Integration of soil moisture remote sensing and hydrologic modeling using data assimilation

The feasibility of synthesizing distributed fields of soil moisture by the novel application of four-dimensional data assimilation (4DDA) applied in a hydrological model is explored. Six 160-km(2) push broom microwave radiome ter (PBMR) images gathered over the Walnut Gulch experimental watershed in southeast Arizona were assimilated into the Topmodel-based Land-Atmosphere Transfer Scheme (TOPLATS) using several alternative assimilation procedures . Modification of traditional assimilation methods was required to use thes e high-density PBMR observations. The images were found to contain horizont al correlations that imply length scales of several tens of kilometers, thu s allowing information to be advected beyond the area of the image. Informa tion on surface soil moisture also was assimilated into the subsurface usin g knowledge of the surface-subsurface correlation. Newtonian. nudging assim ilation procedures are preferable to other techniques because they nearly p reserve the observed patterns within the sampled region but also yield plau sible patterns in unmeasured regions and allow information to be advected i n time.