Stereoscopic High-Speed Imaging For 3D Tracking Of Coughed Saliva Droplets In The Context Of COVID-19 Spreading

Abstract

Droplets generated by talking and coughing play a major role in the spreading of COVID-19. There is thus a need for accurate measurements of the physical properties of exhaled droplets, including their number, speed and direction. Several challenges are associated with imaging coughed droplets such as high droplet speed near the mouth where both short exposure time to freeze droplet motion and kHz recording rate to resolve their displacement is required. In addition, as a highly non-symmetrical spray system is formed from a cough, three-dimensional visualization is necessary to faithfully capture coughing events. In this work, a 3D, high-speed imaging technique is presented that facilitates such challenging measurements. A laser beam with a probe volume 15 mm thick - 120 mm high is formed and illuminates droplets exiting the mouth imaged using two high-speed cameras. Data has been recorded for four different male subjects where 3D droplet speed and direction has been extracted for 10 coughs each. The maximum speed for a single cough has been estimated to vary between 11 and 45 m/s and the average droplet speed has been found to be in the range 6.5 - 8.7 m/s. These results will be used as input parameters to improve simulation models of droplet transport in the context of virus spreading.