Physics-Based GNSS-R Revolutionizes Independent Global Soil Moisture Retrieval from Space

For decades, global soil moisture monitoring from space has depended on external reference products for calibration, limiting transparency, transferability, and consistency. GNSS-R, a promising technology, also largely relied on these external datasets. This practice, while stabilizing initial retrievals, created a fundamental bottleneck for truly independent and robust global soil moisture data, complicating long-term consistency as reference products evolve.

A new physics-based framework, PHYsics-based Soil rEflectivity Retrieval (PHYSER), is now changing this paradigm. Published in the Journal of Remote Sensing by researchers from the Chinese Academy of Sciences, Peking University, and the China Meteorological Administration, PHYSER enables independent spaceborne GNSS-R soil moisture retrieval, free from external reference products. It achieves this by accurately reconstructing soil surface reflectivity through comprehensive physical corrections for system biases and land surface effects.

Validated using a year of data from China's BuFeng-1 A/B satellites, PHYSER-based retrievals showed strong consistency with independent SMAP products, ERA5-Land, and in situ measurements. This breakthrough offers robust, scalable soil moisture data without statistical imitation, providing transparent and transferable results vital for future Earth observation, climate modeling, and agricultural decision-making.