An Automated Photogrammetric Approach to the Estimation of Near-Surface Tornadic Wind Speeds

How can we estimate the velocity of near-surface winds in tornadoes? Early estimations of wind speeds in tornadoes were derived through photogrammetric observations of tornadoes from still imagery. More recently mobile Doppler radars have been helpful in the past to obtain tornadic wind speeds, however these observations have proven challenging to obtain near the ground. Direct measurements where the wind speeds matter the most, below 30 meters above ground level (AGL), are isolated at best and originate from in-situ probes. A new methodology will be outlined to characterize tornadic wind speeds using Particle Image Velocimetry (PIV) on multiple-perspective 2D observations of tornadoes near to the surface from controlled observers. Leveraging the high resolution of 4K video at 30 FPS, image differencing is used to determine wind speeds, and the high frame rate used to perform a statistical analysis to estimate uncertainty in the wind speeds. An advantage of this approach is that it allows estimate of the tangential wind speeds and vertical motion below 30 meters AGL within tornadic cases, and can be derived from widely available storm chaser video. To illustrate the potential of this method, this poster will focus on an analysis of a close range intercept from the 28 May 2019 tornado in Beloit, Kansas.