Spaceborne GNSS Radio Occultation Instrumentation for Operational Applications

Radio occultation (RO) instruments using GNSS signals are specialised spaceborne receivers designed to provide highly accurate measurements from which one can derive vertical profiles of the temperature, pressure and humidity in the atmosphere, as well as profiles of electron content in the ionosphere. A family of operational RO instruments is being developed for a number of European space projects since 1996. The basic functions of the instrument include: reception of signals that have crossed the atmosphere at varying altitudes by means of two antenna arrays; acquisition of such signals, also during the rise (ascending) RO events, when a signal first appears after crossing dense tropospheric layers causing large dynamics in amplitude and phase; robust signal tracking to provide precise amplitude and phase measurements; on-board processing to support RO event predictions, also to aid the tracking. We summarise the main requirements and illustrate the main technical features adopted. The expected performance is also presented.