like TROPOMI can be effectively used to “true up” a regional or national reported GHG inventory, while a satellite like GHGSat can be used to alert an oil and gas operator to a leak at one of its facilities so that it can be fixed immediately.

Pinpointing Super-Emitters

While regional-, sector-, and asset-level data enabled by satellite observations are all important, the time-bound urgency of the climate crisis led RMI to focus on the need to pinpoint methane super-emitters. Super-emitters are large point sources of methane that emit at high rates, typically 25 kilograms of methane per hour or more. Super-emitting sources can include leaking oil and gas production equipment, venting coal mines, or landfills and waste sites.

Such sources have historically proven difficult to track, yet they represent our biggest near-term opportunity to mitigate methane given their disproportionate impact and the fact that many — once identified — can be addressed quickly and cost-effectively. And new satellites with distinct capabilities are changing the game.

Defining Completeness and Understanding Its Components

A new metric of satellite completeness can help decision makers better understand the strengths and limitations of various satellite technologies — specifically in their ability to pinpoint methane super-emitters.

Completeness combines three satellite parameters in one metric to quantify the share of global methane point source emissions that can be detected:

• Detection sensitivity, or the emissions threshold that can be detected by the satellite instrument (usually described as an emissions rate of methane mass or volume under certain conditions)
• Spatial coverage, which is the overall geographic area covered by the satellite
• Sampling frequency, or how often a satellite successfully completes an observation of a given area

Current satellite discussions tend to focus solely on detection limits and pay little attention to the other system attributes — or treat these attributes as independent of one another. When taken together, however, these parameters provide better comparability for the task of detecting super-emitters.

Applying Completeness to Decision-Making

Among other benefits, the completeness metric can help operators identify which instruments offer the best prospects of tackling leak detection, guide regulators in designing and implementing methane monitoring programs, and boost understanding among civil society when comparing satellites to other measurement technologies.

To understand how different technologies stack up according to the metric of completeness, we encourage you to visit SPECT.

More to Come

Methane point sources are incredibly complex, to say nothing of greenhouse gas emissions more broadly. While the completeness metric is valuable for this use case, we hope to build upon this work by addressing additional use cases and broadening awareness of how various technologies can be used to improve global climate intelligence. By making emissions sources more visible, increasing data accessibility, and acting to mitigate those emissions, we can achieve rapid progress in this decisive decade for our climate.