HydroGNSS from below

The HydroGNSS mission consists of two identical microsatellites orbiting Earth on opposite sides of the planet, 180 degrees apart, to provide maximum global coverage.

Each HydroGNSS satellite carries a Delay Doppler Mapping Receiver that listens to GPS and Galileo satellite signals. It receives the direct signals through a top-facing (zenith) antenna, and the reflected signals – bounced off Earth’s surface – through a bottom-facing (nadir) antenna. By comparing these two, the satellites can create Delay Doppler Maps to study hydrological variables like soil moisture and inundation.