Validation of SMAP soil moisture for the SMAPVEX15 field campaign using a hyper‐resolution model. Issue 4 (13th April 2017)

• Record Type: Journal Article
• Authors: Cai, Xitian; Pan, Ming; Chaney, Nathaniel W.; Colliander, Andreas; Misra, Sidharth; Cosh, Michael H.; Crow, Wade T.; Jackson, Thomas J.; Wood, Eric F.
• Is Part Of: Water resources research. Volume 53:Issue 4(2017)
• Page Start: 3013
• Page End: 3028
• Publication Date: 2017-04-13
• Subjects: SMAP soil moisture -- land surface modeling -- HydroBlocks -- SMAPVEX15 -- high resolution -- field campaign; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2016WR019967
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Accurate global mapping of soil moisture is the goal of the Soil Moisture Active Passive (SMAP) mission, which is expected to improve the estimation of water, energy, and carbon exchanges between the land and the atmosphere. Like other satellite products, the SMAP soil moisture retrievals need to be validated, with the validation relying heavily on in situ measurements. However, a one‐to‐one comparison is ill advised due to the spatial mismatch of the large SMAP footprint (∼40 km) and the point scale in situ measurements. This study uses a recently developed hyper‐resolution land surface model—HydroBlocks—as a tool to upscale in situ soil moisture measurements for the SMAPVEX15 (SMAP Validation Experiment 2015) field campaign during 2–18 August 2015. Calibrated against in situ observation, HydroBlocks shows a satisfactory Kling‐Gupta efficiency (KGE) of 0.817 and RMSE of 0.019 m 3 /m 3 for the calibration period. These results indicate that HydroBlocks can be used to upscale in situ measurements for this site. Different from previous studies, here in situ measurements are upscaled using a land surface model without bias correction. The upscaled soil moisture is then used to evaluate SMAP (passive) soil moisture products. The comparison of the upscaled network to SMAP shows that the retrievals are generally able to capture the areal‐averaged soil moisture temporal variations. However, SMAP appears to be oversensitive to summer precipitation. We expect these findings can be used to improve the SMAP soil moisture product and thus facilitate its usage in studying the water, energy, and carbon cycles. Key Points: A hyper‐resolution land surface model, HydroBlocks, is used to represent the spatial heterogeneity of soil HydroBlocks is promising for upscaling in situ soil moisture measurements SMAP soil moisture products have high accuracy and can be used for studying the water, energy, and carbon cycles