seaSpectrum

Sea surface omnidirectional motion spectrum model

Since R2022a

Description

The seaSpectrum object creates a spectrum model for use in the SpectralModel property of the SeaSurface object.

Creation

Syntax

seaspect = seaSpectrum

seaspect = seaSpectrum(Name = Value)

Description

seaspect = seaSpectrum creates a seaSpectrum object seaspect with default property values. The default sea surface spectrum and spreading function are based on the Elfouhaily model. The Elfouhaily model is an omnidirectional and wind-dependent spectrum. The wave spectrum consists of the frequency spectrum and angular spreading function. The spreading function is symmetric about the wind direction and has both wave number and wind speed dependence.

seaspect = seaSpectrum(Name = Value) creates a seaSpectrum object with the specified property Name set to the specified Value. You can specify additional name-value pair arguments in any order as (Name1 = Value1, ..., NameN = ValueN).

Properties

SpectrumSource — Source of omnidirectional spectrum

'Auto' (default) | 'Custom'

Source of the omnidirectional wave spectrum, specified as 'Auto' or 'Custom'.

• Choosing 'Auto' creates an Elfouhaily sea spectrum. The object offers properties that tailor the Elfouhaily sea spectrum.

• Choosing 'Custom' allows you to specify the omnidirectional wave spectrum using the CustomSpectrum and WaveVectorSpacing properties.

Data Types: char | string

Resolution — Sea surface resolution

8 (default) | positive scalar | 1-by-2 vector of positive values

Sea surface resolution, specified as a positive scalar or as a 1-by-2 vector of positive values. The resolution vector takes the form [resolutionX resolutionY] where resolutionX and resolutionY denote the resolution in the x- and y- directions, respectively. If the resolution is a scalar, the x-resolution and y-resolution is the same.

The sea surface physical length is calculated as the difference of the limits of the Boundary property of the SeaSurface object in the x and y dimensions. The sea surface length has samples spaced by the Resolution property. The length should not be set below 0.02 m as the wave motion below 0.02 m is minimal. Units are in meters.

Data Types: double

CustomSpectrum — Omnidirectional wave spectrum

M-by-N matrix

Omnidirectional wave spectrum, specified as an M-by-N matrix. M and N dictate the inverse fast Fourier transfer (IFFT) length when returning the elevation data of the sea surface in the x and y dimensions, respectively.

The resolution for the custom case is calculated as Resolution = surface length./size(CustomSpectrum), where surface length is the sea surface physical length, calculated as the difference of the limits of the Boundary property of the seaSurface in the x and y dimensions.

Dependencies

To enable this property, set the value of the SpectrumSource property to 'Custom'.

Data Types: double

WaveVectorSpacing — Wave vector domain spacing

2*pi/1024 (default) | positive scalar | 1-by-2 real-valued vector

Positive wavevector domain spacing, specified as a scalar or a 1-by-2 dimension vector, [kx ky]. This property represents the wavevector spacing in the x and y dimensions, respectively. Units are radians/meter. This value is typically set as WaveVectorSpacing <= 2*pi/surface length where surface length is the sea surface physical length, calculated as the difference of the limits of the Boundary property on the seaSurface in the x and y dimensions.

Dependencies

To enable this property, set the SpectrumSource property to 'Custom'.

Data Types: double

Examples

Create Surface from Sea Spectrum

Create a 1024-by-1024 m square sea surface. Assume an NRL reflectivity model for a high sea state 6 with a wind speed of about 20 m/s and a fetch of 250 km. Set UseOcclusion in the SurfaceManager to false.

Create a radar scenario.

scene = radarScenario;

Model the reflectivity using the NRL model.

refl = surfaceReflectivitySea(Model = 'NRL',SeaState = 6, ...
    Polarization = 'V')

refl = 
  surfaceReflectivitySea with properties:

    EnablePolarization: 0
                 Model: 'NRL'
              SeaState: 6
          Polarization: 'V'
               Speckle: 'None'

rng(2033)
spec = seaSpectrum(Resolution = 2);
bnds = [0 1024; 0 1024];
srf = seaSurface(scene,Boundary = bnds, ...
    WindSpeed = 20,Fetch = 250e3, ...
    SpectralModel = spec);
mgr = scene.SurfaceManager;
mgr.UseOcclusion = false

mgr = 
  SurfaceManager with properties:

    EnableMultipath: 0
       UseOcclusion: 0
           Surfaces: [1x1 radar.scenario.SeaSurface]

x = linspace(srf.Boundary(1,1),srf.Boundary(1,2),1000);
y = linspace(srf.Boundary(2,1),srf.Boundary(2,2),1000);
[X,Y] = meshgrid(x,y);
X1 = X(:)';
Y1 = Y(:)';
hts = height(srf,[Y1;X1]);
hts = reshape(hts,length(x),length(y));
surf(x,y,hts)
axis equal
shading interp
ylabel('X (m)')
xlabel('Y (m)')
zlabel('Height (m)')

Sea Surface with Custom Wave Spectrum

Create a square sea surface with a custom wave spectrum. Import a JONSWAP wave spectrum with a moderate sea state. The spectrum is a 64-by-64 matrix with a physical length of 512 m.

scene = radarScenario(IsEarthCentered = false);

Add a sea surface to the scene with a custom spectrum

load('jonswap.mat');
spec = seaSpectrum(SpectrumSource = 'Custom', ...
    CustomSpectrum = Psi, WaveVectorSpacing = 2*pi/512)

spec = 
  seaSpectrum with properties:

       SpectrumSource: 'Custom'
       CustomSpectrum: [64x64 double]
    WaveVectorSpacing: 0.0123

srf = seaSurface(scene,Boundary = [-256 256; -256 256], ...
    SpectralModel = spec)

srf = 
  SeaSurface with properties:

                WindSpeed: 10
            WindDirection: 0
                    Fetch: Inf
            SpectralModel: [1x1 seaSpectrum]
        RadarReflectivity: [1x1 surfaceReflectivitySea]
    ReflectionCoefficient: [1x1 radar.scenario.SurfaceReflectionCoefficient]
          ReflectivityMap: 1
          ReferenceHeight: 0
                 Boundary: [2x2 double]

x = linspace(srf.Boundary(2,1),srf.Boundary(2,2),1000);
y = linspace(srf.Boundary(1,1),srf.Boundary(1,2),1000);
[X,Y] = meshgrid(x,y);
X1 = X(:)';
Y1 = Y(:)';
hts = height(srf,[Y1;X1]);
hts = reshape(hts,length(x),length(y));
surf(x,y,hts)
axis equal
shading interp
ylabel('X (m)')
xlabel('Y (m)')
zlabel('Height (m)')

References

[1] Elfouhaily, T., B. Chapron, K. Katsaros, and D. Vandemark. "A Unified Directional Spectrum for Long and Short Wind-Driven Waves." Journal of Geophysical Research: Oceans 102, no. C7 (July 15, 1997): 15781-96. https://doi.org/10.1029/97JC00467

[2] Tessendorf, Jerry. "Simulating Ocean Water." Presented at SigGraph, 1999 - 2004.

Version History

Introduced in R2022a