GNSS radio occultation technique for near-Earth space environment detection

Since the GPS/MET mission, Global Navigation Satellite System (GNSS) based radio occultation (RO) technique has been a powerful technique to detect the near Earth's space environment. Up to date, there has been more than 20 launched low Earth orbit satellites equipped with GPS RO receiver, with COSMIC was the first constellation dedicated for RO. These RO data are widely used in numerical weather prediction, climate and global change, and space weather monitoring and ionospheric research. With the success of COSMIC, the corresponding partners are moving forward with a follow-on RO mission, named COSMIC-2, which will ultimately place 12 satellites in orbit with two launches approximately in 2016 and 2019, respectively. Each COSMIC-2 satellite will carry an advanced GNSS RO receiver that will track both GPS and GLONASS signals, with capability for eventually tracking other GNSS signals from such as the Chinese BeiDou and European Galileo system, as well as two secondary space weather payloads to enhance space weather monitoring. COSMIC-2 will provide 4 similar to 6 times the number of atmospheric and ionospheric observations that were tracked with COSMIC. In this article we will focus on COSMIC/COSMIC-2, discuss the history of RO and some key technique issue, and review some scientific achievements. In addition, we will look into the future of RO technique including technique improvement and multiple RO missions of opportunity.