Validation of SMAP L2 passive-only soil moisture products using <i>in situ</i> measurements collected in Twente, The Netherlands

Abstract

Abstract. The Twente region in the east of the Netherlands has a network with twenty soil monitoring stations that has been utilized for validation of the Soil Moisture Active/Passive (SMAP) passive-only soil moisture products. Over the period from April 2015 until December 2018, seven stations covered by the SMAP reference pixels have fairly complete data records. Spatially distributed soil moisture simulations with the Dutch national hydrological model have been utilized for the development of upscaling functions to translate the spatial mean of point measurements to the domain of the SMAP reference pixels. The native and upscaled spatial soil moisture means have been adopted as in situ references to assess the performance of the SMAP i) Single Channel Algorithm at Horizontal Polarization (SCA-H), ii) Single Channel Algorithm at Vertical Polarization (SCA-V), and iii) Dual Channel Algorithm (DCA) soil moisture estimates. In the case of the Twente network it was found that the SCA-V soil moisture retrieved SMAP observations collected in the afternoon had the best agreement with the in situ references leading to an unbiased Root Mean Squared Error (uRMSE) of 0.059 m3 m−3. This is larger than the mission target accuracy of 0.04 m3 m−3, which can be attributed to large over- and underestimation errors (> 0.08 m3 m−3) in particular at the end of dry spells and during freezing, respectively. The strong vertical dielectric gradients associated with rapid soil freezing and wetting causes the disparity in soil depth characterized by SMAP and in situ that leads to the large mismatches. Once filtered for frozen conditions and antecedent rainfall the uRMSE improves to 0.043 m3 m−3.

Validation of Sentinel-2 (MSI) and Sentinel-3 (OLCI) Water Quality Products in Turbid Estuaries Using Fixed Monitoring Stations

“…Rearranging the sides of Eq. 11 the new updated y can be obtained as (Draper et al, 2009;van der Velde et al, 2019):…”

Application of soil moisture information for operational water management

“…Examples in the Netherlands are the Twente (Dente et al, 2012;Van der Velde, 2018; and the Raam soil moisture and tem-…”

“…Additionally, we use in situ soil moisture measurements from a monitoring network to assess whether the TFN models can describe soil moisture eld conditions. The monitoring network, operating since 2009, is maintained by the ITC faculty of the University of Twente (Dente et al, 2012;Van der Velde, 2018;. Both volumetric moisture content and soil temperature are measured at 20 locations in the Twente region.…”

“…Spatial average of daily in situ soil moisture over the Twente region at 20 cm soil depth for the years 2016, 2017, and 2018. Data are retrieved from the Twente soil moisture monitoring network maintained by ITC(Dente et al, 2012;Van der Velde, 2018;.…”