Saltation is one of the main aeolian transport methods of sand and its physics has been studied extensively both on Mars and Earth. Most studies focused on the particle dynamics of individual particles, the determination of the saltation threshold or on describing the sediment.
This study aims to further research the effect of the aerodynamic environment, specifically the pressure and shear velocity, on the degree of preferred orientation of saltated grains in the sediment. Wind tunnel experiments at various pressures and shear velocities have shown that the fabric strength increases with increasing pressure for higher shear velocities. For lower shear velocities the same is seen at higher pressures, but at low pressures, the fabric strength is increased again. At low pressures impacting grains are thought to induce splashing, randomizing the orientation of grains in the sandbed. This effect is more pronounced at high velocities and low pressures, while at high pressures the airborne streamlining of grains while in flight has a stronger influence at higher velocities, due to the increased air density. In 70% of the experiments, the microscope images of the sediment could be used to determine the wind direction with an accuracy of 10°, if data from multiple images in the same area are combined. Individual images offer less reliable results as small-scale disturbances become more pronounced.
These findings offer a new perspective on the ongoing discussion about saltation on Mars by mapping the effects of pressure and shear velocity. Further experiments at low gravity can offer a more complete understanding of the saltation process on the red planet. In the meantime, the Object Based Image Analysis technique used in this research, offers another method of estimating the wind direction on Mars, based on microscope images taken by the rovers.