Land Remote Sensing Applications Using Spaceborne GNSS Reflectometry: A Comprehensive Overview

The refracted, reflected, and scattered signals from global navigation satellite systems (GNSSs) have been successfully used for remote sensing (RS) of the Earth's surface and atmosphere, demonstrating their potential for sensing the atmosphere, oceans, land surface and cryosphere. As an emerging RS technology, spaceborne GNSS reflectometry (GNSS-R) has been widely used in the field of land RS, with unique advantages such as high spatial and temporal resolution, low observation cost, wide coverage, and all-weather operation. In recent years, the successful launch of several spaceborne GNSS-R satellites has opened new opportunities in this field. The aim of this article is to provide a comprehensive overview of the breakthrough applications of spaceborne GNSS-R technology in the key areas of soil moisture, soil salinity, vegetation monitoring, soil freezing and thawing, flood detection, inland water bodies, wetland dynamics, forest fire disturbances, and land topography measurements, as well as possible future research directions. In addition, this article also emphasizes the contribution and role of China's recently launched Tianmu-1 constellation (as of 5 January 2024, 23 satellites have been in stable operation in orbit) in the development of spaceborne GNSS-R technology and explores the future development direction and prospects of this technology. By comprehensively analyzing the latest progress and innovative achievements of relevant research, the significant impact of this technology on land RS applications in environmental monitoring, resource management, and disaster warning has been highlighted. Through a comprehensive summary of these fields, the enormous potential of spaceborne GNSS-R technology in promoting sustainable development and ecological protection has been revealed.