Radar 2009 A_10 Radar Clutter1

52
IEEE New Hampshire Section Radar Systems Course 1 Clutter 11/1/2009 IEEE AES Society Radar Systems Engineering Lecture 10 Part 1 Radar Clutter Dr. Robert M. O’Donnell IEEE New Hampshire Section Guest Lecturer

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Transcript of Radar 2009 A_10 Radar Clutter1

Page 1: Radar 2009 A_10 Radar Clutter1

IEEE New Hampshire SectionRadar Systems Course 1Clutter 11/1/2009 IEEE AES Society

Radar Systems Engineering Lecture 10 Part 1

Radar Clutter

Dr. Robert M. O’DonnellIEEE New Hampshire Section

Guest Lecturer

Page 2: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 2Clutter 11/1/2009

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Block Diagram of Radar SystemTransmitter

WaveformGeneration

PowerAmplifier

T / RSwitch

Antenna

PropagationMedium

Target RadarCross Section

Photo ImageCourtesy of US Air ForceUsed with permission.

PulseCompressionReceiver Clutter Rejection

(Doppler Filtering)A / D

Converter

General Purpose Computer

Tracking

DataRecording

ParameterEstimation Detection

Signal Processor Computer

Thresholding

User Displays and Radar Control

Buildings(Radar Clutter)

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Outline

Motivation

Backscatter from unwanted objects

Ground

Sea

Rain

Birds and Insects

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Why Study Radar Clutter?

BirdFlock

Ground Urban Buildings

Chaff

Targets

Target

Rain

GroundHills

Sea

Courtesy MIT Lincoln LaboratoryUsed with permission

Naval Air Defense Scenario

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Radars for Which Clutter is a Issue

SPS-48

OTH Radar

AEGIS SPY 1

AWACS E-3A

SPS-49

HAWKEYE E-2C

Courtesy of US Navy

Courtesy of US NavyCourtesy of US Air Force

Courtesy of ITT GillfillanUsed with permission

Courtesy of US Navy

Courtesy of RaytheonUsed with permission

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Radars for Which Clutter is a Issue

F-16 APG-68

FAA ARSR-4 TPS-79

JOINT STARS E-8 AEROSTAT RADAR APG-63 V(2)

Courtesy of Alphapapa

Courtesy of Northrop GrummanUsed with permission

Courtesy of US Air Force

Courtesy of BoeingUsed with permission

WEDGETAIL

Courtesy of Wings777Courtesy of Lockheed MartinUsed with permission

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How to Handle Noise and Clutter

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How to Handle Noise and Clutter

If he doesn’t take his arm off

my shoulder I’m going to hide

his stash ofHershey Bars !! Why does Steve

always talk me into doing ridiculous

stunts like this ?

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Typical Air Surveillance Radar (Used for Sample Calculations)

Frequency

S-band

(2700–2900 MHz)

Instrumented range

60 nautical miles

Peak power

1.4 mw

Average power

875 W

Pulse repetition

(700–1200 Hz)

frequency

1040 Hz average

Antenna rotation rate

12.8 rpm

Antenna size

4.8 m ×

2.7 m

Antenna gain

33 dB

Radar Parameters

FAA -

Airport Surveillance Radar

Courtesy of MIT Lincoln LaboratoryUsed with permission

Page 10: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 10Clutter 11/1/2009

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Outline

Motivation

Backscatter from unwanted objects

Ground

Sea

Rain

Birds and Insects

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Outline -

Ground Clutter

Introduction

Mean backscatter–

Frequency–

Terrain type–

Polarization

Temporal statistics

Doppler spectra

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Attributes of Ground Clutter

Mean value of backscatter from ground clutter–

Very large size relative to aircraft–

Varies statistically Frequency, spatial resolution, geometry, terrain type

Doppler characteristics of ground clutter return–

Innate Doppler spread small (few knots) Mechanical scanning antennas add spread to clutter

Relative motion of radar platform affects Doppler of ground clutter

Ship Aircraft

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Ground Based Radar Displays

0 dB

Mountainous Region ofLakehead, Ontario, Canada

PPI Set for 30 nmi.

Shrader, W. from Tutorial on MTI Radar presented at Selenia, Rome, Italy.Used with permission.

