And fortunately Chahine was proved right - NASA announced at the AGU Fall Meeting in San Francisco this week that it is making seven years of carbon dioxide data from AIRS available to the research community.
"We knew that AIRS would have the spectral resolution for measuring greenhouse gases," said Thomas Pagano, who is project manager for AIRS, "but we never expected the instrument to behave so well and be so stable."
The measurements have revealed that, contrary to common belief, carbon dioxide is not well-mixed in the mid-troposphere. "That means we need to improve the models" said Chahine, who compared the carbon dioxide's appearance to ink drops in water before they disperse. The information that AIRS can provide on the concentrations of carbon dioxide, carbon monoxide and methane in the atmosphere will help with this task.
The team found that when the jet stream is strong it can split the "lump" of carbon dioxide formed over North America into two; when the jet stream weakens, the two parts of the lump rejoin.
"AIRS is unique in that it provides global measurements of carbon dioxide levels daily and works in cloud," said Chahine, who reckons the gas is "unforgiving with respect to remote sensing". AIRS uses passive detection of infrared, taking 15,000 measurements a day at the level at which carbon dioxide is transported around the globe; it's the only instrument of its type that can "see through" cloud.
To do this, AIRS employs mathematical analysis. Clouds cause high frequency variations in temperature; the instrument separates these from the low frequency variations in temperature that it is trying to measure. Team member Eric Fetzer compared this to imaging a wall in a roomful of people by removing the quickly varying detail of human bodies from the smoothly varying wall. The only snag is the loss of some resolution - AIRS is a 13 km instrument but produces final data with a resolution of 50 km. "We can have our cake and eat it too," said Chahine.
The researchers say they are looking forward to feedback on their carbon dioxide data from the research community. All being well, AIRS will collect this data until 2017, when Aqua will run out of fuel. If AIRS does survive until then, it should overlap for four years with the Orbiting Carbon Observatory (OCO), which is due for a second attempt at launch in 2013 following its failure earlier this year. OCO had been scheduled to run three minutes ahead of Aqua, providing data that would have complemented AIRS by measuring carbon dioxide in the whole air column, rather than just in the middle atmosphere.
"We are keeping a warm spot for OCO in front of Aqua," said Chahine, who believes he has a technique up his sleeve for measuring carbon dioxide concentrations below 5 km with AIRS too. Data from OCO will provide a valuable means of cross-checking whether he is right.