Flooded forest, Czech Republic

ESA’s SMOS satellite is not only proving its worth by mapping soil moisture and ocean salinity, this multifaceted satellite has now shown that it can ‘see’ through vegetation to monitor wetlands for a better understanding of Earth’s carbon cycle.

It is widely appreciated that wetlands are important resources of freshwater and are rich in biodiversity.

However, it is less well known that wetlands also emit large quantities of methane – in fact, they contribute more methane to the atmosphere than any other natural source. Wetlands can also be both sources and sinks of carbon.

Although there is less methane in the atmosphere than carbon dioxide, methane is a much more powerful greenhouse gas. It is estimated that atmospheric methane was responsible for about 20% of the rise in global temperatures last century.

Methane emissions are mostly a result of human activity, but wetlands are thought to be responsible for about 20–40% of global emissions.

SMOS measurements

The waterlogged wetland soil is a prime habitat for anaerobic microbes. It is the anaerobic decomposition of organic matter covered by water that produces large quantities of methane.

ESA’s SMOS water mission carries a novel microwave sensor to capture images of ‘brightness temperature’ to derive information on soil moisture and ocean salinity. This information is improving our understanding of water cycle.

However, SMOS is showing itself to be a very versatile tool and extending its usefulness to other areas of Earth science.  

Surpassing expectations, SMOS is also being used to monitor thin Arctic sea ice, map freezing soil, determine wind speeds under hurricanes and monitor ocean eddies. Extending the value of SMOS even further, studies have shown that monitoring wetlands could be added to the mission’s repertoire.

Because SMOS measures emitted radiation at a rather long wavelength of 21 cm, vegetation and the atmosphere have little affect on the observations. This means it is possible to look at how wetlands change over time.

Such information is extremely valuable for our understanding of the role that wetlands play in the carbon cycle and how they contribute to atmospheric methane.

Inundation from multiple satellites

Moreover, it has recently been demonstrated that observations from SMOS can reproduce features seen in complex datasets that include observations from many satellites such as that shown in the image on the left.

Catherine Prigent from the Paris Observatory explains, “SMOS offers the opportunity to implement fast and easy single satellite algorithms for monitoring wetland areas.

“This complements current methods of analysis that require a lot of work to blend the different products.”

A future SMOS product could be interesting for the GlobWetland II project. This programme, which is funded through ESA’s Earth Observation Data User Element, is helping to establish the Global Wetlands Observing System.

Here, high-resolution optical data such as that from the Sentinel-2 mission, could be combined with the coarse-resolution SMOS observations to make optimal use of available remotely-sensed information.

SMOS in orbit

By mapping wetlands and soil moisture, SMOS can also lead to a better understanding of the exchange processes between Earth’s surface and the atmosphere, including carbon fluxes.

Integrating SMOS observations into global carbon models is another novel application that was presented during the SMOS land application workshop held in February in Italy.