Plan Position Indicator (PPI) Display

Map-like DisplayRadial distance to center RangeAngle of radius vector AzimuthThreshold crossings

Detections

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Photographs of Ground Based Radar’s PPI (Different Levels of Attenuation)

Attenuation Level 0 dB Attenuation Level 60 dB

Mountainous Region ofLakehead, Ontario, Canada

PPI Set for 30 nmi.

Shrader, W. from Tutorial on MTI Radar presented at Selenia, Rome, Italy.Used with permission.

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Photographs of Ground Based Radar’s PPI

0 dB

0 dB

10 dB

20 dB 30 dB

40 dB 50 dB

60 dB 70 dBShrader, W. from Tutorial on MTI Radar presented at Selenia, Rome, Italy.Used with permission.

Different Levels of Attenuation

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Geometry of Radar Clutter

Elevation View

Radar

h

φ

cT / 2

½

cT sec φ

Plan View

RadarClutter

BRθ

0 Aσ

σ =

A = RθB

cT sec φ]Courtesy of MIT Lincoln LaboratoryUsed with permission

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Calculation of Ground Clutter

• σ Clutter

= σo

AA = σoc T2

R θB

• Typical Value of σo

= -20 dB =

0.01 m2

m2

– For ASR-9 (Airport Surveillance Radar)

R = 60 kmc T2

= 100m θB = 1.5o

= 0.026 radians

• σ Clutter

= x 100 m x 60,000 m x 0.026 radians = 1500 m2

∴ Must suppress clutter by a factor of1500 x 20 = 30,000 = 45 dB

0.01 m2

m2

For σ Target

= 1 m2

For gooddetection

σ Clutter

σ Target =1

1500 σ Clutter

σ Target = 20

Small single-engine

aircraft

INPUT OUTPUT

Courtesy of MIT Lincoln LaboratoryUsed with permission

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Joint U.S./Canada Measurement Program

Phase One radar–

VHF, UHF, L-, S-, X-bands

Measurements conducted 1982 –

1984

Archival data at Lincoln Laboratory

42 sites

Data shared with Canada

and the United Kingdom

Courtesy of MIT Lincoln LaboratoryUsed with permission

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Joint U.S./Canada Measurement Program

Radar System ParametersPhase One Radar

Frequency Band MHz) Antenna Gain (dB) Antenna Beamwidth Az (deg) El (deg) Peak Power (kW) Polarization PRF (Hz) Pulse Width (µs) Waveform A/D Converter Number of Bits Sampling Rate (MHz)

VHF

13

13 42

10

HH,VV

500

0.1, 0.25, and 1

Uncoded

CW Pulse

13

10, 5, 1

UHF

25

5 15

10

HH,VV

500

0.1, 0.25, and 1

Uncoded

CW Pulse

13

10, 5, 1

L-Band

28.5

3 10

10

HH,VV

500

0.1, 0.25, and 1

Uncoded

CW Pulse

13

10, 5, 1

S-Band

35.5

1 4

10

HH,VV

500

0.1, 0.25, and 1

Uncoded

CW Pulse

13

10, 5, 1

X-Band

38.5

1 4

10

HH,VV

500

0.1, 0.25, and 1

Uncoded

CW Pulse

13

10, 5, 1

Courtesy of MIT Lincoln LaboratoryAdapted from Billingsley, Reference 2

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Clutter Physics

Depression

Angle

Microshadowing

Visible

Terrain

Clutter Coefficient σ o

RH

Courtesy of MIT Lincoln LaboratoryUsed with permission

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dB11F4o −=σ

Histograms of Measured Clutter Strength σoF4

(dB)

-80 -70 -60 -50 -40 -30 -20 -10σ°F4 (dB)

dB55F4o −=σ

FarmlandVHF

-80 -70 -60 -50 -40 -30 -20 -10σ°F4 (dB)

0

5

10

Perc

ent

FarmlandX Band

dB23F4o −=σ

10ForestX Band

dB24F4o −=σ

-70 -60 -50 -40 -30 -20 -10 0σ°F4 (dB)

0

50 90 99

5

Perc

ent

0

0

5

5

10

10Forest

VHF

σ°F4 (dB)

5050 90 999099

50 90 99

-70 -60 -50 -40 -30 -20 -10 0

BlueLine

IsMean

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Clutter Physics

Depression

Angle

Microshadowing

Visible

Terrain

Clutter Coefficient σ o

RH

Clutter

Histogram

Weibull

Parameters

wa (A)

w (f)σ o

4F (dB)σ o

Courtesy of MIT Lincoln LaboratoryUsed with permission

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Weibull Probability Density Function

