Validation of Smos L2 and L3 Soil Moisture Products Over the Duero Basin at Different Spatial Scales

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 km<sup>2</sup>), which provide multiple ground measurements within a single satellite footprint, and large-scale (>10000 km<sup>2</sup>), 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 km<sup>2</sup>). 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 km<sup>2</sup>). 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.

Comparison of Satellite Soil Moisture Products in Mongolia and Their Relation to Grassland Condition

“…Particularly, in the early spring and late autumn, the greatest variations of soil moisture were observed in both datasets. The SMOS data exhibited a certain underestimation in April and October compared to the ground observations, although the SMOS data reacted to rainfall events more quickly (Figures 4 and 5), which was also detected in previous validation experiments [51].…”

Global-scale evaluation of SMAP, SMOS and ASCAT soil moisture products using triple collocation

“…However, difficulty in obtaining viable estimates of ground truth soil moisture at the satellite footprint scale has limited past validation activities to a small number of locations (e.g., SMAP's core validation sites) and/or discrete time periods (e.g., field campaigns). The broader evaluation of satellite soil moisture products (across regional or continental scales) is typically based on comparisons with sparse ground soil moisture networks or modeled datasets (e.g., Paulik et al 2014;González-Zamora et al 2015;Al-Yaari et al 2014;Polcher et al 2016;Kim et al 2018). Naturally, such comparisons are unable to provide direct validation metrics relative to the ground truth, but rather metrics against a chosen reference dataset with unknown errors at the footprintscale of satellite retrievals.…”

Inter-comparison of SMOS and AMSR-E soil moisture products during flood years (2010–2011) over Pakistan

“…Overall, the years 2010-2011 were intensive monsoon period followed by destructive floods. Soil moisture estimates from SMOS in monsoon months were generally higher as compare to AMSR-E, and it was assumed that precipitation is the probable reason of this overestimation as mentioned also in many earlier studies that SMOS is much more sensitive to rainfall events (Gherboudj et al, 2012;González-Zamora et al, 2015;Jackson et al, 2012;Leroux, Kerr, Al Bitar et al, 2014).…”