### ASA 125th Meeting Ottawa 1993 May

## 5aSA12. A dual surface approach to near-field measurements of target
strength.

**Michael A. Sartori
**

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Joseph A. Clark
**

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*Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000
*

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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.]