A watershed boundary is a line you can't see from the ground. From orbit, it starts to show. We use three satellites, each reading the terrain a different way.

Lidar, for the shape

A laser sweep that strips the trees and returns bare earth. Ridges and channels pop out of the noise, and the divide — where rain chooses left or right — draws itself.

Radar, for the water

Surface-water extent, day and night, through clouds. It shows us where the river actually is, not where the old map said it was.

Gravity, for the aquifer

A pair of satellites that weigh groundwater from its tiny tug on orbit. It's how we see the basin below, refilling or draining, month to month.

Three instruments, one watershed. The map is the sum.