Validation of soil moisture retrieval in arid and semi-arid areas

The objective of this study is to present an approach based on the thermal inertia approach to estimate the profile of soil moisture content (SMC) in the top 1m soil column using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery.In the approach,both diurnal Land Surface Temperature (LST) difference and broadband albedo (α₀) are used to determine the spatial-temporal variation of SMC.The SMC retrieval rationale is that the high Apparent Thermal Inertia (ATI) values represent the high soil moisture contents,and the opposites are true for the low ATI values.The approach assumes that the water flux in the top 1m soil column is proportional to the difference in SMC at the surface and bottom of the soil column.The water balance equation can then be applied over the soil column,which results in the establishment of a relationship between the areal mean of SMC in the soil column and the remotely sensed surface SMC.The established SMC relationship is calibrated using the experimental data and a new soil texture classification technique based on the existing Chinese soil type classification.The SMC relationship is validated over a typical arid and semiarid area in Xinjiang.The observed soil texture data is used in the app lication of the SMC relationship.Results show that the SMC relationship has the best performance for the loam and loamy clay types of soils,as the values of estimated SMC are very much close to the Time Domain Reflectometry (TDR) observations.In comparison with the TDR observation,amarginal relative error of 2.16% is found in the estimated SMC in a subarea with the sandy type of soil1 Our result demonstrates the potential of using the established SMC relationship to map the spatial-temporal variation of SMC in the top 1m soil column using the MODIS imagery over arid and semi-arid areas.