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surfaceReflectivity

Normalized reflectivity of surface

Description

The surfaceReflectivity System object™ creates a common interface for the surfaceReflectivityLand, surfaceReflectivityCustom, and surfaceReflectivitySea System objects.

To compute the normalized reflectivity:

  1. Create the surfaceReflectivity object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

Creation

Description

example

refl = surfaceReflectivity creates a normalized reflectivity object, refl, for a land surface. Use this object to generate a normalized radar cross section (NRCS) (also called surface σ0) as a function of frequency and grazing angle. This syntax creates a constant gamma land reflectivity model with a constant gamma value of -20 dB, which is representative of flatland.

refl = surfaceReflectivity(surfacetype) creates a normalized reflectivity object, refl, for a surfacetype specified as one of 'Land', 'Sea', or 'Custom'. Use this object to generate a normalized radar cross section (NRCS) (also called surface σ0) as a function of frequency and grazing angle.

example

refl = surfaceReflectivity(surfacetype,Name=Value) also creates a normalized reflectivity object for surface type surfacetype 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).

Example: refl = surfaceReflectivity('Land',Model="GIT",LandType="Soil",SurfaceHeightStandardDeviation=1) creates a normalized reflectivity object for land using the GIT model with a LandType of Soil and a SurfaceHeightStandardDeviation of 1.

Usage

Description

nrcs = refl(graz,freq) returns the normalized radar cross section nrcs at grazing angle graz and frequency freq.

[nrcs,speck] = refl(___) also returns multiplicative speckle speck.

Input Arguments

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Grazing or depression angle of a surface relative to the radar, specified as a scalar or an M-length row vector of real values. When the land Model property is set to 'Billingsley', the angle is interpreted as a depression angle depressionang between –90° and 90°. For all other models, the angle is interpreted as a grazing angle grazingang ranging from 0° to 90° . Units are in degrees.

Transmitted frequencies, specified as a positive scalar or N-length vector of positive values. Units are in Hz.

Example: freq = 7*10e9

Output Arguments

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Normalized surface reflectivity, returned as either a real-valued N-length row vector or a real-valued M-by-N matrix. Normalized reflectivity is also called normalized radar cross section. M is the length of the grazing angle or depression angle vector graz and N is the length of the frequency vector freq. nrcs is dimensionless but often expressed as m²/m².

Multiplicative speckle, returned as an N-length real-valued vector where N is the length of the frequency vector in freq.

Data Types: double

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

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Obtain the constant gamma normalized reflectivity for using the default gamma value of -20 dB at a frequency of 10 GHz and a grazing angle of 10 degrees.

grazAng = 10;
freq = 10e9;
refl = surfaceReflectivity
refl = 
  surfaceReflectivityLand with properties:

      Model: 'ConstantGamma'
      Gamma: -20
    Speckle: 'None'

nrcs = refl(grazAng,freq)
nrcs = 0.0017

Create a normalized reflectivity cross-section object for a land surface using the GIT model and a soil land type. Obtain the NRCS at a frequency of 10 GHz over grazing angles from 20 to 60 degrees. Assume a standard deviation of surface height of 1 m.

grazAng = 20:60;
freq    = 10e9;
refl = surfaceReflectivity('Land','Model','GIT','LandType','Soil', ...
    'SurfaceHeightStandardDeviation',1);
nrcs = refl(grazAng,freq);

Plot normalized reflectivities for grazing angles from 20 to 60 degrees.

plot(grazAng,pow2db(nrcs))
grid on
xlabel('Grazing Angle (deg)')
ylabel('NRCS (dB m^2/m^2)')
title('GIT Model')

Figure contains an axes object. The axes object with title GIT Model contains an object of type line.

Create a sea normalized reflectivity object using the default NRL model and a sea state of 2. Obtain the normalized reflectivity at 10 GHz over grazing angles from 0.1 to 10 degrees. Assume horizontal polarization.

grazAng = 0.1:0.1:10;
freq = 10e9;
ss = 2;
pol = 'H';

Use the surfaceReflectivity object to obtain the normalized reflectivity.

refl = surfaceReflectivity('Sea',SeaState = ss,Polarization = pol);
nrcs = refl(grazAng,freq);

Plot the reflectivity as a function of grazing angle.

plot(grazAng,pow2db(nrcs))
grid on
xlabel('Grazing Angle (deg)')
ylabel('NRCS (dB m^2/m^2)')
title('NRL Model, Horizontal Polarization')

Figure contains an axes object. The axes object with title NRL Model, Horizontal Polarization contains an object of type line.

Define a custom NRCS table using Nathanson reflectivity values for farmlands. Assume Rayleigh speckle. Next, calculate the RCS of a clutter patch and estimate the clutter-to-noise ratio at the receiver. Assume that the patch is 1000 meters away from the radar system. The azimuth and elevation beamwidths are 1 degree and 3 degrees, respectively. The grazing angle is 10 degrees. The pulse width is 10 microseconds. The radar operates at an L-band frequency of 1.5 GHz with a peak power of 5 kw. Use the general surfaceReflectivity object.

rng    = 1000;
bwAz   = 1;
bwEl   = 3;
graz   = 10;
tau    = 10e-6;
freq   = 1.5e9;
ppow   = 5000;

Configure a custom surface.

nathansonNRCS = db2pow([-35 -33 -32; -31 -30 -29; -29 -27 -25; ...
    -19 -17 -15; -14 -15 -14]);
nathansonFreq    = [1.5 3 6]*1e9;
nathansonGrazAng = [1.5 3 10 30 60];
refl = surfaceReflectivity('Custom',Reflectivity = nathansonNRCS, ...
    Frequency = nathansonFreq,GrazingAngle = nathansonGrazAng, ...
    Speckle = "Rayleigh")
refl = 
  surfaceReflectivityCustom with properties:

    Reflectivity: [5x3 double]
       Frequency: [1.5000e+09 3.0000e+09 6.0000e+09]
    GrazingAngle: [1.5000 3 10 30 60]
         Speckle: 'Rayleigh'
    SpeckleScale: 1.1284

[nrcs,n] = refl(graz,freq)
nrcs = 0.0013
n = 0.5108

Calculate the clutter RCS and apply multiplicative speckle

sigma = clutterSurfaceRCS(nrcs,rng,bwAz,bwEl,graz,tau)
sigma = 6.6253
rcs = sigma.*n   
rcs = 3.3841

Calculate clutter-to-noise ratio.

lambda = freq2wavelen(freq);
cnr = radareqsnr(lambda,rng,ppow,tau,'rcs',rcs)
cnr = 69.2976

Extended Capabilities

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

Version History

Introduced in R2022a