From Ground to Space: Building Reliable Measurements of Greenhouse Gases
At the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), many efforts are made to contribute to high-quality satellite and in-situ measurements of greenhouse gases and other compounds that play a role in our climate and air quality. This ranges from involvement in mission preparations to data-processing and validation campaigns in order to acquire the most accurate information possible.
BIRA-IASB scientist Mahesh Kumar Sha gave an interview on Traceable Measurements for Greenhouse Gas Monitoring at the BIPM’s (Bureau International des Poids et Mesures) Scientific Conference during the 150th Anniversary of the Metre Convention.
How We Measure Greenhouse Gases from Space
How can scientists measure greenhouse gases accurately across the entire planet — from the air we breathe at Earth’s surface to altitudes hundreds of kilometres above us? And how can data collected by different instruments, under different conditions, be made reliable and comparable over time?
These questions were at the heart of a conversation between the Bureau International des Poids et Mesures (BIPM) and Mahesh Kumar Sha during the BIPM Scientific Conference held to mark the 150th anniversary of the Metre Convention. In a short video interview, Mahesh explains how space-based and ground-based observations work together to provide a trustworthy picture of our changing atmosphere.
From satellites to the ground
Satellites play a crucial role in monitoring greenhouse gases because they provide near-global coverage on a daily basis. By measuring sunlight reflected from the Earth’s surface and radiation scattered within the atmosphere, satellite instruments can retrieve total and/or partial column concentrations of gases such as carbon dioxide and methane over vast areas.
However, as Mahesh explains, these measurements are typically made from a distance of around 800 km, which introduces significant challenges. Factors such as surface reflectivity (albedo), aerosols, humidity and the way light is scattered in the atmosphere all affect the signal received by the satellite. Unlike a camera on Earth, satellites cannot adjust their settings in real time, so scientists must correct for these effects after the measurements are taken.
Mahesh says:
These uncertainties mean we need reliable reference measurements. That’s where ground-based observations come into play.
Building confidence through reference networks
Ground-based measurements allow scientists to observe greenhouse gases directly in the air at specific locations (in situ measurements) or to measure the total and/or partial amount of gas in a vertical column from the surface to the top of the atmosphere (remote sensing measurements). The Integrated Carbon Column Observation System (ICOS) is one such in-situ network contributing to the measurement of greenhouse gas in Europe. Established networks such as the Total Carbon Column Observing Network (TCCON), the COllaborative Carbon Column Observing Network (COCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC) provide high-quality remotely sensed reference data that are essential for validating and calibrating satellite observations.
Mahesh and his colleagues are also working to complement these traditional networks with portable, lower-cost instruments based on Fourier Transform Spectrometry. These instruments have proven to be very reliable and are able to provide measurements of comparable quality as the established networks. By characterising and deploying these instruments at different sites, the team aims to fill gaps in the global observing system, particularly in regions that are currently under-sampled and are critical for the understanding of the carbon cycle and reducing the uncertainties.
Towards better emission estimates
Combining satellite data with a dense and well-characterised ground-based network allows scientists to identify biases, reduce uncertainties and better determine the true state of the atmosphere. This, in turn, leads to more accurate estimates of greenhouse-gas emissions at global and regional scales.
These efforts directly support emerging international initiatives such as the WMO Global Greenhouse Gas Watch (G3W), which aims to provide high-resolution emission estimates — on the order of 100 km by 100 km — using advanced inverse modelling techniques.
Mahesh explains:
In the end, what we want is to identify emissions at their source. By strengthening the measurement infrastructure from the ground to space, we can provide the confidence users need to rely on these data for climate science and policy.
The interview highlights how metrology, atmospheric science and international collaboration come together to underpin one of the most important measurement challenges of our time.
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