Atmospheric and Ocean Sensing with GNSS

The 1980s and 1990s saw the Global Positioning System (GPS) transform space geodesy from an elite national enterprise to one open to the individual researcher. By adapting the tools from that endeavor we are learning to probe the atmosphere and the ocean surface in novel ways, including ground-based sensing of atmospheric moisture; space-based profiling of atmospheric refractivity by active limb sounding; and global ocean altimetry with reflected signals. Ground-based GPS moisture sensing is already being tested for weather prediction. Limb sounding is less mature but offers a variety of attractions, including high accuracy, stability, and resolution; all-weather operation, and low cost. GPS “reflectometry” is least advanced but shows promise for a number of niche applications.