value

Target strength at specified angle and frequency

Syntax

tsval = value(tssig,az,el,freq)

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.

Input Arguments

tssig — Target strength signature

tsSignature object

Target strength signature, specified as a tsSignature object.

az — Azimuth angle

scalar | length-M real-valued vector

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

el — Elevation angle

scalar | length-M real-valued vector

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

freq — TS frequency

positive scalar | length-M vector with positive, real elements

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

tssval — Target strength

scalar | real-valued length-M vector

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

Object Functions

perturbations	Perturbation defined on object
perturb	Apply perturbations to object

Examples

Target Strength of Rigid Cylinder

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

Create a tsSignature object and plot an elevation cut at $$30^{\circ }$$ 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)')

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