[1] Three-dimensional particle image velocimetry (3D PIV) applied to impact cratering experiments allows the direct measurement of ejecta particle positions and velocities within the ejecta curtain as the crater grows. Laboratory experiments were performed at the NASA Ames Vertical Gun Range with impact velocities near 1 km/s (6.35-mm diameter aluminum spheres) into a medium-grained (0.5 mm) particulate sand target in a vacuum at 90°and 30°from the horizontal. This study examines the first 50% of crater growth, during which the crater has grown to one half its final radius. From the 3D PIV data, the ballistic trajectories of the ejecta particles are extrapolated back to the target surface to determine ejection velocities, angles, and positions. For vertical impacts these ejection parameters remain constant in all directions (azimuths) around the crater center. The 30°impacts exhibit asymmetries with respect to azimuth that persist well into the excavation-stage flow. These asymmetries indicate that a single stationary point source is not adequate to describe the subsurface flow field during an oblique impact. INDEX TERMS:5420 Planetology: Solid Surface Planets: Impact phenomena (includes cratering); 5494 Planetology: Solid Surface Planets: Instruments and techniques; KEYWORDS: Oblique impacts, ejecta flow, particle image velocimetry, Ames Vertical Gun Range, experimental impacts Citation: Anderson, J. L. B., P. H. Schultz, and J. T. Heineck, Asymmetry of ejecta flow during oblique impacts using threedimensional particle image velocimetry,

Experimental ejection angles for oblique impacts:Implications for the subsurface flow-field Abstract-A simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times. A specific example of such an analytical solution is Maxwell's Z-Model, which is based on a point-source assumption. Here, the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the NASA Ames Vertical Gun Range. Data from experiments reveal that impacts at angles as high as 45° to the target's surface generate subsurface flow-fields that are significantly different from those created by vertical impacts. The initial momentum of the projectile induces a subsurface momentum-driven flow-field that evolves in three dimensions of space and in time to an excavation flow-field during both vertical and oblique impacts. A single, stationary pointsource model (specifically Maxwell's Z-Model), however, is found inadequate to explain this detailed evolution of the subsurface flow-field during oblique impacts. Because 45° is the most likely impact angle on planetary surfaces, a new analytical model based on a migrating point-source could prove quite useful. Such a model must address the effects of the subsurface flow-field evolution on crater excavation, ejecta deposition, and transient crater morphometry.

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This article describes the development and use of Background Oriented Schlieren on a full-scale supersonic jet in flight. A series of flight tests was performed in October, 2014 and February 2015 using the flora of the desert floor in the Supersonic Flight Corridor on the Edwards Air Force Base as a background. Flight planning was designed based on the camera resolution, the mean size and color of the predominant plants, and the navigation and coordination of two aircraft. Software used to process the image data was improved with additional utilities. The planning proved to be effective and the vast majority of the passes of the target aircraft were successfully recorded. Results were obtained that are the most detailed schlieren imagery of an aircraft in flight to date.

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