Xingming　Zheng　,　Member,　IEEE,　Zhuangzhuang　Feng,　Hongxin　Xu,　Yanlong　Sun,　Yu　Bai,　Bingze　Li,　Lei　Li,Xiaowei　Zhao,　Rui　Zhang,　Tao　Jiang,　Member,　IEEE,　Xiaojie　Li,　and　Xiaofeng　Li,　Member,　IEEE 

Abstract：

Passive　microwave　remote　sensing　is　an　effective　way　to　obtain　global　soil　moisture　(SM)　measurements,　and　many　studies　have　explored　the　uncertainty　inherent　in　microwave-based　SM　products.　However,　SM　product　accuracy　has　not　been　evaluated　in　northeast　China,　a　national　and　global　production　base　for　commoditygrain.Inthisstudy,aground-basedwirelesssensornetwork　with　28　observation　nodes　that　were　spatially　distributed　within　36　×　36　km　was　established　to　achieve　satellite-scale　“true”　SM　values　through　sensor　calibration　for　specific　soil　types,　senor　consistencytesting,andspatialscaletransformation.Theuncertainties　of　four　passive　microwave　SM　products　(SMAP　L3,　SMOS　L3,　the　Japan　Aerospace　Exploration　Agency/JAXA　AMSR2,　and　FY3C)　were　investigated　and　the　following　conclusions　were　obtained:　1)　SMAP　SM　accuracy　was　very　close　to　the　expected　application　accuracy　of　0.04　cm3/cm3,　followed　by　SMOS,　FY3C,　and　AMSR2;　2)forSMOSandSMAP,therewerenosignificanttemporalchanges　in　SM　errors,　except　for　the　larger　error　of　descending　SMOS　SM　and　June　SM　values　for　descending　SMAP　and　ascending　SMOS.　AMSR2　SM　generally　underestimated　field　SM,　while　FY3C　SM　values　under　low　vegetation　conditions　were　more　consistent　with　field　data,　with　an　error　of　about　0.06　cm3/cm3;　3)　agricultural　activities　and　rainfall　caused　the　soil　surface　roughness　to　increase　or　decrease　within　a　growing　season,　which　may　have　been　an　important　source　of　satellite-scale　SM　error　indicated　by　high　bias　values　in　July　for　both　SMAP　and　SMOS;　and　4)　the　standard　deviation　of　field　SM　(0.06　cm3/cm3)　produced　a　SMAP　SM　error　of　about　0.06　cm3/cm3　in　low　vegetation　water　content　conditions,　indicating　that　SM　spatial　heterogeneity　cannot　be　ignored　in　the　retrieval　algorithm.　This　article　investigated　the　accuracy　and　error　sources　of　four　satellite　SM　products　in　the　farmland　area　of　northeast　China,　and　identified　future　research　directions　for　further　improving　SM　algorithms.　

Index　Terms：China,　farmland,　passive　microwave　remote　sensing,　soil　moisture　(SM),　validation.

Links to the paper：https://ieeexplore.ieee.org/document/9096583