Analysis of Flow Structures in the Barringer Meteor Crater using Thermal Infrared Data collected during the METCRAX II Field Experiment

The Second Meteor Crater Experiment (METCRAX II) was conducted at Barringer Meteor Crater in Arizona in October 2013 to examine downslope windstorm-type flows (DWFs) that occur when a mesoscale drainage flow forming outside the crater basin interacts with the crater topography.

In addition to the extensive meteorological setup, three thermal infrared (TIR) cameras (VarioCAMs, InfraTec, Dresden, Germany) pointed into the crater and recorded the surface temperatures during three intensive observational periods (IOPs) that were carried out on undisturbed and clear-sky nights. The TIR data were georeferenced using the field of view of the camera to construct virtual lines of sight for every pixel to find intersections with a high-resolution digital elevation model. Atmospheric correction has been applied using two different methods (MODTRAN5 and a method suggested by InfraTec). Surface emissivity was assumed to be 1 but the effect of an emissivity correction was estimated. The TIR temperatures showed positive correlations to a reference pyrgeometer measurement located on the crater floor although there were differences in the absolute measurement values of the three cameras. Furthermore time-sequential thermography (TST) was used to decompose the absolute temperature values into spatiotemporal fluctuations to visualize turbulence and flow structures on the crater's surface.

In this study the influence of DWFs on the surface temperature distribution of the crater was analyzed in detail. Flows coming down the southwest sidewall produced band-like structures with higher surface temperatures that penetrated a shallow but strong inversion on the crater floor. The warming sometimes advanced deeper onto the crater floor (IOP4) and sometimes was less distinct and only visible along the SW sidewall (IOP2). With the georeferenced dataset, profiles of crater surface temperatures could be examined to produce a phenomenology for the three IOP nights. The coupling between the air flow and the surface was investigated highlighting the smoothing effects of turbulence. The flow structures are visualized by short videos showing the spatiotemporal fluctuations of surface temperatures.