Surface soil moisture is one of the crucial variables in hydrological processes, which influences the exchange of water and energy fluxes at the land surface/atmosphere interface. Accurate estimate of the spatial and temporal variations of soil moisture is critical for numerous environmental studies. Recent technological advances in satellite remote sensing have shown that soil moisture can be measured by a variety of remote sensing techniques, each with its own strengths and weaknesses. This paper presents a comprehensive review of the progress in remote sensing of soil moisture, with focus on technique approaches for soil moisture estimation from optical, thermal, passive microwave, and active microwave measurements. The physical principles and the status of current retrieval methods are summarized. Limitations existing in current soil moisture estimation algorithms and key issues that have to be addressed in the near future are also discussed.

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Satellite remote sensing applications for surface soil moisture monitoring: A review

Status of microwave soil moisture measurements with remote sensing

http://www.remotesensing.utoledo.edu/resch/student/digimgclas/articles/evaluate.pdf

Evaluating land surface moisture conditions from the remotely sensed temperature/vegetation index measurements: An exploration with the simplified simple biosphere model

http://www.disp.uniroma2.it/earth_observation/pdf/smos-soil-moisture.pdf

Retrieving near-surface soil moisture from microwave radiometric observations: current status and future plans

Status of remote sensing algorithms for estimation of land surface state parameters

Investigations concerning microwave techniques for remote estimation of soil moisture have shown Increased interest in the study of vegetation effects on the estimates of soil moisture. This paper addresses only combinations of passive microwave and visible/infrared systems. An approach is presented whereby visible/near infrared data are used to develop corrections in the microwave soil moisture signal to account for vegetation effects. Microwave brightness temperature measurements at near nadir took angles were made with 1.4- and 5-GHz systems. Visible/infrared data were collected with the NASA NS001 Thematic Mapper Simulator and the M2S imager at the time of the microwave observations. The visible/infrared data were used to calculate Perpendicular Vegetation Index (PVI) which was then related to the change in sensitivity of the microwave measurement to surface soil moisture. It was found that effective estimation of soil moisture in the presence of vegetation can be made with L-band microwave radiometers and visible/infrared sensors when the PVI is less than 4.3. If implemented from a space platform, this technique can provide a pragmatic means of estimating moisture over many agricultural areas without the expensive necessity of collecting ground data.

Sidney W. Theis

Papers

Utilization of vegetation indices to improve microwave soil moisture estimates over agricultural lands