GPS radio occupations coming of age: Spacecraft launches add two new instruments for climate monitoring

Global Positioning System (GPS) radio occultations are active limb soundings that measure the time delay of a GPS signal propagating through the atmosphere. This time delay can be related to vertical profiles of atmospheric refractivity from which highly accurate profiles of geopotential height, temperature, pressure, and specific humidity are derived. With their global coverage, self-calibrating nature, penetration through clouds, and high vertical resolution, atmospheric radio occultations are coming of age and hold great promise for weather prediction and climate monitoring.