## 3 Operational Retrievals of SSM from EO
An example of operational product from the ESA's SMOS satellite is shown in Figure 3.  
In the near future, higher resolution (<1 km) soil moisture products are expected to become available based on the SAR sensor on-board Sentinel-1 (e.g., [58; 59; 60; 61]) as well as from advanced disaggregation approaches (see review by [62]). Further details of the existing operational SSM products are provided in Table 2.  
Soil moisture was recognised by the Global Climate Observing System to be an essential climate variable in 2010. This underscores the potential of the above-mentioned data sets to support climate studies and, in a broader context, the interest in the operational estimation of satellite soil moisture. The ESA Climate Change Initiative (CCI) is one of the first initiatives to merge the different satellite microwave products available into a temporally and spatially consistent data set [57; 63]. It is currently providing a multi-decadal soil moisture observational data record that covers partially the last 37 years and is expected to progressively incorporate latest satellite soil moisture products, reaching NRT capabilities by next year [60]. Note that, long-term soil moisture datasets are needed for climate studies and also to undertake robust assessments of the impact of using EO-based soil moisture estimates in Earth Science applications. Continuity of observational records of surface soil moisture is ensured by the new generations of C-band radiometers (on-board GCOM-W2, GCOM-W3) and C-band scatterometers (on-board MetOp-C, MetOp-SG) and by new mission concepts at L-band, such as the Water Cycle Observation Mission (WCOM) from the Chinese Academy of Sciences, the US and Indian NASA-Indian Space Research Organization Synthetic Aperture Radar (NISAR) and the Argentinian Satelite Argentino de Observacion Con Microondas (SAOCOM). Figure 3: An example of the SMOS L4 disaggregated product over the Iberian Peninsula from November 4, 2010, SMOS afternoon pass. First two rows contain images of Landsat RGB composite (**left**), SMOS L2 soil moisture (**centre**) and SMOS data disaggregated at 1 km (**right**) (first row) and REMEDHUS (second row), The layout of permanent stations within REMEDHUS is overlaid to the Landsat composite. The third row contains the MODIS/Terra NDVI (**left**), SMOS L1C horizontal T\({}_{\text{B}}\) at 42.5 (**centre**) and MODIS/Terra LST (**right**) from the same day, used to generate the soil moisture map at 1 km. Figure adopted from [55]. The main benefit of EO soil moisture data is its spatio-temporal coverage and its relatively lower cost for large scale applications as compared to in-situ or airborne acquisitions. The accuracy of the satellite microwave SSM products has been demonstrated in a number of validation studies comparing satellite retrievals with in-situ observations and/or outputs of land surface/hydrological models [61; 64; 65; 66]. Also, the number of applications already using these products has grown in the last years, providing an indirect assessment of their quality. In this regard, a broad and non-exhaustive list of applications that will potentially benefit from the use of satellite soil moisture information includes hydrology [67; 68; 69], meteorology [70; 71] and water resource management [72; 73]. The reader is referred to [74] for a comprehensive review of operational applications using satellite soil moisture retrievals. The rest of this section presents sample research studies with focus on the use of soil moisture data on agro-ecology and water management related applications. Agriculture and Agri-Food Canada (AAFC) has developed a system to integrate multi-sensor soil moisture data (through data intercalibration), therefore allowing the seamless use of AMSR, SMOS and SMAP for agroclimate risk monitoring and reporting [75]. The feasibility of detecting vegetation drought with ASCAT-derived soil moisture was reported in a recent study [76]. Agricultural drought indices based on SMOS soil moisture information have also been developed [77; 78].