The retrieval of soil moisture information with spatially and temporally high resolution from Synthetic Aperture Radar (SAR) observations is still a challenge. By using multi-orbit Sentinel-1 C-band time series, we present a novel approach for estimating volumetric soil moisture content for agricultural areas with a temporal resolution of one to two days, based on a short-term change detection method. By applying an incidence angle normalization and a Fourier Series transformation, the effect of varying incidence angles on the backscattering signal could be reduced. As the C-band co-polarized backscattering signal is prone to vegetational changes, it is used in this study for the vegetational correction of its related backscatter ratios. The retrieving algorithm was implemented in a cloud-processing environment, enabling a potential global and scalable application. Validated against eight in-situ cosmic ray neutron probe stations across the Rur catchment (Germany) as well as six capacitance stations at the Apulian Tavoliere (Italy) site for the years 2018 to 2020, the method achieves a correlation coefficient of R of 0.63 with an unbiased Root Mean Square Error of 0.063 m³/m³.

With the upcoming L-band Synthetic Aperture Radar (SAR) satellite mission Radar Observing System for Europe L-band SAR (ROSE-L) and its integration into existing C-band satellite missions such as Sentinel-1, multi-frequency SAR observations with high temporal and spatial resolution will become available. The SARSense campaign was conducted between June and August 2019 to investigate the potential for estimating soil and plant parameters at the agricultural test site in Selhausen (Germany). It included C- and L-band air- and space-borne observations accompanied by extensive in situ soil and plant sampling as well as unmanned aerial system (UAS) based multispectral and thermal infrared measurements. In this regard, we introduce a new publicly available SAR data set and present the first analysis of C- and L-band co- and cross-polarized backscattering signals regarding their sensitivity to soil and plant parameters. Results indicate that a multi-frequency approach is relevant to disentangle soil and plant contributions to the SAR signal and to identify specific scattering mechanisms associated with the characteristics of different crop type, especially for root crops and cereals.

Against the background of a worldwide decrease in the number of gauging stations, the estimation of river discharge using spaceborne data is crucial for hydrological research, river monitoring, and water resource management. Based on the at-many-stations hydraulic geometry (AMHG) concept, a novel approach is introduced for estimating river discharge using Sentinel-1 time series within an automated workflow. By using a novel decile thresholding method, no a priori knowledge of the AMHG function or proxy is used, as proposed in previous literature. With a relative root mean square error (RRMSE) of 19.5% for the whole period and a RRMSE of 15.8% considering only dry seasons, our method is a significant improvement relative to the optimized AMHG method, achieving 38.5% and 34.5%, respectively. As the novel approach is embedded into an automated workflow, it enables a global application for river discharge estimation using solely remote sensing data. Starting with the mapping of river reaches, which have large differences in river width over the year, continuous river width time series are created using high-resolution and weather-independent SAR imaging. It is applied on a 28 km long section of the Mekong River near Vientiane, Laos, for the period from 2015 to 2018.

Water plays a crucial role in food security. Currently, agriculture irrigation withdraws about 70% of the world’s fresh water. By 2050, the world population is estimated to increase to over 9 billion (UNDP, 2022). Together with climate change that is increasingly affecting the terrestrial ecosystem such as increasing the temperature, drought and extreme flood, all of which can lead to crop failure (IPCC et al., 2007) and water scarcity, the demand for food and irrigation water is expected to rise, dramatically. Accordingly, novel technologies for innovative, real-time water management for sustainable irrigation are necessary. In this regard, the main objective of this study is to simulate and predict the soil water content at the root zone, as a main factor of defining the irrigation time and quantity. Here, we have chosen a study area of 150km2 which is located in west Europe, covering parts of Netherlands, Belgium, Luxemburg and west of Germany. Therewith, we have relied on the coupled land surface-subsurface CLM-Parflow model for hydrological simulations and the soil moisture data from on-site Cosmic-ray neutron sensor (CRNS) stations, as well as the SMAP (L3_SM_E_P), and high resolution C- and L-band Synthetic Aperture Radar (SAR) are used for data assessment. It is expected that the reliability of the soil moisture magnitude and dynamic will be examined.

With the upcoming L-band Synthetic Aperture Radar (SAR) satellite mission Radar Observing System for Europe at L-band (ROSE-L) and its combination with existing C-band satellite missions such as Sentinel-1, multi-frequency SAR observations with high temporal and spatial resolution will become available. To investigate the potential for estimating soil and plant parameters, the SARSense campaign was conducted between June and August 2019 at the agricultural test site Selhausen in Germany. In this regard, we introduce a new publicly available, extensive SAR dataset and present a first analysis of C- and L-band co- and cross-polarized backscattering signals regarding their sensitivity to soil and plant parameters. The analysis includes C- and L-band airborne recordings as well as Senitnel-1 and ALOS-2 acquisitions, accompanied by in-situ soil moisture measurements and plant samplings. In addition, soil moisture was measured using cosmic-ray neutron sensing as well as unmanned aerial system (UAS) based multispectral and temperature measurements were taken during the campaign period. First analysis of the dataset revealed, that due to misalignments of corner reflectors during the SAR acquisition, temporal consistency of airborne SAR data is not given. In this regard, a scene-based, spatial analysis of backscatter behaviour from airborne SAR data was conducted, while the spaceborne SAR data enabled the analysis of temporal changes in backscatter behaviour. Focusing on root crops with radial canopy structure (sugar beet and potato) and cereal crops with elongated canopy structure (wheat, barley), the lowest correlations can be observed between backscattering signal and soil moisture, with R² values ranging below 0.35 at C-band and below 0.36 at L-band. Higher correlations can be observed focusing on vegetation water content, with R² values ranging between 0.12 and 0.64 at C-band and 0.06 and 0.64 at L-band. Regarding plant height, at C-band higher correlations with R² up to 0.55 can be seen compared to R² up to 0.36 at L-band. Looking at the individual agricultural corps in more detail, in almost all cases, the backscatter signals of C- and L-band contain a different amount of information about the soil and plant parameters, indicating that a multi-frequency approach is envisaged to disentangle soil and plant contributions to the signal and to identify specific scattering mechanisms related to the crop type, especially related to the different characteristics of root crops and cereals.

In December 2023, the Helmholtz SynCom (Synthesis and Communication) traveled to Brussels with a delegation of selected scientists from the seven Helmholtz Earth and Environment Centres. This visit aimed at sharing current research findings and exchanging ideas with members of the European Parliament and other key stakeholders. The agenda included meetings with various entities such as the European Commission’s Directorate-General for Defence Industry and Space (DG DEFIS), the Directorate-General for Climate Action (DG CLIMA), the European Space Agency (ESA), and members of the European Parliament Niklas Nienaß and Jutta Paulus. This trip proved to be a valuable opportunity to connect European environmental and climate policy with fundamental research. When communicating scientific research, the importance of selecting a format suitable for the targeted audience constituted a key point. We discuss the lessons learned, and needs for user-oriented innovative tools for public outreach and for supporting policy decisions. Our exchanges also covered the potential impact of ongoing and upcoming European projects, like satellite-based Earth Observation missions and Digital Twins of the Earth, in providing crucial data for science-backed regulations. Lastly, we address the challenges faced in policymaking and the hurdles in integrating scientific discoveries into political decisions: we report suggested possibilities of including policy makers or the consideration of current regulatory questions within research projects.