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NASA / JPL-CALTECH
Building an image of CO2 is a complex undertaking that requires a lot of modeling
NASA has sent an instrument to the International Space Station (ISS) to help detect carbon dioxide on Earth.
OCO-3, as the observer calls it, was launched on a Falcon rocket from Florida in the early hours of Saturday.
The instrument is made from the remaining spare components after mounting a satellite, OCO-2, which was put into orbit to perform the same job in 2014.
The data from two missions should give scientists a more accurate idea of how CO2 is moving in the atmosphere.
One of the ways to achieve this lies in the different perspectives that OCO-2 and OCO-3 will get.
The first one flies over the world on what is called a sun-synchronous polar orbit, which causes it to see any place at the same time of day.
The latter, on the other hand, because it will fly aboard the station, will only see positions ranging up to 51 degrees North and South; and see them at different times of the day.
This is interesting because the ability of plants to absorb CO2 varies during the day. The OCO-3 dataset will have a lot to add to that of its predecessor.
"Getting these different information about the time of day since the orbit of the space station will be really valuable," BBC News, Nasa project scientist Annmarie Eldering, told BBC News.
"We have a lot of good arguments about daytime variability: the performance of plants at different times of the day, what could we possibly learn, so I think it's going to be exciting from a scientific point of view."
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NASA / JPL-CALTECH
OCO-3 uses spare parts from the construction of OCO-2
The missions of the Orbital Carbon Observatory (OCO) attempt to dispel the uncertainties related to the CO2 cycle: how and where greenhouse gases are emitted (sources), and how and where they are absorbed (wells) .
Humans cause an imbalance in this cycle, increasing the concentration of gas in the air.
At present, anthropogenic activities release almost 40 billion tonnes of CO2 per year, mainly from burning fossil fuels.
About half of this amount stays in the atmosphere, which contributes to warming.
About half of the other half is absorbed by the ocean, the rest being dumped into earthen wells. But these "budgets" are imperfectly characterized. Some important sources and sinks, both human and natural, require a more complete description.
OCO instruments incorporate spectrometers that break down the color of the sun reflected off the Earth's surface, and then analyze the spectrum to determine the amount of carbon dioxide present.
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NASA
The ISS also flies north as London, UK, and south as far as Patagonia, Argentina
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NASA
The OCO-3 instrument will look at the Earth from the Japanese Kibo laboratory
The interpretation of the data is complex because it requires the use of models to explain how the gas is mixed in the atmosphere.
The space station's instrument brings a new tip to the OCO's observations: a system of pivoting mirrors that allows the spectrometer to scan a much wider area of the Earth's surface than would normally be the case.
This "instant" mode means that CO2 maps can be constructed in a single pass on a target of particular interest, such as a megacity – a task that will take OCO-2 for several days.
"Snapshot mode allows us to capture snippets of data over an area of about 80 km by 80 km in two minutes, and at the present time we expect to spend about a quarter of our time creating of those mini-cards, up to 100 per day, "said Dr. Eldering. I said.
OCO-3 will be positioned on the Japanese segment of the space station. Its lifetime on mission is therefore rather fixed at three years. Indeed, the position he takes on the observation platform is already reserved for a future instrument.
Carbon monitoring, however, will see many more satellite systems launched in the coming years.
Europe is considering a constellation of observers in its Sentinel series that will map CO2 over a much larger area than the OCO, but with the same precision.
This in-orbit network would even control the commitments made by each country to reduce carbon emissions under international agreements such as the 2015 Paris Climate Agreement.
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