Examining the Relationship Between Debris Characteristics and Polarimetric Signatures using High-Resolution Mobile Radar Data, Photogrammetry, and Electromagnetic Scattering Simulations

Tornadic debris signatures (TDSs) provide information about the spatial distribution of tornado debris and have important operational applications for tornado detection and damage severity estimation. A key challenge to understanding TDSs is that the sizes, concentrations, and types of tornado debris are rarely known, so it is difficult to relate debris characteristics to polarimetric radar measurements. For example, qualitative debris characteristics can be inferred based damage surveys or land cover assessments, but little quantitative information is available. Another approach is to use numerical simulations to emulate TDSs. Such simulations allow the types, sizes, and concentrations of debris to be specified, but these debris characteristics do not necessarily translate directly to observed cases. The goal of this study is to perform a comparative analysis among an observational TDS, photogrammetric retrievals of debris characteristics, and corresponding numerically simulated TDSs. The intercomparisons will facilitate a better understanding of how debris characteristics are related to polarimetric radar variables and assess the strengths and weaknesses of numerical simulation approaches to modeling TDSs.

This study uses observations of an anticyclonic tornado and its TDS obtained with the Rapid X-band Polarimetric (RaXPol) radar on 24 May 2021. The anticyclonic tornado passed directly over the RaXPol and a photograph of the lofted tornado debris was taken as the tornado passed over the radar. Photogrammetric analyses are used to estimate debris sizes, concentrations, and orientations. From these estimates of debris characteristics, electromagnetic scattering calculations of vegetation are performed and used to simulate the TDS. The findings demonstrate that the combined photogrammetric and simulation-based studies can provide reasonably accurate retrievals of the observed radar variables. The strengths and limitations of the photogrammetric validation approach and electromagnetic scattering calculations will be discussed.