Abstract
Soil moisture is an essential variable in many hydrological and meteorological models. Spatially continuous soil moisture datasets are important for understanding water cycle and climate change. Currently, satellite-based microwave sensors have been the main resources for obtaining global soil moisture data. This paper evaluates the performance of different soil moisture products from the combined Essential Climate Variable (ECV) and Soil Moisture and Ocean Salinity (SMOS) satellite against the stations within the OzNet soil moisture networks over southeastern Australia. SMOS soil moisture products obtained from two versions (ascending and descending) were included. The evaluations were carried out at both network and site scales. According to the validation results, the ECV products outperformed the SMOS products at both scales. Comparing the two versions of the SMOS products, the SMOS ascending product generally performed better than the SMOS descending product and obtained comparable accuracy to the ECV product at Kyeamba and Yanco sites. However, the SMOS ascending performed poorly at the Adelong sites. Moreover, the ECV product has less data gaps than the SMOS products, because the ECV products were developed by combining passive and active microwave products. Consequently, the results in this study show that the combined ECV product is recommended, as both accuracy and integrity of the soil moisture product are important. The SMOS ascending product is recommended between the two overpass versions of SMOS products.
Highlights
Soil water is a key variable in the global water cycle, and is a significant medium for energy exchange between the surface of the land and the atmosphere [1,2,3,4]
To compare the performance of the three satellite-based soil moisture products, we firstly evaluated them at six selected sites (A1, A2, K3, K14, Y6, and Y9), which were randomly selected from two sites within each network
The Rano values at A1 and A2 are higher for the Essential Climate Variable (ECV) product than those of either Soil Moisture and Ocean Salinity (SMOS) products, whereas the root mean square error (RMSE) and unbiased root mean square difference (ubRMSD) for the soil moisture anomalies are lower for the ECV product than those of the SMOS products
Summary
Soil water is a key variable in the global water cycle, and is a significant medium for energy exchange between the surface of the land and the atmosphere [1,2,3,4]. The soil moisture content is the quantity of water contained in soil It can be measured on a volumetric or mass (gravimetric) basis. The water mass is the difference between the weights of the wet and oven dried samples [8] This method is time-consuming, and acquiring near-real-time soil moisture information is impossible in this way. Ground-penetrating sensors are most frequently made with resistance block sensors, tensiometers, heat dissipation sensors, neutron probes, time-domain reflectometers (TDR), frequency-domain reflectometers (FDR), and capacitance [9]. These in situ sensors can continuously monitor the soil water content automatically, and are often used to monitor soil moisture continuously in agricultural and hydrological applications. Widespread and spatially continuous measurement of soil moisture is essential, but this capability does not exist for field site measurements
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