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Title: PHYSICALLY BASED ESTIMATION OF BARE SURFACE SOIL MOISTURE WITH THE PASSIVE RADIOMETERS

Author
item SHI, J - UNIV. OF CA SANTA BARBARA
item JIANG, L - BEIJING NORMAL UNIVERSITY
item ZHANG, L - BEIJING NORMAL UNIVERSITY
item CHEN, K - NATL CENTRAL UNIV. TAIWAN
item WIGNERON, J - INST NATL RSCH AGRON
item CHANZY, A - INST NATL RSCH AGRON
item Jackson, Thomas

Submitted to: IEEE Transactions on Geoscience and Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2006
Publication Date: 12/1/2006
Citation: Shi, J., Jiang, L.M., Zhang, L.X., Chen, K.S., Wigneron, J.P., Chanzy, A., Jackson, T.J. 2006. Physically based estimation of bare surface soil moisture with the passive radiometers. IEEE Transactions on Geoscience and Remote Sensing. 44:3145-3153.

Interpretive Summary: An inversion model based on a parameterized surface emission model was developed in this study. It uses dual polarization measurements to minimize surface roughness effects and to estimate surface dielectric properties directly. This was done by evaluating the relationship between the surface roughness parameters at different polarizations. With this relationship, the inversion model can be derived. The retrieval model has a very simple form and avoids using the numerical technique by the least-square fitting in the inversion process that commonly results in a multi-solution problem and is computational intensive. The accuracy slightly decreases as the microwave frequency increases. Validation of this inversion technique using two sets of ground-based microwave radiometer experiment data yielded standard error of estimates of approximately 4%. These results indicate that the newly developed inversion technique offers a significant improvement for minimizing the effect of surface roughness for soil moisture estimation. It should be very useful in monitoring land surface soil moisture with the current available passive microwave sensors.

Technical Abstract: A physically based bare surface soil moisture inversion technique for application with passive microwave satellite measurements including AMSR-E, SSM/I, SSMR and TMI was developed in this study. The inversion technique is based on the concept of a simple parameterized surface emission model, the Qp model, that was developed using AIEM simulations of microwave emission. Through evaluation of the relationship between the roughness parameters Qp at different polarizations, it was found that they could be described by a linear function. Using this relationship and the surface emissivities measured from two polarizations, the effect of the surface roughness is cancelled out. In other terms, this approach consisted in adding different weights on the v and h polarization measurements so as to minimize surface roughness effects. This method leads to a dual-polarization inversion technique for the estimation of the surface dielectric properties directly from the emissivity measurements. For validation, we compared soil moisture estimates derived from ground radiometer measurements at C- to Ka-band obtained from the INRA’s field experimental data in 1993 and BARC’s field experimental data at C- and X-band obtained in 1979-1982 with the field in-situ soil moisture measurements. The accuracies (root mean square error) are better than 4% for the available experimental data at the incidence angles of 50° and 60°. The newly developed inversion technique should be very useful in monitoring global soil moisture properties using the current available satellite instruments that commonly have incidence angles between 50 and 55 degrees.