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Using Cosmic-Ray Neutron Probes in Validating Satellite Soil Moisture Products and Land Surface Models

Water Resources Laboratory of Civil Engineering Department, Middle East Technical University, 06800 Ankara, Turkey
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Water 2019, 11(7), 1362; https://doi.org/10.3390/w11071362
Received: 16 May 2019 / Revised: 18 June 2019 / Accepted: 26 June 2019 / Published: 30 June 2019
(This article belongs to the Special Issue Applications of Remote Sensing and GIS in Hydrology II)
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Abstract

Soil moisture content is one of the most important parameters of hydrological studies. Cosmic-ray neutron sensing is a promising proximal soil moisture sensing technique at intermediate scale and high temporal resolution. In this study, we validate satellite soil moisture products for the period of March 2015 and December 2018 by using several existing Cosmic Ray Neutron Probe (CRNP) stations of the COSMOS database and a CRNP station that was installed in the south part of Turkey in October 2016. Soil moisture values, which were inferred from the CRNP station in Turkey, are also validated using a time domain reflectometer (TDR) installed at the same location and soil water content values obtained from a land surface model (Noah LSM) at various depths (0.1 m, 0.3 m, 0.6 m and 1.0 m). The CRNP has a very good correlation with TDR where both measurements show consistent changes in soil moisture due to storm events. Satellite soil moisture products obtained from the Soil Moisture and Ocean Salinity (SMOS), the METOP-A/B Advanced Scatterometer (ASCAT), Soil Moisture Active Passive (SMAP), Advanced Microwave Scanning Radiometer 2 (AMSR2), Climate Change Initiative (CCI) and a global land surface model Global Land Data Assimilation System (GLDAS) are compared with the soil moisture values obtained from CRNP stations. Coefficient of determination ( r 2 ) and unbiased root mean square error (ubRMSE) are used as the statistical measures. Triple Collocation (TC) was also performed by considering soil moisture values obtained from different soil moisture products and the CRNPs. The validation results are mainly influenced by the location of the sensor and the soil moisture retrieval algorithm of satellite products. The SMAP surface product produces the highest correlations and lowest errors especially in semi-arid areas whereas the ASCAT product provides better results in vegetated areas. Both global and local land surface models’ outputs are highly compatible with the CRNP soil moisture values. View Full-Text
Keywords: Cosmic Ray Neutron Probe; land surface model; SMAP; SMOS; AMSR2; ASCAT; CCI; GLDAS Cosmic Ray Neutron Probe; land surface model; SMAP; SMOS; AMSR2; ASCAT; CCI; GLDAS
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Duygu, M.B.; Akyürek, Z. Using Cosmic-Ray Neutron Probes in Validating Satellite Soil Moisture Products and Land Surface Models. Water 2019, 11, 1362.

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