20-EPN2-094: Miniature Wind Vanes on Mars – Extracting Wind Flow Properties From Close-up Images of Sand Grains
Visit by Sebastiaan de Vet and Andreas Zafiropoulosof TU Delft (Netherlands) to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 22-26 January 2024
Report summary: Aeolian sediments are ubiquitous at the surface of Mars where they are found in active sand dunes and lithified aeolian outcrops. These features form a geological record of past and present interactions between the surface and atmosphere of an evolving planet. A deeper understanding of their formation and context can be obtained by studying these deposits at the grain-scale level. From terrestrial studies, we known that airborne orientation of non-spherical grains due to long-axis streamlining to the wind flow is considered to occur almost instantaneously after entrainment grains by saltation. Grain orientation in sediment fabrics therefore harbours valuable information on near-surface wind flow and particle mobility. A key focus of this project was to establish how atmospheric pressure and above-threshold wind conditions modulate the observed grain orientation signal. Well-rounded aeolian sand for the wind tunnel experiments was collected from the active drift sand geotope at ‘Bedafse Bergen’, located in SE Netherlands.
At the Aarhus Wind Tunnel Facility, we performed several experiments under various atmospheric pressures from ambient sea-level conditions to Mars-analogue pressures. Close-up images were obtained from the sediment fabric after various runs at 120% and 150% above threshold conditions. A date pipeline has been developed and is being refined for processing of imagery and quantifying the grain orientation to ultimately disentangle effects of airborne streamlining of grains and impact randomisation at various wind speeds and atmospheric pressures.
