Methane has been known for decades as the "silent accelerator" of climate change. Although it remains in the atmosphere for a significantly shorter time than carbon dioxide, its heat-trapping ability is many times greater. Over a period of one hundred years, methane warms the planet approximately 28 times more powerfully than CO₂, and in the first twenty years after release, even about 80 times more powerfully. That is precisely why this gas has become the focus of new international promises, such as the Global Methane Pledge initiative, in which governments and industry commit to reducing anthropogenic methane emissions by about 30% by 2030.

One of the large, yet often neglected sources of methane are municipal waste landfills. Estimates show that landfills account for more than ten percent of total human-caused methane emissions. At a time when every additional ton of greenhouse gases makes a difference, the focus of scientists and regulators is rapidly shifting from the energy sector and fossil fuels towards waste – a place where methane is released slowly, diffusely, and often far from the public spotlight.

In the last few years, satellites have become a key tool for revealing these "invisible" emissions. They first established themselves in monitoring methane leaks from oil and gas fields, pipelines, and facilities. Today, the same technology, enhanced by better spatial resolution and sophisticated algorithms, is moving to a new area – waste landfills, where the picture of emissions is far more complex, but the potential for reduction is also great.

Study over Madrid: how satellites look for methane leaks from landfills

On December 15, 2025, the European Space Agency (ESA) published a detailed account of a pioneering project over the Las Dehesas landfill, which is part of the Valdemingómez Technology Park southeast of Madrid. It is a large municipal landfill approximately 18 kilometers from the center of the Spanish capital, where a significant amount of landfill gas is generated – a mixture of methane, carbon dioxide, and other compounds.

The aim of the study is to test whether a combination of satellite, aerial, and ground measurements can provide a sufficiently detailed picture of emissions from the landfill to show operators exactly where gas is escaping from the collection system. Instead of general emission estimates based on models or the amount of waste deposited, experts are trying to gain an almost forensic insight into the behavior of methane over every hill and every surface of the landfill body.

Since the spring of 2025, a team bringing together researchers from the University of Leicester, ESA experts, the Canadian company GHGSat, the Netherlands Institute for Space Research SRON, the International Methane Emissions Observatory (IMEO) under the United Nations Environment Programme, and other partners, has been conducting a series of coordinated measurement campaigns over Las Dehesas. On the ground, gas concentrations are measured, drones and aircraft with special sensors fly directly above the landfill, and satellites provide a broader and repeatable view from orbit.

By combining these levels of data, scientists obtain what they themselves call an "unprecedented level of insight". They can track how emissions change over time, how they react to maintenance work, changes in the disposal schedule, and even meteorological conditions such as wind or sudden temperature changes. For the landfill operator, this means they no longer have to guess where the problem originates – but can see it, quantify it, and, most importantly, quickly rectify it.

From a global picture to leaks the size of a few kilograms per hour

The foundation of the new methodology is a combination of two groups of instruments. The first group is represented by missions that provide a global picture, such as the Sentinel-5P satellite from the Copernicus program. Its TROPOMI instrument flies over the entire planet every day and measures methane concentrations over large areas, with a spatial resolution of the order of several kilometers. These data allow for the creation of "hotspot" maps of methane where it is clearly visible that an elevated concentration is present over a certain city, industrial zone, or landfill.

Based on such a global map, the online tool Methane Hotspot Explorer operates, which within the Copernicus Atmosphere Monitoring Service (CAMS) displays gaseous methane "plumes" associated with so-called super-emitters. Machine learning in the background of the system analyzes new satellite scenes every week, looks for patterns characteristic of leaks, and marks the locations of potential sources. Although these data do not have centimeter precision, they are crucial for discovering where to look for a more detailed answer.

The second pillar of the new generation of monitoring consists of commercial and research satellites with very high spatial resolution, such as those developed by GHGSat and other operators. Their instruments, such as the sensor with a resolution of about 25 x 25 meters used in Madrid, can detect individual methane plumes over relatively small objects – a single gas well, a part of a landfill, or a pipeline segment. In ideal conditions, these satellites discern even emissions amounting to about one hundred kilograms of methane per hour.

In the case of Las Dehesas, these satellite images are supplemented by flights of research aircraft equipped with instruments capable of mapping methane in detail of approximately one meter. Such maps literally show where gas is breaking through the surface cover of the landfill, where a filled layer of soil might be missing, or where gas has found a way along the edges of drainage and discharge structures. Together with field measurements at ground level, the entire data package turns invisible gas into a set of clearly recognizable, quantified sources.

Repairs at the landfill under satellite surveillance

One of the most important phases of the Madrid study took place between the spring and autumn of 2025. After the initial recording of the state, the landfill operator carried out a series of maintenance works: gas collection wells were serviced and upgraded, underground and above-ground pipes for transporting methane to energy facilities were checked and repaired if necessary, and methods of covering active and closed landfill surfaces were adjusted.

After these interventions, the same combination of measurement systems was used again during September and October 2025. Satellites recorded new scenes from orbit, aircraft flew over the landfill again, and teams on the ground recorded changes in gas concentrations near key points. The comparison of before and after, which scientists are currently analyzing in detail, should show how much specific interventions – for example, the remediation of a certain series of wells – truly reduced total emissions.

An important element of the entire process is also the speed of information exchange. The research team regularly provides the landfill operator with maps showing suspicious hotspots, and field staff can check the situation at those locations almost in real time. In many cases, scientists state, landfill employees were able to physically visit the problematic area in a short time, confirm the leak, and immediately plan or carry out remediation.

