seareflectivity

Reflectivity of sea clutter

Syntax

nrcs = seareflectivity(scale,graz,freq)

nrcs = seareflectivity(scale,graz,freq,'Polarization',pol)

nrcs = seareflectivity(scale,graz,freq,'ScaleType',scaletype)

[nrcs,hgtsd,beta0,windvelocity] = seareflectivity(___)

Description

nrcs = seareflectivity(scale,graz,freq) returns the normalized radar cross section (nrcs) in meters squared for the specified sea scale scale, at the grazing angle graz, with the transmitted frequency freq.

nrcs = seareflectivity(scale,graz,freq,'Polarization',pol) specifies the polarization of the transmitted wave.

nrcs = seareflectivity(scale,graz,freq,'ScaleType',scaletype) specifies the scale type.

[nrcs,hgtsd,beta0,windvelocity] = seareflectivity(___) returns additional outputs:

• hgtsd — Standard deviation of the surface height for the specified sea state number as a scalar in meters

• beta0 — slope of the sea type in degrees. beta0 is 1.4 times the root mean square (RMS) surface slope. The surface σ⁰ value for sea clutter reflectivity is computed based on the NRL Sea Clutter Model by Gregers-Hansen and Mittal

• windvelocity — wind velocity in meters per second.

Examples

NRCS of Sea Clutter Patch

Calculate the NRCS of a sea clutter patch. Assume that the patch is the sea with sea state number equal to 2 and the radar system operates at a frequency of 30 GHz. Also assume the grazing angle is 10 degrees.

scale = 2;    
graz = 10;  
freq = 30e9;

Calculate the normalized NRCS for the sea clutter patch.

nrcs = seareflectivity(scale,graz,freq)

nrcs = 2.1555e-04

Use the normalized RCS to calculate the clutter patch RCS.

Input Arguments

scale — Sea state or wind scale

nonnegative integer

If you set scaletype to 'SeaState', scale is the sea state, specified as a nonnegative scalar between [0,8].

If you set scaletype to 'WindScale', scale is the wind scale, specified as a positive scalar between [1,9].

Example: seastate = 3

Dependency

Acceptable input values depend on the value of scaletype.

graz — Grazing angle

nonnegative scalar | N-length vector of grazing angles

Grazing angle, specified as a scalar or an N-length row vector of nonnegative grazing angles in degrees. Specifies the grazing angles of the clutter patch relative to the radar.

Example: graz_angle = 10

freq — Transmitted frequencies

10e9 (default) | scalar | positive M-length vector

Transmitted frequencies, specified as a scalar or positive M-length vector.

Example: freq = 7*10e9

pol — Polarization of transmitted wave

'H' (default) | 'V'

Polarization of transmitted wave, specified as 'H' for horizontal polarization or 'V' for vertical polarization.

Example: pol = 'V'

scaletype — Scale type

'SeaState' (default) | 'WindScale'

Scale type, specified as either:

• 'SeaState' — The function uses the Sea State model. When you specify this option, the scale input scale must be a nonnegative scalar between [0,8].

• 'WindScale' — The function uses the Beaufort Wind Scale model. When you specify this option, the scale input scale must be a positive scalars between [1,9].

Example: scaleType = 'WindScale'

Output Arguments

nrcs — Normalized radar cross section of surface reflectivity

N-length row vector | M-by-N matrix

Normalized radar cross section of the surface reflectivity, returned as either an N-length row vector or as an M-by-N matrix in linear units of meters squared. N is the length of the grazing angles graz and M is the length of the frequency vector freq.

hgtsd — Standard deviation of surface height

scalar

Standard deviation of the surface height, returned as a scalar in meters.

beta0 — Slope of the sea type

scalar

Slope of the sea type β₀, in degrees, returned as a scalar.

windvelocity — Wind velocity

scalar

Wind velocity, returned as a scalar in meters per second.

Algorithms

The sea reflectivity model is valid given the following conditions:

• Frequencies from 0.5 - 35 GHz

• Sea States from 0 - 6 (Wind Scale from 1 - 7)

• Grazing angles from 0.1 - 60 degrees

The model does not include variation with azimuth or wind direction. The NRL empirical model matches experimental results with an absolute deviation of about 2.2 to 2.3 dB for grazing angles from 0.1 to 10 degrees. A deviation of 2.6 dB can be seen for grazing angles above 10 degrees and below 60 degrees. The model for the height deviation, surface slope, and wind velocity is based on a model by Barton.

Extended Capabilities

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