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This study assessed the performance of different remotely sensed soil moisture products with in situ observations; six profile probes for the water content monitoring were selected, operating during 2016–2021 from the Voineşti Experimental Basin in the Romanian Subcarpathian region. The reliability of satellite observations has been analyzed on both single ground-based observation points and spatialized information, considering near-surface and root-zone soil moisture data. The physics-based index (HCI) and some statistical tests widely used in inter-comparison analyses have been computed. The study of HCI highlighted that the SMAP SP_L4_SM products have shown the best performances considering the near-surface and root-zone data evaluations. The comparison of SWI1km observations with in situ data produced good results for single-point and spatialized soil moisture estimations acquired at different depths over the experimental basin. The SSM1km and SMAP L2_SM_SP products exhibited the lowest performances. The results contribute to the validation of satellite products of surface and root-zone soil moisture in the Subcarpathian region, helping to provide information in an area not monitored by the International Soil Moisture Network. The findings offer valuable insights into evaluating the performance of satellite soil moisture products in the Romanian region. [ABSTRACT FROM AUTHOR]

The roadmap to enable operational soil moisture (SM) monitoring for meteorologic and hydrological early warning is challenged by the uncertainty within the available remote sensing and modelling products. This study addressed two relevant uncertainties: the residual trends in the series and the spatial consistency. While the latter has been often revisited to validate remote sensing and modelling products against in-situ data, the former is often disregarded in studies addressing SM changes. This study evaluated three SM products: (1) the Satellite Application Facility on Support to Operational Hydrology and Water Management (H SAF) active Advanced SCATterometer (ASCAT)-derived dataset, (2) the passive subset of the European Space Agency (ESA) - Climate Change Initiative (CCIp), and (3) the modelled dataset from the European Drought Observatory (EDO). The analysis was carried out over Europe in the period 2007–2022 at 10-day temporal scales. We obtained that even these popular datasets are subject to patches of spatial inconsistency and residual trends when compared to the in-situ data from the International Soil Moisture Network (ISMN). In view of the great complementarity shown by the active and passive remote sensing and the modelled SM estimates, two merged products are proposed and tested against in-situ data. Results indicate that combining H SAF ASCAT, CCIp and EDO equals or surpasses the spatial and temporal consistency of the individual SM products alone, even when only the near-real-time products of H SAF ASCAT and EDO are combined. Thus, merging remote sensing and modelled SM products is advantageous for enhanced spatial and temporal operational monitoring of SM at the European scale. [ABSTRACT FROM AUTHOR]