885095927

ihc resonances of targcts as cylinders, water-filled or air-filled cylindri-cal shells, cavities, ctc. The rcsuits obtained by this new short pulsed method of idcntification agree with all those already published.

10:45

6PAa!0. Intelligent ultrasonic signal processing for solving inverse scattering problems. Wolfgang Sachse (Dept. of Theoret. and Appl. Mech., Comdl Univ._t Ithaca, NY 14853) and Igor Grabec (Univ. v Ljubljani, Ljubljani, Yugoslavia)

This paper describes new intelligent or neural-like proccssing pro-cedures by which thc ultrasonic signals scattcred by an obstacle can be processed to recover the characteristics of the unknown .scatterer. In particular, it focuses on the recently devcloped automutic modeler by which thc characteristics of the scattering phenomenon from a number of scatterers is leamed using a set of systematic learning data. It is demonstrated that ultrasonic signals measured in subsequent tests from an unknown scatterer can be processed to optimally recover the characteristics of the unknown obstacle. The solution of the invcrsc scattering problem that is obtained is thus completely empirical and not based on any elastodynamic theory. (Work supported by the National Science Foundation under Grant MSM-8904384.]

11:15

6PAal2. Optimization of the distance between transducer and scatterer in hydroacoustical modeling. Vladimir Genis (Biomed. Eng. and Sci. Inst., Drexcl Univ., 32nd and Chcstnut St., Philadelphia, PA 19104), I. Oboznenko (Kiev Polytech. Univ.), J. M. Reid, R. Raghavan, K. Soetanto, H. Oung, and X. M. Lu (Drcxcl Univ., Philadelphia, PA 19104)

This work was molivated by thc need to understand the cffect of phase and amplitudę variations on the scatterer's surfacc as well as the refiecting boundarics of the hydroacoustical tank on thc structure of the acoustical field in modeling. li is known that thc nuli positions of the spectral characteristics of the backscattered signals from various objects in water can yield information about their shape, diitiensions, orienta-tion, and structure. Accuracy of such measurements is aifected by the amplitudę and phasc variations on the scatterer surface and these vari-ations depend on thc minimum distance between the transmitter and scatterer positions. Calculations of these distances for acccptable dimen-sions of acoustical tanks were performed. Expressions were derivcd to correct thc minimum allowablc distance to prevent timc coincidencc of impulses from the scatterer and from the walls of the echoic acoustical tank.

11:00

6PAall. Characterization of white blood cells using inverse acoustic scattering. Xucai Chen, Robert E. Apfel (Dept. of Mech. Eng., Yale Univ., PO. Box 2159, New Havcn, CT 06520), and Stephen Wardlaw (School of Medicine, Yale Univ., New Haven, CT 06510)

I'he acoustic scattering functions of human leukocytes (white blood cells) in isotonic salinę solution are dctccted at two angles, along with information on their volumc obtained from electrozone sensing. The expcrimental apparatus has bcen reported earlier [J. Acoust. Soc. Am. Suppl. 1 84, SI63 (1988)]. Different procedures are used to invert the experimental data. Multidimensional histograms are generated and pat-tems in these histograms are used to recognize white celi subgroups. This technique may be developed into a diffcrential hematology ana-lyzer or combined with currently available analyzers to improve the measurement confidencc. (Work supported by the U.S. National Insti-tutes of Health through Grant 5R01CA39374.]

11:30

6PAal3. Making complex underwater scattering targets out of polystyrene foam. H. R. Suiter (Naval Coastal Syst. Ctr., Codę 2120, Panama City, FL 32407)

A method is described of casting polystyrene beads in smali quan-tities for laboratory use as scattering targcts. The method is easy and requires no specialized equipmcnt other than a mold. Two such targcts are described. One of them is a 4-period shallow wedge grating and the other a 7-period phasc grating constructed with acoustically hard alu-minum strips imbedded in the acoustically soft foam. Results of a tank experiment on these highly reflective targets will be given. The measured backscattered reflectivities are comparcd with simple Huygens-Fresnel-Kirchhoff diffraction theory in the high ku regime wherc the Kirchhoff approximation should work well. Agreement is satisfactory for the wedge gratings. For thc phase grating, the facet width must be used as a parameter to reproducc thc higher-order behavior. [Work supported by ONR.]

THURSDAY MORNING, 2 MAY 1991

PRATT A & B, 9:00 TO 11:30 A.M.

Session 6PAb

Physical Acoustics: Outdoor Sound Propagation

W. Pat Arnott, Chair

National Center for Physical Acoustics, Coliseum Driue, Uniuersity, Mississippi 38677

Contributed Papers

9:00

6PAbl. One-dimensional model of turbulence-induced distortion of sonie boom prohles. Andrew A. Piacsek (Grad. Próg. in Acoust., Penn State Univ., P. O. Box 30, State College, PA 16804)

In a recent paper (AIAA-90-4031), Pierce and Sparrow have sug-1951 J. Acoust. Soc. Am.. Vol. 89, No. 4. Pt. 2. April 1991

gested that the prediction of the distortion of sonie booms by atmo-spheric turbulence can be carried out using modification of thc Fried-lander senes theory that gives waveforms as a power senes in time relative to wavc onset. The present paper explores basie mathematical problems associated with that theory by analysis of a simplified mathematical model. A step pulsc in acoustic pressure propagating in the

121st Meeting: Acoustical Sociefy ol America 1951