GNSS Reflectometry for Soil Moisture Retrieval: Methods and Approaches - A Review

Soil moisture, an essential component of the hydrological studies, plays a pivotal role in agricultural irrigation, weather systems, and global water cycle dynamics. Conventional methods of assessing soil moisture, such as in situ measurements, face limitations in coverage, scalability, and their ability to contribute to disaster prevention and insights into the water cycle. Microwave remote sensing satellites offer advantages like sensitivity, cloud penetration, and independence from solar energy but fall short in providing high temporal resolution. New advancements in Global Navigation Satellite Systems (GNSS) have expanded their utility beyond positioning and navigation with the introduction of GNSS Reflectometry (GNSS-R), a technique for estimating soil moisture. This system can function as an altimeter or scatterometer, estimating land or ocean surface characteristics like height, roughness, and dielectric properties. One can estimate geophysical parameters such as snow depth, sea ice, winds, water level, vegetation, and soil moisture using a variety of techniques. The paper describes retrieval strategies that focus on the benefits and drawbacks of both remote sensing and in situ measurement techniques. It focuses on the underlying concepts of GNSS technology, describing how it detects reflected signals on the surface of the earth to estimate soil moisture. It emphasizes GNSS-R benefits of GNSS-R, including low cost, global coverage, all-weather capability, and high spatial and temporal resolutions. In this paper, the noteworthy advancements in GNSS-R soil moisture monitoring are highlighted and investigates how GNSS-R may provide insightful information about soil moisture dynamics. By using cutting-edge remote sensing techniques, it supports a range of applications and tackles environmental challenges.