UACE2017 Proceedings: Experimental Validation of Circular Near-Field to Far-Field Transformation in Acoustic Tank Experiment

Session:
Target Echo Strength-Measurements and Modelling
Paper:
Experimental Validation of Circular Near-Field to Far-Field Transformation in Acoustic Tank Experiment
Author(s):
Anatoli Tsinovoy, Adva Bar-Am, Matan Kahanov
Abstract:
The mono-static target echo strength of a system of two Tungsten-Carbide spheres is measured as a function of azimuth aspect angle. To obtain an estimate of the far-field scattering we apply the Circular Near-Field to Far-Field Transformation (CNFFFT) on near-field measurements. A direct measurement of the far-field scattering was also performed, and used to validate the CNFFFT estimate. At first only partial agreement was achieved. The discrepancy was found to be due to the echoes from the apparatus used to hold and rotate the two spheres. A Fourier-imaging technique allowed us to filter out the unwanted echoes from both the direct and the transformed measurements. The imaging was implemented purely in the r-f domain, thus avoiding the Cartesian interpolation artefacts common to such processing. Excellent agreement between the two measurements was achieved following removal of the unwanted echoes. A comparison with the theory of scattering from two interacting hard spheres was made and adequate agreement was observed.
Download the full paper