
Accession Number : ADA314530
Title : Efficient Calculation of Directivity Indices for Certain ThreeDimensional Arrays.
Descriptive Note : Final rept.,
Corporate Author : NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV RI
Personal Author(s) : Nuttall, Albert H. ; Cray, Benjamin A.
PDF Url : ADA314530
Report Date : 26 JUL 1996
Pagination or Media Count : 44
Abstract : Array directivity is defined as the ratio of the output signaltonoise ratio of an array to the input signaltonoise ratio at an omnidirectional element in an isotropic noise field. Calculation of directivity is obtained by integrating the magnitudesquared response of the array over all angles of incidence. In spherical coordinates, these arrival angles are denoted by an azimuthal angle, theat, and a polar angle, phi. Hence, calculation of the directivity requires a twofold integration over the angular space defined by the azimuthal and polar angles. Except for a few simple array geometries and unique frequencies, analytical solutions for this twofold integration can generally not be obtained. Numerical integration techniques must therefore be used to calculate directivity. For largeaperture arrays, consisting of thousands of array elements, conventional integration procedures, such as a double application of Simpson's rule over azimuth and elevation angles, is woefully time consuming and can be potentially inaccurate. This study presents a number of procedures which dramatically decrease the time required to numerically calculate directivity for certain array shapes and weights. Algorithms, written on a SUN SPARC station 10 in Fortran 77, are provided in the appendices. However, the factorization procedures described here can be implemented equally well in other programming languages, such as MATLAB. TM The enclosed programs, which incorporate all of the procedures described herein, can be used to calculate the directivity of certain planar arrays, as well as threedimensional arrays which are conformal to the cylindrical portion of a submarine hull, for example.
Descriptors : *SIGNAL TO NOISE RATIO, *SONAR ARRAYS, COMPUTER PROGRAM DOCUMENTATION, ALGORITHMS, SIGNAL PROCESSING, OPTIMIZATION, ACOUSTIC WAVES, ANGLE OF ARRIVAL, DIRECTION FINDING, THREE DIMENSIONAL, FORTRAN, NUMERICAL INTEGRATION, NOISE REDUCTION, ANGLE OF INCIDENCE, AZIMUTH, SUBMARINE HULLS, PLANE WAVES, SONAR SIGNALS, ACOUSTIC FIELDS, OMNIDIRECTIONAL.
Subject Categories : Acoustic Detection and Detectors
Distribution Statement : APPROVED FOR PUBLIC RELEASE