Radar Surface Clutter Simulation
Surface clutter consists of radar reflections that emanate from terrain, vegetation, man-made structures, and ocean waves. Incorporate surface clutter into your Radar Toolbox simulations to determine if monostatic narrowband radar systems can distinguish between clutter and targets of interest. Topics covered include:
Overview of Surface Clutter Capabilities
This table provides an overview of surface clutter modeling capabilities in Radar Toolbox organized by power-level, measurement-level, and waveform-level applications. The highest-fidelity simulations model dynamic scenarios with moving targets and support site-specific, geolocated terrain models and atmospheric refraction on a curved Earth.
| Fidelity | Usage | Radar Toolbox Functionality | Output | Computational Complexity | Dynamic Scenario | Site-Specific | Curved Earth |
|---|---|---|---|---|---|---|---|
| System-level analysis, range only | clutterSurfaceRCS | Clutter patch RCS as a function of range | Low | — | — | — | |
| System-level analysis, range and Doppler | clutterSurfaceRangeDopplerRCS | Clutter patch RCS as a function of range and Doppler | Low | — | — | — | |
| Interactive system-level analysis | Radar Designer app | Export plots, metrics, and MATLAB® scripts | Low | — | — | ✔ | |
Algorithm design Tracker design and tuning | radarDataGenerator in a radarScenario
with clutterGenerator enabled | Detections Track reports | Medium | ✔ | ✔ | ✔ | |
AI training Algorithm design | constantGammaClutter
and gpuConstantGammaClutter | I/Q signals of clutter | Medium | — | — | ✔ | |
End-to-end analysis in range and Doppler Algorithm design |
| I/Q signals of scenario, including targets in clutter | Medium | ✔ | — | — | |
High fidelity, end-to-end analysis Algorithm design | radarTransceiver in a radarScenario with
clutterGenerator enabled and
ScattererDistribution set to "Uniform" | I/Q signals of scenario, including targets in clutter | High | ✔ | ✔ | ✔ |
Power-Level Simulation
Power-level simulations of radar systems account for transmitted and received power and are used for system-level design. You can perform link budget analysis to predict performance metrics like detection range and signal-to-noise ratio using the Radar Designer app. Power-level applications that incorporate clutter are based on clutter patch Radar Cross Section (RCS) calculations and include:
Clutter-to-noise ratio (CNR) as a function of range
CNR as a function of range and Doppler
Target detectability studies
This tables provides information on power-level surface clutter models, capabilities, and simulation approaches available in Radar Toolbox, organized by application.
| Application | How to Model Using Radar Toolbox | Examples | Additional Information |
|---|---|---|---|
Calculate clutter patch Radar Cross Section (RCS) to determine:
|
Use the RCS of a clutter patch as an
input into | Return the Normalized Radar Cross Section (NRCS) for built-in surface models using:
| |
Analyze surface clutter presentation in range-Doppler space for:
|
Use the RCS of a clutter patch as an
input into | Return the Normalized Radar Cross Section (NRCS) for built-in surface models using: | |
Assess system performance of clutter-limited systems for:
| Radar Designer app performs interactive system-level analysis that includes the clutter-to-noise ratio as a function of range (CNR vs Range) plot. Radar Designer app supports:
| Use Radar Designer to:
|
Measurement-Level Simulation
Measurement-level simulations of radar systems account for signal processing chain
gains and losses, measurement uncertainty, and environmental effects to provide
probabilistic target detections. You can use the statistical radar model, radarDataGenerator, as part of a radar scenario to assess performance
metrics such as probability of detection in the presence of noise and false alarms.
Measurement-level applications that incorporate clutter include:
Target detectability studies
Tracker tuning
Clustering analysis
This tables provides information on measurement-level surface clutter models, capabilities, and simulation approaches available in Radar Toolbox.
| Application | How to Model Using Radar Toolbox | Examples | Additional Information |
|---|---|---|---|
Generate probabilistic detections of targets in clutter within a dynamic scenario that includes processing chain gains and losses for:
| Use
|
Surfaces are defined as
|
Waveform-Level Simulation
Waveform-level simulations account for the signal and data processing chain and
generate high-fidelity I/Q signals. You can use constantGammaClutter and gpuConstantGammaClutter to quickly model I/Q signals of surface clutter.
