Wind-blown sand, or "saltation", ejects dust aerosols into the atmosphere, creates sand dunes, and erodes geological features. We present a comprehensive numerical model of steady-state saltation that, in contrast to most previous studies, can simulate saltation over mixed soils. Our model simulates the motion of saltating particles due to gravity, fluid drag, particle spin, fluid shear, and turbulence. Moreover, the model explicitly accounts for the retardation of the wind due to drag from

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... ating particles. We also developed a physically-based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results. Our numerical model is the first to reproduce measurements of the wind shear velocity at the impact threshold (i.e., the lowest shear velocity for which saltation is possible) and of the aerodynamic roughness length in saltation. It also correctly predicts a wide range of other saltation processes, including profiles of the wind speed and particle mass flux, the total height-integrated mass flux, and the size distribution of saltating particles. Indeed, our model is the first to reproduce such a wide range of experimental data. Since we use a minimum number of empirical relations, our model can be easily adapted to study saltation under a variety of physical conditions, such as saltation on other planets, saltation under water, and saltating snow. We aim to use our model to develop a physically-based parameterization of dust emission for use in climate models.