Target strength pattern
tsSignature creates a sonar target strength (TS) signature object. You can
use this object to model an angle-dependent and frequency-dependent target strength pattern.
Target strength determines the intensity of reflected sound signal power from a target.
tssig = tsSignature
tsSignature object with default property values.
sets object properties using one or more
tssig = tsSignature(
Name,Value pair arguments.
Name is a property name and
Value is the
Name must appear inside single quotes
''). You can specify several name-value pair arguments in any order
Name1,Value1,...,NameN,ValueN. Any unspecified properties take
You can only set property values of
tsSignature when constructing the
object. The property values are not changeable after construction.
Pattern— Target strength pattern
[-30 -30; -30 -30](default) | Q-by-P real-valued matrix | Q-by-P-by-K real-valued array
Sampled target strength pattern, specified as a scalar, a Q-by-P real-valued matrix, or a Q-by-P-by-K real-valued array. The pattern is an array of TS values defined on a grid of elevation angles, azimuth angles, and frequencies. Azimuth and elevation are defined in the body frame of the target.
Q is the number of TS samples in elevation.
P is the number of TS samples in azimuth.
K is the number of TS samples in frequency.
Q, P, and K usually match
the length of the vectors defined in the
respectively, with these exceptions:
To model a TS pattern for an elevation cut (constant azimuth), you can specify
the TS pattern as a Q-by-1 vector or a
1-by-Q-by-K matrix. Then, the elevation
vector specified in the
Elevation property must have length
To model a TS pattern for an azimuth cut (constant elevation), you can specify
the TS pattern as a 1-by-P vector or a
1-by-P-by-K matrix. Then, the azimuth
vector specified in the
Azimuth property must have length
To model a TS pattern for one frequency, you can specify the TS pattern as a
Q-by-P matrix. Then, the frequency vector
specified in the
Frequency property must have length
Azimuth— Azimuth angles
[-180 180](default) | length-P real-valued vector
Azimuth angles used to define the angular coordinates of each column of the matrix
or array specified by the
Pattern property. Specify the azimuth
angles as a length-P vector. P must be greater
than two. Angle units are in degrees.
Elevation— Elevation angles
[-90 90](default) | length-Q real-valued vector
Elevation angles used to define the coordinates of each row of the matrix or array
specified by the
Pattern property. Specify the elevation angles as
a length-Q vector. Q must be greater than two.
Angle units are in degrees.
Frequency— Pattern frequencies
[0 1e8](default) | K-element vector of positive scalars
Frequencies used to define the applicable target strength for each page of the
Pattern property, specified as a K-element
vector of positive scalars. K is the number of TS samples in
frequency. K must be no less than two. Frequency units are in
Target strength at specified angle and frequency
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
tsSignature object and plot an elevation cut at 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
 Urich, Robert J. Principles of Underwater Sound, 3rd ed. New York: McGraw-Hill, Inc. 2005.