National Aeronautics and Space Administration Jet Propulsion Laboratory
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Aug 8 Validation and Scaling of Soil Moisture in a Semi-Arid Environment: SMAP Validation Experiment 2015 (SMAPVEX 15) (Andreas Colliander) PALS Soil Moisture Retrievals Aug 16 (left) Soil moisture distribution on two days during SMAPVEX 15 as measured by PALS (Passive Active L-band Sensor). Note the high heterogeneity and variability caused by the convective precipitation cells characteristic to the North American Monsoon. The black rectangle denotes SMAP 36 -km validation pixel. (right) PALS soil moisture validation results at 3 -km resolution. The outliers are explained by the differences in soil moisture detection by in situ probes at 5 -cm depth and by the microwaves at varying depth; note that this known problem is severely exacerbated by the high spatial heterogeneity and variability during the experiment. Problem: Curbing the measurement uncertainties when validating surface soil moisture products under conditions of high spatial heterogeneity and variability is a significant challenge affecting the validation of satellite based soil moisture products. The SMAP mission executed a field experiment in southern Arizona in 2015 during the North American Monsoon, which guaranteed highly heterogeneous and varying soil moisture conditions. Finding: It was found that when accounting for the uncertainties in the in situ measurements caused by the heterogeneous and varying conditions the performance metrics of soil moisture retrievals improve significantly. The vertical dimension in soil moisture variability proved to be similarly important as the spatial distribution in capturing the highly dynamic soil moisture conditions. Significance: A significant caveat needs to be associated with soil moisture performance metrics determined under highly heterogeneous and varying conditions until the conditions are accounted for in the measurement strategy of the reference value. This will result in more reliable soil moisture products which means better flood prediction, drought monitoring, food security applications, weather forecasting, and climate modeling. Colliander, A. , M. H. Cosh, S. Misra, T. J. Jackson, W. T. Crow, S. Chan, R. Bindlish, C-S. Chae, C. Holifield Collins, S. Yueh (2017). Validation and Scaling of Soil Moisture in a Semi-Arid Environment: SMAP Validation Experiment 2015 (SMAPVEX 15), Remote Sensing of Environment, 196, 101 -112. 1
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