In this way, satellite and aerial measurements are transformed from abstract scientific data into a very concrete operational tool. For the city of Madrid, this means less uncontrolled methane in the atmosphere, but also a more precise insight into how much more effective the existing systems for collecting and utilizing landfill gas truly are after investments in maintenance. For scientists, it is an opportunity to calibrate gas release models and compare them with what satellites and instruments on the ground actually measure.

Who is behind the project: an example of cooperation between science, cities, and industry

The Las Dehesas project is not a classic academic study detached from everyday life. Landfill operators and the Madrid city administration have been involved from the beginning, openly sharing data on the operation of the facility – from the waste disposal schedule to the maintenance work calendar. Researchers attach satellite images, aerial measurements, and ground data to this information, creating a joint, transparent mosaic.

In addition to the University of Leicester and ESA, partners such as the company GHGSat, SRON from the Netherlands, the Technical University of Denmark, and the International Methane Emissions Observatory, which operates within the United Nations Environment Programme, are participating in the project. It is precisely IMEO and related initiatives that strive to consolidate data from various sources – national inventories, industry measurements, measurement campaigns, and satellite missions – so that decisions on emission reductions are based on the actual, verifiable state.

For landfill managers, such a project is an opportunity to compare different monitoring technologies, from classic networks of wells and probes to the latest space systems. For city authorities, it represents a tool with which they can show the public that they are actively managing emissions, and not just "proving compliance" with minimum legal standards. In a broader context, the study serves as a prototype for future links between satellite operators, scientific institutions, and local utility companies around the world.

Global network of satellites for methane: from Sentinel-5P to commercial constellations

The Madrid landfill is just one example in a much wider wave of projects relying on new satellite missions. In addition to the aforementioned Sentinel-5P, specialized missions have been launched into orbit in recent years with the main task of precisely detecting and quantifying methane emissions. Some of them are developed by public institutions in cooperation with NASA and other agencies, and others by private companies offering data to industry, governments, and international organizations.

By the end of 2025, the Canadian company GHGSat manages a constellation of sixteen satellites dedicated to precise monitoring of industrial emissions. Their instruments regularly fly over oil and gas fields, coal mines, steel mills, but also an increasing number of waste landfills worldwide. The data they collect serves both commercial clients, who want to identify methane losses as an economic opportunity, and public bodies, which monitor whether emission reductions have truly been achieved.

New publicly available missions that emphasize transparency are also coming into play. In August 2024, the Tanager-1 mission was launched as part of the Carbon Mapper coalition, which, using technology developed in NASA laboratories, strives to map large methane plumes from various sectors, including landfills, daily. A similar role was taken by the MethaneSat satellite, which was launched in early 2024 with the support of the Environmental Defense Fund organization and partners, and is designed to publicly publish data on the biggest polluters. Although the mission suffered a serious technical failure during 2025, early data sets are still used for analysis and the development of new monitoring approaches.

Data from different missions are increasingly being consolidated on open platforms. For example, the United Nations Environment Programme is developing systems like the Methane Alert and Response System (MARS) and the Eye on Methane portal, which integrate information from satellites, field campaigns, and industry reports. Such platforms allow detected methane leaks not to remain at the level of scientific work, but for information to be forwarded to competent authorities and operators to initiate concrete measures.

From orbit to policy: how satellite data change the rules of the game for landfills

Satellite measurements of methane were until recently primarily a source of data for scientific papers and global greenhouse gas inventories. However, as high spatial resolution and imaging frequency advance, it is becoming easier to link an individual gas plume to a specific facility or even a landfill cell. Thereby, satellites are also entering the domain of regulatory and judicial practice, where they can serve as additional evidence for initiating investigations or imposing fines.

In certain countries, discussions are already underway on how to accept satellite data as part of official monitoring systems for landfills and other facilities. Regulators recognize that satellites allow them a relatively cheap and independent insight into the state of hundreds of locations, without the need to send inspectors with measuring equipment to every landfill. At the same time, operators get the opportunity to proactively react to observed emissions and show that they take methane reduction obligations seriously.

It is especially important that satellite measurements do not remain isolated data islands. Projects like the Madrid one show how maximum value is achieved when they are combined with local knowledge of the facility, detailed field measurements, and clear remediation plans. Then satellite "pixels" stop being just a pretty map for presentations and become a tool that guides work crews on the ground daily.

What the results from Madrid mean for other landfills – and for cities like ours

Although Las Dehesas is a specific landfill with its own climatic, geological, and operational conditions, the methodology developed over Madrid can easily be transferred to other facilities. Many key components already exist: satellites tracking methane almost in real time, algorithms for plume detection, models of gas dispersion in the atmosphere, and standardized methods for estimating emissions at the landfill level.

For large cities in the European Union, including those in Croatia and the region, such projects offer a kind of "template" on how to combine the requirements of climate policy, waste legislation, and local emission management plans. A city that wants to reduce its carbon footprint can, for example, request that the landfill operator cooperate with research institutions and satellite operators, conduct a detailed measurement campaign, and based on the results create a plan for remediation interventions – from installing additional wells to better covering of surfaces and capturing gas for energy production.

It is important to emphasize that satellites are not a magic wand that can solve all problems with methane emissions from waste. They cannot replace well-designed gas collection systems, quality waste covering, modernization of landfills, and, finally, the processing and reduction of waste generation. But they can show where the biggest holes in the existing system exist and offer quantitative data on how much an intervention truly reduced emissions.

In the years to come, the combination of increasingly numerous satellites, sophisticated algorithms, and cooperation between cities, industry, and the scientific community will likely turn the story of the "invisible gas" into very concrete lists of locations, interventions, and emission reductions. The results of the Madrid study, whose scientific papers and detailed analyses are expected in early 2026, will serve as an important test of how far we can go in quantifying methane from landfills and directing measures to places where they will have the greatest effect.