Abstract
Soil moisture products acquired from passive satellite missions have been widely applied in environmental processes. A primary challenge for the use of soil moisture products from passive sensors is their reliability. It is crucial to evaluate the reliability of those products before they can be routinely used at a global scale. In this paper, we evaluated the Soil Moisture Active/Passive (SMAP) and the Advanced Microwave Scanning Radiometer (AMSR2) radiometer soil moisture products against in situ measurements collected from American networks with four statistics, including the mean difference (MD), the root mean squared difference (RMSD), the unbiased root mean square error (ubRMSE) and the correlation coefficient (R). The evaluation results of SMAP and AMSR2 soil moisture products were compared. Moreover, the triple collocation (TC) error model was used to assess the error among AMSR2, SMAP and in situ data. The monthly average and daily AMSR2 and SMAP soil moisture data were analyzed. Different spatial series, temporal series and combined spatial-temporal analysis were carried out. The results reveal that SMAP soil moisture retrievals are generally better than AMSR2 soil moisture data. The remotely sensed retrievals show the best agreement with in situ measurements over the central Great Plains and cultivated crops throughout the year. In particular, SMAP soil moisture data shows a stable pattern for capturing the spatial distribution of surface soil moisture. Further studies are required for better understanding the SMAP soil moisture product.
Highlights
Zeng et al [29] carried out a preliminary evaluation of the Soil Moisture Active/Passive (SMAP) radiometer soil moisture product against in situ measurements collected from different networks that cover different climatic and land surface conditions, and the results show that the SMAP soil moisture product is in good agreement with the in situ measurements, it exhibits dry or wet bias at different network regions
The results showed that the correlation of SMAP level 4 soil moisture (L4 SM) data with in situ soil moisture data for all investigated land cover types, except Grass/Herbaceous, were
The results showed that the correlation of SMAP L4 SM data with in situ soil moisture data for all investigated land cover types, except Grass/Herbaceous, were generally bad over the period from July to October
Summary
Mission, the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E)and. Advanced Microwave Scanning Radiometer 2 (AMSR2) mission [4,5,6,7,8]. Soil moisture data sets acquired from all of these passive missions are widely used. 2017, 9, 104 used for different satellite data, the quality and continuity of passive microwave soil moisture products varies in space and time [9,10,11]. Several studies have evaluated soil moisture products based on passive microwave sensors against in situ measurements over different regions [12,13,14,15]. Quality evaluations for other soil moisture products, such as the AMSR-E, Aquarius, European Space Agency Climate Change Initiative (ESA CCI), and ERA-Interim soil moisture products produced by the Centre for Medium-Range
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