This cannot always be done by scientific studies and laboratory experiments alone, but often requires dedicated measurements using aircraft or towers as a proxy for the satellite.
In partnership with universities, science institutes and other space agencies, these campaigns are carried out all over the world, from the icy reaches of the Arctic and Antarctica to tropical rainforests.
As part of these large international efforts, scientists venture out to some of the most inhospitable places on the planet to take measurements from aircraft, from towers, from ships and down on the ground.