Abstract
Soil moisture is a notably important component in various studies in water sciences, including hydrology, agriculture, and water management. To achieve extensive or global spatial coverage, satellites focusing on soil moisture observation have been launched, and many satellite products, such as SMAP and SMOS soil moisture products, have been provided. Most of these satellite observations are based on the dielectric properties of wet soil, and most soil moisture retrieval algorithms are calibrated or evaluated using in situ soil moisture. While the in situ data observed by dielectric sensors, which are the most widely used, are reported to include errors caused by the so-called “temperature effects” of these sensors, the temperature dependency of bulk soil dielectric constant has rarely been discussed on satellite data. Since both in situ dielectric measurements and satellite observations are based on the same physical variable, the dielectric constant and the dielectrically measured in situ soil moisture data are also used as ground truth, it is necessary to assess the impact of temperature effects on satellite products. In this work, we attempted to identify the existence of the temperature effects and evaluate the consequences of removing these effects on in situ and satellite soil moisture and the relationships between the brightness temperature at the soil surface and the brightness temperature provided by satellite observation. To achieve the goals of this study, we analyzed the temperature effects on surface soil moisture data provided by a SMAP mission in Oklahoma, the United States. The results show that temperature effects exist in SMAP soil moisture products in Oklahoma, and the removal of these effects will potentially improve the accuracy of these products.
Highlights
Soil moisture is widely known as one of the key factors controlling the processes of the hydrologic cycle, global energy, and water circulation [1,2]
The objectives of this work are (1) to identify the existence of the temperature effects and (2) to evaluate the impacts of the removal of these effects on in situ and satellite soil moisture and the relationships between the brightness temperature at the soil surface and the brightness temperature provided by satellite observation
All the results of this study further support the conclusion that temperature effects exist in SMAP SWC data in Oklahoma
Summary
Soil moisture is widely known as one of the key factors controlling the processes of the hydrologic cycle, global energy, and water circulation [1,2]. There are several methods to collect soil moisture estimation, such as in situ measurements, satellite remote sensing, and hydrological models. Other measured techniques have been employed recently, such as the cosmic-ray neutron probe or the global positioning system (GPS), to provide more chances for relevant studies [3,4]. Each of these suffers from some limitations [5,6,7,8,9]. In situ data are known to provide the most reliable point-scale soil moisture estimation, they face a considerable restriction on regional coverage. Large-scale spatial distribution of data is not yet available [10,11,12]
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