EXPLAINED | Can Satellites Tell Mumbai Which Landfills to Fix First?

A satellite passed over Mumbai on April 3, 2026, and picked up two trails of methane from the Kanjur landfill. Carbon Mapper, the organisation that analysed the image, estimated that the two trails together pointed to a release of about 3,300 kilograms of methane an hour at the time. The same satellite had detected methane coming from two locations within the landfill on an earlier pass, in February 2025.

On November 7, Reuters reported a problem that helps make sense of those images. At Seymen, a landfill outside Istanbul, operators capture gas and use it to make electricity. A team at the University of California, Los Angeles, found that methane was still escaping in large amounts, based on repeated satellite readings. The report came two days before the opening of COP31, the UN climate conference in Antalya, Türkiye. Mumbai already has images of its own leaks. The question is what the city can do with them.

Why does a landfill make methane?

Bacteria break down food scraps and other organic material buried under layers of rubbish. Once the oxygen runs low, some of those microbes produce methane. A pile of yesterday’s waste can keep making gas long after the truck has left.

Methane traps heat in the atmosphere. A landfill can collect some of the gas by drawing it through wells and pipes. The collected gas can be burned off or used as fuel. Gas can still escape from areas where waste is uncovered or where the collection system is damaged or incomplete.

How can a satellite see a gas we can’t?

The Tanager-1 satellite measures light reflected from the ground. Methane absorbs certain wavelengths, leaving a signature in that light. Scientists look for the signature across the image. When it extends downwind, it can reveal a plume, a trail of gas drifting away from its source. Researchers can use the plume and wind information to estimate how fast the gas was escaping.

The picture can narrow a search from an entire waste site to a part of it. Someone still has to visit the site to check whether the gas is coming through uncovered waste, a damaged pipe or another route.

What exactly did the Mumbai passes find?

Carbon Mapper reported methane at seven waste sites on February 9, 2025, and six on April 3, 2026. Some appeared on both passes. Count each site once and the total is nine across the Mumbai region.

The April estimate of 3,300 kilograms an hour at Kanjur combines the two nearby plumes because the team could not reliably separate their rates. It describes a release when the satellite passed. Two readings more than a year apart show that emissions were detectable on both dates. Establishing an annual total or a trend would take more observations.

Why does Istanbul matter for Mumbai?

Seymen shows why installing pipes and reporting how much electricity they help generate only tells part of the story. Gas can reach the power plant and escape from the same landfill. The Turkish environment ministry told Reuters that intermittent satellite observations could not establish the site’s annual emissions. The operator said a particularly high reading came while part of the landfill was uncovered for work on the gas-collection pipes.

That explanation gives engineers something to check. Match the date and location of a plume to the site’s maintenance log. Look for another plume once the work is finished. Compare the overhead picture with measurements taken on site. That is how an image can lead to a repair and then help check whether it worked.

Could the images explain the smell around Kanjur?

Methane itself has no smell. Landfill gas can contain compounds that do, including hydrogen sulphide. A methane image cannot establish what residents smelled, what reached their homes or what concentrations they were exposed to. Those questions require measurements at ground level and information about where the wind was blowing.

In an October 22 order, the Bombay High Court recorded a Maharashtra Pollution Control Board notice requiring continuous air monitoring at the Kanjur processing plant for methane and several other gases, including hydrogen sulphide. On November 3, the court appointed three advocates to help it identify effective measures over the recurring odour complaints. The satellite and the court proceedings are asking questions that meet on the ground. Where is the gas getting out, and what is reaching the neighbourhood?

Which site should Mumbai fix first?

Kanjur is a defensible place to start inspecting. The satellite found emissions there on both passes, and there is already a regulatory record to check against. A reliable ranking across the region would need more repeat passes and ground measurements, and operators would need to show what they repaired and whether emissions fell afterwards.

There is also a job upstream. India’s solid-waste rules, in force since April 1, 2026, require waste to be separated into four streams at source, including wet waste. Keeping food scraps separate makes it possible to send them for composting or controlled treatment before they reach a dump. At Kanjur, the near-term test is whether inspectors can match a plume to a source, fix it and show that the release has fallen.