GNSS radio occultation

GNSS radio occultation uses a receiver on a low-Earth-orbit platform to track GNSS signals as they set or rise behind the atmospheric limb. Refraction along the limb path changes signal delay and bending angle; retrieval processing converts those measurements into refractivity and then into atmospheric temperature, humidity, pressure, and related profile products.^[1][2]

This method is direct atmospheric and ionospheric sounding. It also supports space-weather profiling because the same occultation geometry can retrieve ionospheric electron density and total electron content products.^[1][3]

GNSS radio occultation is distinct from GNSS reflectometry. Radio occultation uses direct signals refracted through the limb for vertical atmospheric and ionospheric profiles. GNSS reflectometry uses reflected navigation signals from the surface to retrieve ocean wind, soil moisture, sea-ice, or roughness properties.