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value

Target strength at specified angle and frequency

Description

tsval = value(tssig,az,el,freq) returns the value, tsval, of the target strength specified by the target strength signature object, tssig, computed at azimuth az, elevation el, and frequency freq. If the specified azimuth and elevation is outside of the region in which the target strength signature is defined, the target strength value, tsval, is returned as -Inf in dBsm.

example

Input Arguments

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Target strength signature, specified as a tsSignature object.

Azimuth angle, specified as scalar or length-M real-valued vector. Units are in degrees. The az, el, and freq arguments must have the same size. You can, however, specify one or two arguments as scalars, in which case the arguments are expanded to length-M.

Data Types: double

Elevation angle, specified as scalar or length-M real-valued vector. The az, el, and freq arguments must have the same size. You can, however, specify one or two arguments as scalars, in which case the arguments are expanded to length-M. Units are in degrees.

Data Types: double

TS frequency, specified as a positive scalar or length-M vector with positive, real elements. The az, el, and freq arguments must have the same size. You can, however, specify one or two arguments as scalars, in which case the arguments are expanded to length-M. Units are in Hertz.

Example: 20e3

Data Types: double

Output Arguments

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Target strength, returned as a scalar or real-valued length-M vector. Units are in dBsm.

Object Functions

perturbationsPerturbation defined on object
perturbApply perturbations to object

Examples

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Specify the target strength (TS) of a 5m long rigid cylinder immersed in water and plot TS values along an azimuth cut. Assume the short-wavelength approximation. The cylinder radius is 2m. The speed of sound is 1520 m/s.

L = 5;
a = 2;

Create an array of target strengths at two wavelengths. First, specify the range of azimuth and elevation angles over which TS is defined. Then, use an analytical model to compute the target strength. Create an image of the TS.

lambda = [0.12, .1];
c = 1520.0;
az = [-20:0.1:20];
el = [-10:0.1:10];
ts1 = ts_cylinder(L,a,az,el,lambda(1));
ts2 = ts_cylinder(L,a,az,el,lambda(2));
tsdb1 = 10*log10(ts1);
tsdb2 = 10*log10(ts2);
imagesc(az,el,tsdb1)
title('Target Strength')
xlabel('Azimuth (deg)')
ylabel('Elevation (deg)')
colorbar

Figure contains an axes object. The axes object with title Target Strength, xlabel Azimuth (deg), ylabel Elevation (deg) contains an object of type image.

Create a tsSignature object and plot an elevation cut at 30 azimuth.

tsdb(:,:,1) = tsdb1;
tsdb(:,:,2) = tsdb2;
freq = c./lambda;
tssig = tsSignature('Pattern',tsdb,'Azimuth',az,'Elevation',el,'Frequency',freq);
ts = value(tssig,30,el,freq(1));
plot(el,tsdb1)
grid
title('Elevation Profile of Target Strength')
xlabel('Elevation (deg)')
ylabel('TS (dBsm)')

Figure contains an axes object. The axes object with title Elevation Profile of Target Strength, xlabel Elevation (deg), ylabel TS (dBsm) contains 401 objects of type line.

function ts = ts_cylinder(L,a,az,el,lambda)
k = 2*pi/lambda;
beta = k*L*sind(el')*ones(size(az));
gamma = cosd(el')*ones(size(az));
ts = a*L^2*(sinc(beta).^2).*gamma.^2/2/lambda;
ts = max(ts,10^(-5));
end

function s = sinc(theta)
s = ones(size(theta));
idx = (abs(theta) <= 1e-2);
s(idx) = 1 - 1/6*(theta(idx)).^2;
s(~idx) = sin(theta(~idx))./theta(~idx);
end

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2018b