People may be able to see a Nasa research plane as it flies low over the South Island today collecting air samples as part of an international mission.
The flying laboratory will take off from American Samoa and land in Christchurch, after passing over Niwa's atmospheric research station just north of Alexandra.
Niwa principal scientist for atmosphere and climate Olaf Morgenstern said the plane would be noisy and flying low.
"Having this data set available, over these very large ocean basins, is quite valuable indeed.
"People have of course flown planes before but often these data sets are much smaller, so you go for a flight or two and you measure in a limited region, and this plane is measuring all the way from Alaska to New Zealand to South America to Greenland.
Mr Morgenstern said such data was expensive to collect.