A dual surface approach to near-field measurements of target strength

Abstract

Using near-field measurements of the pressure field over dual surfaces surrounding an immersed and insonified structure, an estimate of the structure’s target strength can be made. Choosing a cylindrical shaped surface, two measurement arrays enclosing the structure are formed with one array slightly larger than the other. At discrete points over the dual cylindrical shaped surfaces, two pressures are measured, and the pressure and the pressure gradient at these locations result. With the pressure and the pressure gradient, a discretized solution of the exterior Helmholtz integral is solved for the far-field pressure. Using the near-field measurements and this approach, far-field estimations of both radiation problems and target strength problems are possible. Using a rigid sphere as the insonified structure, the target strength problem is modeled and numerically solved using MATLAB. In this paper, an error analysis of this target strength application is presented. The effects on the estimated target strength due to different variables of the dual surface approach will be discussed, some of which include the following: open and closed dual surfaces; differences in the size of the dual surface; and variations on the density of the scanned dual surface. [Work supported by DARPA.]