If you want to model targets in clutter, use radarTransceiver as part of a radar scenario with sensor and target
platforms. Waveform-level applications that incorporate clutter include:
Algorithm design and testing
End-to-end analysis of radar systems
This tables provides information on waveform-level surface clutter models, capabilities, and simulation approaches available in Radar Toolbox, organized by application.
| Application | How to Model Using Radar Toolbox | Examples | Additional Information |
|---|---|---|---|
Simulate large amounts of surface clutter as I/Q signals to:
| Use
| Return the gamma value for built-in terrain types using
Plot the angle-Doppler
response of the simulated clutter using | |
Simulate pulse-Doppler I/Q signals of targets in clutter within a dynamic scenario to:
| Use
|
Surfaces in this scenario are defined as
| |
Simulate high-fidelity I/Q signals of targets in clutter within a dynamic scenario to:
| Use
|
Surfaces in this scenario are defined as
|
Normalized Radar Cross Section (NRCS)
Normalized Radar Cross Section (NRCS) is a dimensionless quantity that provides a
measure of the reflectivity of a surface, per unit area. Use built-in surface models
available in landreflectivity, seareflectivity, and surfaceReflectivity to determine NRCS.
surfaceReflectivity system objects were specifically designed to
support radarScenario. Surface models are generally grazing angle
dependent. Clutter elements in the models have a Gaussian distribution, meaning that
discrete clutter elements, such as buildings or individual trees, are not
modeled.
landreflectivity and surfaceReflectivityLand contain several land models
(Barton, Billingsley,
APL, GIT, Morchin,
Nathanson, ConstantGamma, and
UlabyDobson). Although most land models are considered to be
polarization independent, theUlabyDobson model incorporates
polarization. Each land model supports multiple land types that are valid over
predefined grazing angles and frequencies (see Land Reflectivity Models and Land Types). landroughness returns properties of the Barton model, including height
standard deviation, slope, and vegetation type. The figure below shows NRCS as a
function of grazing angle for two land types.
seareflectivity and surfaceReflectivitySea contain several sea models
(NRL, APL, GIT,
Hybrid, Masuko,
Nathanson, RRE,
Sittrop, and TSC) that are polarization
dependent. Sea surface models are valid over predefined grazing angles and frequencies
(see Sea Reflectivity Models) and account for
the radar look angle, which is defined with respect to the wind direction (the look
angle is zero when the radar is pointed upwind). searoughness returns model height standard deviation, slope, and wind
velocity for a given sea state or wind scale.
Radar Cross Section (RCS)
Radar Cross Section (RCS) is a measure of the amount of energy returned from a
surface, in units of area. RCS is a function of the radar's frequency, grazing angle,
and range and depends on the surface NRCS. Surfaces with larger NRCS reflect more
strongly and thus return more powerful clutter echoes. Use clutterSurfaceRCS and clutterSurfaceRangeDopplerRCS to calculate surface RCS. Clutter patch
RCS is calculated internally during a radarScenario simulation.
clutterSurfaceRCS calculates clutter using a Beam-Illuminated Approximation or Pulse-Illuminated Approximation approximation.
Beam-limited clutter tends to occur at high grazing angles and pulse-limited clutter
tends to occur at low grazing angles. See Beam-Limited and Pulse-Limited Clutter. The Radar Designer
app uses the same calculations for RCS as clutterSurfaceRCS.
clutterSurfaceRangeDopplerRCS describes the distribution of
surface clutter over range and Doppler space and supports Doppler wrapping (see RCS with Doppler Wrapping). See Range-Doppler Cells in Cartesian Space and Range-Doppler Map (RDM) for more
information on the distribution of surface clutter in range-Doppler space relative to
Cartesian space. Clutter I/Q simulated with "RangeDopplerCells"
enabled in clutterGenerator as part of a radarScenario
are equivalent to those generated using the
clutterSurfaceRangeDopplerRCS RCS in a custom simulation
demonstrated in Predict Surface Clutter Power in Range-Doppler Space.
radarScenario determines clutter patch RCS within the scenario
simulation using information contained in landSurface,
seaSurface, and customSurface objects.
