The aim is a study of ripples and megaripples, which are characteristic sand structures found on Earth and Mars. Our collaboration, involving geomorphologists and physicists, combine field and wind-tunnel measurements with mathematical modeling in a single coordinated effort to quantitatively understand aeolian transport mechanisms and ripple transverse instability creating these structures. In our field work at Kasuy in the southern Negev in Israel we measure surface features over time to study ripple formation and destruction while particle size distribution is analyzed in the lab. The boundary-layer stationary wind tunnel allows for the simulation and quantification of high-resolution sand processes on controlled wind conditions. The mathematical modeling is combine grain-scale numerical calculations with analytical continuum modeling for both ripples and megaripples. In particular, we propose an innovative modeling approach for megaripples, based on recent progress in the quantitative description of the complicated aeolian sand transport process. The project provide unique opportunities to gain a comprehensive understanding of the formation and (co-)evolution of ripples and megaripples, with important implications for the control of wind erosion of agricultural fields and dust emission in aridlands.