Conventionally, Global Navigation Satellite System – Reflectometry (GNSS-R) has been implemented to capture the reflection of a Global Positioning System (GPS) signal in its most probable polarization. Since GPS signals are transmitted with right-hand circular polarization (RHCP), the reflected signal is expected to arrive primarily in left-hand circular polarization (LHCP). Consequently, missions like TechDemoSat-1, which was decommissioned in 2019, and CYGNSS, operational from August 2018 to the present, were both designed to capture the L1 GPS signals (1575.42 MHz) in LHCP. CYGNSS provides unique revisit times thanks to its constellation of 7 satellites, each capable of measuring up to 4 GPS satellites simultaneously. While the CYGNSS mission was originally developed to improve our understanding of cyclone formation and dynamics by estimating wind speeds over oceans, the measurements extend to land and are also sensitive to land variables such as soil moisture, surface roughness, vegetation characteristics, and the presence of water bodies. Over land, the variability of scenarios makes GPS signal scattering intricate and rich in information, with links to roughness and vegetation that can be directly connected to polarimetric signatures.

Currently, there is one mission that provides polarimetric GNSS-R measurements: the Soil Moisture Active Passive (SMAP) mission. SMAP carries a radar whose receiver was modified to enable the reception of L2C GPS signals (1227.60 MHz) following a radar transmitter anomaly. The SMAP-R system receives signals through linearly polarized antennas, allowing for the reconstruction of the full Stokes parameters to describe the Earth’s surface polarimetric scattering. SMAP-R data, spanning from 2015 to the present, has shown sensitivity to geophysical variations even under very dense vegetation. In the future, the European Space Agency’s (ESA) HydroGNSS mission will be launched with dual-polarization capabilities.

This presentation will introduce the SMAP-R dataset to the scientific community, highlighting the main sensitivities of full-polarimetric GNSS-R measurements to the Earth’s surface geophysical parameters and the potential applications enabled by upcoming polarimetric GNSS-R missions.

About the Speaker

Nereida Rodriguez-Alvarez (Senior Member, IEEE) received the B.Sc. and M.Sc. degrees in telecommunications and the Ph.D. degree in remote sensing from the Universitat Politècnica de Catalunya, Barcelona, Spain, in 2005, 2007, and 2011, respectively. She has collaborated with the National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA; the Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA; and Purdue University, West Lafayette, IN, USA, as a Post-Doctoral Researcher. She was a member of the Cyclone Global Navigation Satellite System (CYGNSS) Science Team for three years. She specializes in bistatic radar techniques for Earth sensing using signals of opportunity, specifically through Global Navigation Satellite System-Reflectometry (GNSS-R), and has contributed to the retrieval of land geophysical parameters and ocean surface winds. Nereida joined the Jet Propulsion Laboratory (JPL) in January 2018 as part of the Planetary Radar and Radio Science group. During her time at JPL, she has been involved in both Earth science and planetary radar projects. Regarding her Earth science contributions, Nereida has led scientific research for a JPL Research and Technology Development project focused on using opportunistic GPS reflections from CYGNSS, TDS-1, and the SMAP radar receiver to sense wetlands, polar sea ice, and freeze/thaw states. She has also explored other applications of GNSS-R, such as crop growth monitoring and flood detection/monitoring strategies in urban and agricultural areas. In 2019, Nereida received the NASA Early Career Public Achievement Medal for “the analysis of bistatic radar signals, resulting in major advancements in our understanding of Earth, including wetlands, sea ice, and floods.” In 2021, she was awarded the Charles Elachi Award for “outstanding contributions and exceptional ability in using bistatic radar as an innovative tool for studying Earth’s geophysical processes.” Nereida also secured a SMAP Science Team NASA ROSES proposal, becoming part of the SMAP Science Team and leading the efforts to process and calibrate the bistatic radar dataset collected from the SMAP radar receiver, making it the first spaceborne full polarimetric GNSS-R instrument and obtaining a JPL Voyager Award and JPL Team Award. Under this project, Nereida and her team have highlighted the advantages of polarimetric GNSS-R and provided insights into upcoming polarimetric GNSS-R missions. Additionally, on the planetary side, she has engaged in the Deep Space Network’s (DSN) Goldstone Solar System Radar (GSSR) signal processing activities. Currently, Nereida continues to explore GNSS-R and polarimetric GNSS-R applications in Earth science while expanding her knowledge to planetary science, studying the properties of solar system bodies.