In the early 1990s, Katzberg and co

In the early 1990s, Katzberg and colleagues at NASA were asked to evaluate a U.S. Navy satellite for a civilian application in global ocean altimetry. The U.S. Navy was beginning to use GPS in their satellites and the team became intrigued with the question of whether the GPS signals could reflect off the surface of the ocean.

"Normally GPS signals go to a receiver in your car or cell phones, but some of it reflects off surfaces," Katzberg told National Geographic. "It's an incidental thing that turns out to be pretty practical, especially because GPS now illuminates pretty much the entire Earth