**3. Conclusions and Final Remarks**

NASA's CYGNSS 8 microsatellite-constellation is the first-ever operational GNSS-R mission, revolutionizing several scientific fields within our community, and attracting new members from different communities such as microwave radiometry and SAR. The number of GNSS-R scientific publications within our community continues to increase significantly thanks to the open-access CYGNSS products available at the PODAAC. This was a nice start, but the CYGNSS Science Team is a dynamic community always looking to improve products and apply them to new scientific applications. In this scenario, around 50% of the Science Team members are now involved with applications over land surfaces, including SMC, AGB, and water surface. The key enabling events were improving calibration procedures, product spatial resolution (e.g., reducing date integration to 0.5 s from 1 s), geolocation, metadata quality, and a more agile web for downlinking data.

The recent mission extension by NASA will enable the continuation of investigations by the CYGNSS Science Team. We will continue to contribute to the wider remote sensing community with our new and novel results, with the objective of advancing our understanding of key dynamic processes over the Earth's surface. With this article, we welcome new members to participate in the CYGNSS mission.

**Author Contributions:** Conceptualization, C.R. and H.C.-L.; methodology, C.R. and H.C.-L.; writing original draft preparation, C.R., H.C.-L., R.A., A.B., J.A.C., M.M. and A.W.; writing—review and editing, C.R., H.C.-L., R.A., A.B., J.A.C., M.M. and A.W.; visualization, C.R. and H.C.-L.; supervision, C.R. and H.C.-L.; project administration, C.R.; funding acquisition, C.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported in part by the NASA Science Mission Directorate contract NNL13AQ00C with the University of Michigan.

#### **Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **Abbreviations**

Acronyms

Above Ground Biomass (AGB) Advanced Land Observing Satellite-2 (ALOS-2) Advanced Microwave Scanning Radiometer (AMSR-2) Advanced SCATterometer (ASCAT) Artificial Neural Network (ANN) Bistatic Radar Cross Section (BRCS) Climate Data Record (CDR) Contiguous United States (CONUS) Cyclone Global Navigation Satellite System (CYGNSS) Delay Doppler Map (DDM) Delay Doppler Mapping Instrument (DDMI) Digital Elevation Model (DEM) Disaster Monitoring System-1 (DMC-1) Earth Observation (EO) Earth System Science Pathfinder (ESSP) End-to-End Simulator (E2ES) European Centre for Medium-Range Weather Forecasts (ECMWF) European Space Agency (ESA) Flight Model (FM) Food and Agriculture Organization (FAO) Fully Developed Seas (FDS) Physical Oceanography Distributed Active Archive Center (PODAAC) Geophysical Model Function (GMF) Global Forecast System (GFS) Global Navigation Satellite Systems (GNSS) Global Positioning System (GPS) Institute of Space Sciences (ICE) Institute of Space Studies of Catalonia (IEEC) Intermediate Frequency (IF) International Soil Moisture Network (ISMN) Jet Propulsion Laboratory (JPL) Land Information Systems (LIS) Low Earth Orbit (LEO) Madden Julian Oscillation (MJO) Maxwell Model 3D (NMM3D) Mean-Square Slope (MSS) Modern-Era Retrospective analysis for Research and Applications (MERRA-2) Multi-satellitE Retrievals for GPM (IMERG) National Aeronautics and Space Administration (NASA) NASA-ISRO (NISAR) National Oceanic and Atmospheric Administration (NOAA) Normalized Difference Vegetation Index (NVDI) OceanSat Scatterometer (OSCAT) Pseudo-Random Noise (PRN)Research Opportunities in Space and Earth Science (ROSES) Science Data Record (SDR) Signal-to-Noise Ratio (SNR) Soil Moisture Active Passive (SMAP) Soil Moisture Content (SMC) Soil Moisture Ocean Salinity (SMOS)Space-borne Imaging Radar-C (SIR-C)

Synthetic Aperture Radar (SAR) TechDemoSat-1 (TDS-1) Tropical Cyclone (TC) United Kingdom (UK)United Nations (UN) University Corporation for Atmospheric Research (UCAR) University of Michigan (UM) Vegetation Optical Depth (VOD) Vegetation Water Content (VWC) Visible Infrared Imaging Radiometer Suite (VIRRS) Wave-Watch 3 (WW3) Young Sea/Limited Fetch (YSLF)
