Satellites can track CO2, methane in metros like Mumbai and Delhi: IIT Bombay researchers

Mumbai, Oct 17 (PTI) Researchers at Indian Institute of Technology Bombay (IIT Bombay) have found that remote sensing data can be used to reliably measure the levels of carbon dioxide and methane in metro cities like Mumbai and Delhi.

As India lacks an extensive network of ground stations to measure greenhouse gases (GHGs), IIT Bombay researchers Prof Manoranjan Sahu and Adarsh Alagade turned to satellite data.

Using satellite derived measurements, they noticed that greenhouse gas (GHG) levels in Delhi and Mumbai are on the rise and show seasonal and spatial variations.

Further, the researchers also developed city-specific statistical models to forecast the level of GHGs.

They demonstrated that remote sensing data can be used to reliably measure the levels of carbon dioxide and methane in metro cities.

"By identifying trends and hotspots, satellite-based monitoring gives policymakers evidence to target the worst sources - for instance, prioritising landfill gas capture, traffic management in high-emission corridors, or industrial emissions enforcement - and to evaluate the real-world impact of policies over time," explained Prof Sahu regarding the benefit of using satellite-derived data.

The researchers used data from NASA's Orbiting Carbon Observatory-2 (OCO-2), which traces carbon dioxide, and the European Space Agency's Sentinel-5P, which tracks methane.

As these satellites did not provide direct emission numbers, the researchers relied on specialised algorithms to extract the necessary values from the raw data.

To ensure reliability, the IIT researchers validated their satellite readings against the Total Carbon Column Observing Network (TCCON), a network of ground level measuring stations, spread globally, offering highly accurate measurements of CO and CH.

Using satellite-derived measurements the researchers observed methane and CO concentrations over the last few years.

This data also alerted the researchers to the emergence of methane hotspots, which were typically around regions with wastewater, landfills or higher industrial activities.

The identification of such hotspots and the risks posed by waste management and rapid urban growth demonstrate how satellite data can play a major role in informing targeted policy interventions. CO concentrations were also observed to be rising over the years.

The researchers used the satellite-derived data to fine-tune and adapt SARIMA (Seasonal Autoregressive Integrated Moving Average), which is often used for forecasting future values based on past data, for both Delhi and Mumbai.

However, there are limits to using satellites, Prof Sahu cautioned.

"Satellites are powerful but not perfect. Clouds, dust and city smog can hide or distort measurements. Satellites give snapshots rather than continuous local records. All of these factors need careful handling before satellites are used for regulation," he pointed out.

He said satellites and ground stations together can reconcile top-down observation with bottom-up measurements, improving the credibility of emission estimates and climate policy.

Moving ahead, new tools such as machine learning can potentially enhance the scope of predictions and estimates, said Prof Sahu.

"Machine learning (ML) is a powerful tool and will play a big role, but the best future systems mix machine learning with physics-based models, improved satellite sensors, and ground data," he added. PTI SM BNM