Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 14 2 2010 10.5194/hess-14-193-2010 http://www.hydrol-earth-syst-sci.net/14/193/2010/ http://www.hydrol-earth-syst-sci.net/14/193/2010/hess-14-193-2010.html http://www.hydrol-earth-syst-sci.net/14/193/2010/hess-14-193-2010.pdf 193 204 2010-02-05 Relating surface backscatter response from TRMM precipitation radar to soil moisture: results over a semi-arid region H. Stephen S. Ahmad sajjad.ahmad@unlv.edu T. C. Piechota C. Tang Department of Civil and Environmental Engineering, University of Nevada, Las Vegas, NV 89154, USA Department of Geosciences, Idaho State University, Pocatello, ID 83209, USA The Tropical Rainfall Measuring Mission (TRMM) carries aboard the Precipitation Radar (TRMMPR) that measures the backscatter (&sigma;°) of the surface. &sigma;° is sensitive to surface soil moisture and vegetation conditions. Due to sparse vegetation in arid and semi-arid regions, TRMMPR &sigma;° primarily depends on the soil water content. In this study we relate TRMMPR &sigma;° measurements to soil water content (<i>m<sub>s</sub></i>) in the Lower Colorado River Basin (LCRB). &sigma;° dependence on <i>m<sub>s</sub></i> is studied for different vegetation greenness values determined through Normalized Difference Vegetation Index (NDVI). A new model of &sigma;° that couples incidence angle, <i>m<sub>s</sub></i>, and NDVI is used to derive parameters and retrieve soil water content. The calibration and validation of this model are performed using simulated and measured <i>m<sub>s</sub></i> data. Simulated <i>m<sub>s</sub></i> is estimated using the Variable Infiltration Capacity (VIC) model and measured <i>m<sub>s</sub></i> is acquired from ground measuring stations in Walnut Gulch Experimental Watershed (WGEW). <br><br> &sigma;° model is calibrated using VIC and WGEW <i>m<sub>s</sub></i> data during 1998 and the calibrated model is used to derive <i>m<sub>s</sub></i> during later years. The temporal trends of derived <i>m<sub>s</sub></i> are consistent with VIC and WGEW <i>m<sub>s</sub></i> data with a correlation coefficient (<i>R</i>) of 0.89 and 0.74, respectively. Derived <i>m<sub>s</sub></i> is also consistent with the measured precipitation data with <i>R</i>=0.76. The gridded VIC data is used to calibrate the model at each grid point in LCRB and spatial maps of the model parameters are prepared. The model parameters are spatially coherent with the general regional topography in LCRB. 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