Abstract
Abstract. An increasing number of permanent soil moisture measurement networks are nowadays providing the means for validating new remotely sensed soil moisture estimates such as those provided by the ESA’s Soil Moisture and Ocean Salinity (SMOS) mission. Two types of in situ measurement networks can be found: small-scale (100–10000 km2), which provide multiple ground measurements within a single satellite footprint, and large-scale (>10000 km2), which contain a single point observation per satellite footprint. This work presents the results of a comprehensive spatial and temporal validation of a long-term (January, 2010 to June, 2014) dataset of SMOS-derived soil moisture estimates using two in situ networks within the Duero basin (Spain). The first one is the Soil Moisture Measurement Stations Network of the University of Salamanca (REMEDHUS), which has been extensively applied for validation of soil moisture remote sensing observations, including SMOS. REMEDHUS can be considered within the small-scale network group (1300 km2). The other network started from an existing meteorological network from the Castilla y León region, where soil moisture probes were incorporated in 2012. This network can be considered within the large-scale group (65000 km2). Results from comparison to in situ show that the new reprocessed L2 product (v5.51) improves the accuracy of former soil moisture retrievals, making them suitable for developing new L3 products. Validation based on comparisons between dense/sparse networks showed that temporal patterns on soil moisture are well reproduced, whereas spatial patterns are difficult to depict given the different spatial representativeness of ground and satellite observations.
Highlights
The World Meteorological Organization (WMO), the Global Climate Observing System and the Committee on Earth Observation Satellites included soil moisture as one of the Essential Climate Variables (WMO, 2010), highlighting its importance in meteorology and climatology, taking a central role in the land surface-atmosphere interface, and in the interactions between soil, vegetation and climate forcing
Validation based on comparisons between dense/sparse networks showed that temporal patterns on soil moisture are well reproduced, whereas spatial patterns are difficult to depict given the different spatial representativeness of ground and satellite observations
The Soil Moisture and Ocean Salinity (SMOS) dataset followed the temporal dynamics of the REMEDHUS dataset, a slight underestimation can be observed, in the dry periods
Summary
The World Meteorological Organization (WMO), the Global Climate Observing System and the Committee on Earth Observation Satellites included soil moisture as one of the Essential Climate Variables (WMO, 2010), highlighting its importance in meteorology and climatology, taking a central role in the land surface-atmosphere interface, and in the interactions between soil, vegetation and climate forcing. A third instrument, Aquarius, was launched in June 2011 on board the international Aquarius/SAC-D mission by NASA and Argentina's space to primarily measure sea surface salinity This mission is providing soil moisture products (Lagerloef et al, 2008)
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