Land/sea/custom surfaces in the scenario are managed by surfaceManager
and contain surfaceReflectivity objects that support uncorrelated,
multiplicative speckle. The addition of speckle makes clutter appear noisier for imaging
applications.
clutterGenerator Scatterer Distribution and Regions
Attach clutterGenerator to a radarScenario to model surface
clutter radar returns in radarTransceiver and
radarDataGenerator simulations. Clutter returns emanate from
landSurface, seaSurface, and
customSurface objects in the scenario. Land/sea/custom surfaces are
managed by surfaceManager and contain
surfaceReflectivity objects. Introduction to Radar Scenario Clutter Simulation details how to generate monostatic
surface clutter signals and detections in a radar scenario.
clutterGenerator approximates reflections from large continuous
surfaces as a set of point scatterers. When the
ScattererDistribution property is set to the default value of
"Uniform", the Resolution property
determines the density of clutter patches using perturbed grid points (see Perturbed Grid Patching). When the
ScattererDistribution property of
clutterGenerator is set to "RangeDopplerCells"
(this selection is compatible with radarTransceiver but not
radarDataGenerator), a faster range-Doppler-adaptive approach is
used in which one clutter scatterer per range-Doppler resolution cell is modeled. The
NumRepetitions property or the
radarTransceiver, along with the radar's PRF, determines the
Doppler resolution of the adaptive scatterers.
You can designate specific clutter regions in clutterGenerator. Set
UseBeam to true to automatically generate
mainlobe clutter (see Mainlobe Clutter). You can also call
ringClutterRegion on the clutter generator object to specify
ring-shaped clutter regions within which clutter is generated (see Ring-Shaped Clutter Regions).
Perturbed Grid Patching
clutterGenerator approximates reflections from large continuous
surfaces as a set of point scatterers using perturbed grid patching. This method
involves perturbing a set of grid points pseudo-randomly and results in scatterers
that have a fairly uniform density that are sufficiently randomized to achieve a
robust Monte Carlo integration. The figure below shows original grid points in blue
and perturbed points in red.
The clutterGenerator
Resolution property determines the nominal spacing of clutter
patches. A smaller nominal resolution value results in more scatterers per unit
area. The nominal resolution value should be set to the smallest expected ground
resolution of the radar system over the clutter regions of interest to get at least
one scatterer per resolution cell. Ideally, you should model eight scatterers per
resolution cell. Decreasing the Resolution value results in
more scatters per resolution cell. The down-range resolution corresponds to the
radar's range resolution and is therefore a fixed value. The cross-range resolution
is determined by the radar's beamwidth and the distance to the target. Typically,
the down-range resolution is smaller (better) than the across-range resolution,
which depends on slant range.
Mainlobe Clutter
The UseBeam property enables the modeling of mainlobe
clutter, or unwanted reflections that originate from the antenna pattern, based on
the shape of the beam footprint. The beam footprint is the projection of a beam of a
given beamwidth onto a surface.
Most phased arrays supported by radarTransceiver and
clutterGenerator have a conical beamshape and an elliptical
normalized footprint that is assumed to have a 3 dB beamwidth in both azimuth and
elevation. phased.ULA has a fan-shaped beamshape
that is also supported and is assumed to have a 3 dB beamwidth in the plane
perpendicular to the array axis.
radarDataGenerator has a rectangular field of view, with azimuth
and elevation set by the FieldOfView property.
clutterGenerator supports this rectangular beamshape.
Ring-Shaped Clutter Regions
You can call ringClutterRegion on the clutter generator object to specify
custom-sized ring-shaped clutter regions within which clutter is generated. A ring
clutter region is defined by a minimum and maximum ground range and an extent and
center angle in azimuth. These regions are useful for capturing sidelobe and
backlobe clutter return, mainlobe clutter return outside the 3 dB beamwidth (for a
radarTransceiver phased array), or to generate clutter from any
other region of interest, such as at the location of a target platform. Because
radarDataGenerator is a statistics-based detectability
simulator and does not contain a complete antenna pattern, clutter modeling is
limited to the mainlobe only. To enable clutter simulation for
radarDataGenerator, set the UseBeam
property to true.
The figure below illustrates two ring clutter regions, one directly underneath the
radar for capturing altitude return, and another for capturing some backlobe clutter
return. The beam footprint region for the radarTransceiver phased
array is displayed as a magenta ellipse where the beam intersects the ground. See
Introduction to Radar Scenario Clutter Simulation for more information.
References
[1] Barton, David Knox. Radar Equations for Modern Radar. Artech House, Boston, 2013.
