Abstract
An ensemble method was used to combine three surface soil moisture products, retrieved from passive microwave remote sensing data, to reconstruct a monthly soil moisture data set for China between 2003 and 2010. Using the ensemble data set, the temporal and spatial variations of surface soil moisture were analyzed. The major findings were: (1) The ensemble data set was able to provide more realistic soil moisture information than individual remote sensing products; (2) during the study period, the soil moisture increased in semiarid regions and decreased in arid regions with anoverall drying trend for the whole country; (3) the soil moisture variation trends derived from the three retrieval products and the ensemble data differ from each other but all data sets show the dominant drying trend for the summer, and that most of the drying regions were in major agricultural areas; (4) compared with the precipitation trends derived from Global Precipitation Climatology Project data, it is speculated that climate change is a possible cause for the drying trend in semiarid regions and the wetting trend in arid regions; and (5) combining soil moisture trends with land surface temperature trends derived from Moderate Resolution Imaging Spectroradiomete, the study domain was divided into four categories. Regions with drying and warming trends cover 33.2%, the regions with drying and cooling trends cover 27.4%, the regions with wetting and warming trends cover 21.1% and the regions with wetting and cooling trends cover 18.1%. The first two categories primarily cover the major grain producing areas, while the third category primarily covers nonarable areas such as Northwest China and Tibet. This implies that the moisture and heat variation trends in China are unfavorable to sustainable development and ecology conservation.
Highlights
Advanced Microwave Scanning Radiometers for EOS (AMSR-E) was launched onboard the Aqua satellite by the National Aeronautics and Space Administration (NASA) in May 2002 and has many advantages compared with former passive radiometers, such as Scanning Multichannel Microwave Radiometer (SMMR) [6] and Special Sensor Microwave Imager (SSM/I) [7]
Some agencies have developed AMSR-E soil moisture products, such as the single channel retrieving products by the United States Department of Agriculture [9], and the regression products by the Institute of Applied Physics of the Italian National Research Council [10]. These products were focused on specific case studies and not operationally updated, only the NASA, Japan Aerospace Exploration Agency (JAXA) and Vrije Universiteit in Amsterdam (VUA) soil moisture products were used in this study
This study developed a multiproduct ensemble method to combine the JAXA, NASA and VUA AMSR-E products and the new ensemble data set was used to analyze the temporal and spatial characteristics of surface soil moisture in China
Summary
AMSR-E was launched onboard the Aqua satellite by the National Aeronautics and Space Administration (NASA) in May 2002 and has many advantages compared with former passive radiometers, such as Scanning Multichannel Microwave Radiometer (SMMR) [6] and Special Sensor Microwave Imager (SSM/I) [7]. NASA, Vrije Universiteit in Amsterdam (VUA) and the Japan Aerospace Exploration Agency (JAXA) operationally release global soil moisture retrievals from AMSR-E Besides these three institutes, some agencies have developed AMSR-E soil moisture products, such as the single channel retrieving products by the United States Department of Agriculture [9], and the regression products by the Institute of Applied Physics of the Italian National Research Council [10]. Some agencies have developed AMSR-E soil moisture products, such as the single channel retrieving products by the United States Department of Agriculture [9], and the regression products by the Institute of Applied Physics of the Italian National Research Council [10] These products were focused on specific case studies and not operationally updated, only the NASA, JAXA and VUA soil moisture products were used in this study. The VUA product covers the period from 2003 to 2009 and the JAXA and NASA products cover the period from 2003 to 2010
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