Micrometric deformation imaging at W-Band

Abstract

The measurement of scattered signals at W Band can be exploited to form images of small deformations with precisions in the order of tenths of micrometers. In this paper an Interferometric Synthetic Aperture Radar setup is proposed to form high resolution reflectivity images and deformation maps of dielectric or metallic surfaces. First, the system geometry of observation based on a linear motion of the radar antennas is described. A CW frequency domain measurement provides the wide band required for high resolution imaging. The scattered field data is focused on the surface spatial domain using a combination of range compression based on Inverse Fourier Transform combined with a backprojection algorithm to form the synthetic aperture with a high cross range resolution. The focusing performance has been assessed by numerical simulations and experimental measurements of simple scattering objects like spheres and trihedrals. Interferometric images of controlled displacements have been obtained showing a good agreement between real and measured displacements. A representative surface deformation test has been also carried out using a metallic rough surface. The interferometric phase difference between acquisitions can be used to image local deformations in the order of tens of micrometers from a range of several meters. Likewise the interferogram coherence shows the degree of decorrelation of the radar reflectivity which provides valuable information for surface random change assessment.