Aquarius Satellite Sensor (00:00:37)[24-Feb-10] One thing to note about the Aquarius satellite is that it's what we call a "passive" satellite. Even though it takes a lot of work to get up there and a lot of people are working to put it up there, what it's doing is actually recording the wavelengths that the earth is radiating. So some satellites are "active": so they are sending a signal down through the atmosphere to earth's surface and then they are recording that signal that comes back. But when we're trying to measure the sea surface salinity, the Aquarius satellite will be recording the microwaves that the earth is sending back out to the atmosphere and space. Credit: Susan Lozier.