Using LiDAR to Identify Planar Measurement Regions in Ultrasonic Inspections of Complex Structures

Abstract

Acoustic Steady State Excitation Spatial Spectroscopy (ASSESS) is an ultrasonic inspection technique that was developed to rapidly evaluate large structures and identify regions of damage. An ultrasonic transducer affixed to the structure emits a single tone, and a scanning laser Doppler vibrometer (LDV) records the structures steady-state surface velocity response. Previous work has shown how local wavenumber can be estimated from the complex steady-state velocity response. This process has proved successful in detecting corrosion defects, delaminations, and regions of varying thickness. This work introduces a new processing method that utilizes a LiDAR generated point cloud representation of the scan region to identify and extract large planar sections from the measurement without causing distortion in the final wavenumber estimates. This new method uses the RANSAC algorithm to robustly extract planar sections and maps the complex steady-state response data onto a uniform grid on the detected planes. This is done in order to facilitate the use of an existing wavenumber estimation technique. We present wavefield and wavenumber results generated by applying this algorithm on a real-world dataset from a large area scan in an industrial structure with steel walls containing stringers, columns, and regions with different thicknesses.