Overview and outlook of GNSS remote sensing technology and applications

Abstract

The Global Navigation Satellite Systems (GNSSs), including the United States Global Positioning System (GPS), Russian GLONASS, the European Union's Galileo, and China's BeiDou, provide L-band microwave signals with high temporal resolution. These systemshave extended the applications of the GNSS from positioning/navigation to remote sensing. Since the 1990s, the versatile refracted GNSS signals have been successfully demonstrated to sound the ionosphere and troposphere. In the pasttwo decades, reflected signals, which involve making measurements of the reflections from the Earth, have shown theircapacity for earth observations over wateror land. On the basis of such background, GNSS remote sensing, as a hybrid of GNSS and remote sensing, has been developed over the years. The concepts of GNSS remote sensing can be summarized into two categories: GNSS refractometryand GNSS reflectometry (GNSS-R). The applications of GNSS remote sensing involves atmospheric water vapor, seismo-ionospheric disturbances, oceans, lands, hydrology, and the cryosphere. To further promote the applications of the GNSS remote sensing technology in atmospheric, seismic, and water cycle studies, this review systematically introduces the international and domestic forefront of GNSS remote sensing technology and its applications, with a focus on GNSS/meteorology, GNSS ionospheric seismology, GNSS radio occultation, ocean observations, land applications, cryosphere applications,and missions of GNSS-R. We also discuss and provide an overview of the bottlenecks related to the further development of each branch of GNSS remote sensing. The next generations of GNSS systems, especially GPS III and BeiDou II, are expected to show improved performance and offer excellentcapabilities to users around the globe. This study can provide references for the future development of GNSS remote sensing technologiesand otherrelated subjects.