ESA CCI SM v9: advancements in global satellite soil moisture records

Soil moisture plays a pivotal role in the Earth system, exerting a profound impact on a wide range of environmental and climatic processes. Consequently, accurate monitoring of soil moisture is essential for climate research, environmental management, and the development of adaptation strategies under changing climate conditions. For these purposes, datasets developed within the ESA CCI Soil Moisture (SM) project provide homogenized long-term records of surface soil moisture. The newest suite of products, ESA CCI SM v9.2, consists of daily, global soil moisture estimates derived from a large set of historic and operational microwave sensors. Its data spans a period of over 45 years, produced both from passive and active observation systems. To address advancing user requirements, a set of science products complements the original SM Climate Data Records: A) gap-free surface soil moisture, filling data gaps due to missing satellite overpasses by means of a statistical method, B) satellite-only sensor harmonization, providing a record independent of land surface model data. In addition, v9 introduces three novel datasets: C) estimates of root-zone soil moisture, necessary to assess processes beyond the soil surface layer, D) increased spatial resolution of 0.1°, enabling research on mesoscale land-atmosphere interactions and E) soil freeze/thaw state, an important parameter for the interpretation and flagging of soil moisture retrievals.