MethaneSAT – building accurate models

Methane emissions come from many sources – transport, waterlogged soils, ruminant animals, landfills and more. Atmospheric models help to ‘untangle’ where the emissions come from.

Dr Sara Mikaloff-Fletcher and Dr Beata Bukosa (NIWA) and Professor David Noone (University of Auckland) explain how atmospheric and ground-based measurements ensure these models are accurate.

Jargon alert:

• Air column: a vertical column of air from the top of the atmosphere down to ground level. The atmosphere is dynamic, which means the wind blows gases around. Gases and other substances in the air column can come from different locations.

• Atmospheric transport model: a computer simulation of greenhouse gases, air pollutants, water vapour and other particles moved by the wind and swirling air currents.

• Ground-truthing: the process of gathering data to test the accuracy of a scientific model.

Questions for discussion:

• How is playing computer games like The Sims or Minecraft similar to building scientific models?

• What do you think Beata means when she says that, in their models, they build the atmosphere?

• What would you include if you were building the atmosphere?

• Why is it important to know where the methane emissions are coming from?

• What does Sara mean when she says having two approaches give the same answer builds confidence in their measurements?

Transcript

Dr Sara Mikaloff-Fletcher

Principal Scientist (Carbon, Chemistry and Climate), NIWA Science Leader, MethaneSAT

Our role in the MethaneSAT mission is to develop the ability to use those satellite measurements to detect agricultural emissions from both animals and also rice paddies by developing the modelling tools to be able to infer the emissions from what the satellite actually sees. So what the satellite measures is the methane concentration in the air column. Methane emissions are the amount of methane that’s being put into the atmosphere from different emission processes – whether it’s fossil fuels, agriculture or anything else.

Dr Beata Bukosa

Atmospheric Modeller, NIWA

There are lots of models involved in this project. So the first thing that we need to do is make sure that all of those models are set up and working the way we are expecting them to work. Broadly speaking, a model is anything that can mathematically or literally describe some real-life process.

For example, as a kid, I really liked to play The Sims. It is a game where you build different things. You build a house, you build the walls, you add windows, you add people in it.

And this is really similar to the models we’d use, but we don’t build houses, we build the atmosphere. And then we don’t put windows, we put clouds in it and different gases like greenhouse gases that we have. And basically, what we’re trying to do is mathematically replicate what we see in the atmosphere in a model.

There are different things that can inform models. In the models that we are going to use as part of the MethaneSAT project, this will include the actual measurement that the satellite is going to collect and also the ground-based measurements that we’re going to collect as part of the project.

You also need information about the winds and other meteorological fields. One of the big challenges is the atmospheric transport model that we are using. You need really good information about the motion of air – where the air comes from and how it moves around. And for this, we have a number of different models to use.

So the best way to make sure that models are accurate is to compare it to something that we know very well, which are the measurements – which means we’re going to compare the two values from the ground and from the space.

Professor David Noone

Buckley-Glavish Professor of Climate Physics, Department of Physics, University of Auckland

So while we’re doing ground-truthing of the primary measurement itself – the amount of methane – what we’re really doing is doing the measurements necessary to do that backtracking problem to deliver methane sources – amount of methane that’s put into the atmosphere. So when we think about ground-truthing, we really mean this integrated approach to going through from ‘Where is the methane emitted?’, ‘How is it transported through the atmosphere?’, then ultimately, ‘Where does it end up?’

We have a hierarchy approach to making measurements. One is using aircraft to have high-precision instrumentation to measure the amount of methane up and down in the atmosphere. Another approach is these ground-based instruments that are very similar to the instruments on board MethaneSAT and other satellites.

Dr Sara Mikaloff-Fletcher

The gold standard for that testing is what’s called the Total Carbon Column Observing Network – TCCON. We’re very lucky here in Aotearoa New Zealand to have one of the two founding TCCON stations. And we’ve started using those surface observations to backtrack and estimate our methane emissions from atmospheric data. And so far, that work has been really successful. When you have two totally interdependent approaches that are giving you the same answer, that’s an answer you can have a lot of confidence in.

Acknowledgements Dr Sara Mikaloff-Fletcher, NIWA Professor David Noone, University of Auckland Dr Beata Bukosa, NIWA Satellite view of New Zealand and Australia on Earth, antartis, 123RF Ltd SIMS gaming, ‘The Sims House’, Sims Magic, CC BY 3.0 Animation of MethaneSAT satellite above Earth, and small aircraft collecting data (in USA), scientists in van, Permian Basin methane mapping project with Scientific Aviation and the University of Wyoming, all courtesy of MethaneSAT and the Environmental Defense Fund (EDF) Satellite image of New Zealand, NASA, CC BY 2.0 Wind model, laser beams in night sky and Lauder Atmospheric Research Station, NIWA