The Weibull and Log Normal distributions are used to model ground clutter, because they are too parameter distributions which will allow for skewness (long tails) in the distribution of ground clutter

For , the Weibull distribution degenerates to an Exponential distribution in power (a Rayleigh distribution in voltage)

1aw =

( ) ( ) b50

b2

xxlog

b50

1b2 e

xx2logbxp

−−

⋅⋅⋅

=

4o

w

w

50

Fx

aa/1b

xx

σ=

=

=

= Median value of

In units of m2/m2

Weibull shape parameter

Page 24: Radar 2009 A_10 Radar Clutter1

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Clutter Physics

Depression

Angle

Microshadowing

Visible

Terrain

Clutter Coefficient σ o

RH

Clutter

Histogram

Weibull

Parameters

wa (A)

w (f)σ o

4F (dB)σ o

Lobing

Free Space

Multipath

Propagation Factor F4Clutter Strength = Fσ o

Courtesy of MIT Lincoln LaboratoryUsed with permission

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Clutter Physics

Depression

Angle

Microshadowing

Visible

Terrain

Clutter Coefficient σ o

RH

Clutter

Histogram

Weibull

Parameters

wa (A)

w (f)σ o

4F (dB)σ o

1)

Radar Parameters•

Frequency, f•

Spatial resolution, A

2)

Geometry•

Depression angle

(Range R, Height H)

3)

Terrain Type•

Landform•

Land cover

Lobing

Free Space

Multipath

Propagation Factor F4Clutter Strength = Fσ o

Courtesy of MIT Lincoln Laboratory Used with permission

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Mean Ground Clutter Strength vs. Frequency

Mea

n of

σ°F

4(d

B)

VHF UHF L- S- X-band

10,0

00

100

1,00

0

Frequency (MHz)

General Rural (36 Sites)

Range

Resolution

(m)

Key

Polarization

H150V150H15/36V15/36

0

–10

–20

–30

–40

–50

–60

–70

–80

Courtesy of MIT Lincoln LaboratoryUsed with permission

Page 27: Radar 2009 A_10 Radar Clutter1

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Major Clutter Variables in Data Collection

Terrain type–

Forest–

Urban–

Farmland–

Mountains–

Farmland–

Desert, marsh, or grassland (few discrete scatterers)

Terrain slope:–

High

(>2°)–

Low

(<2°) Moderately low

(1°

to 2°) Very low

(<1°)

Depression angle–

High

to 2°–

Intermediate

0.3°

to 1°–

Low

<0.3°

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Land Clutter Backscatter vs. Terrain Type and Frequency

Median Value of σoF (dB)

Frequency Band

Terrain Type

VHF

UHF

L-Band

S-Band

X-Band

URBAN MOUNTAINS FOREST/HIGH RELIEF (Terrain Slopes > 2o) High Depression Angle (> 1o) Low Depression Angle (≤ 0.2o) FOREST/LOW RELIEF (Terrain Slopes < 2o) High Depression Angle (> 1o) Intermediate Depression Angle (0. 4o to 1o) Low Depression Angle (≤ 0.3o) AGRICULTURAL/HIGH RELIEF (Terrain Slopes ≥ 2o) AGRICULTURAL/LOW RELIEF Moderately Low Relief (1o < Terrain Slopes < 2o) Moderately Low Relief (Terrain Slopes < 1o) DESERT, MARSH, GRASSLAND (Few Discretes) High Depression Angle (≥ 1o) Low Depression Angle (≤ 0.3o)

-20.9

-7.6

-10.5 -19.5

-14.2 -26.2

-43.6

-32.4

-27.5

-56.0

-38.2 -66.8

-16.0

-10.6

-16.1 -16.8

-15.7 -29.2

-44.1

-27.3

-30.9

-41.1

-39.4 -74.0

-12.6

-17.5

-18.2 -22.6

-20.8 -28.6

-41.4

-26.9

-28.1

-31.6

-39.6 -68.6

-10.1

-21.4

-23.6 -24.6

-29.3 -32.1

-38.9

-34.8

-32.5

-30.9

-37.9 -54.4

-10.8

-21.6

-19.9 -25.0

-26.5 -29.7

-35.4

-28.8

-28.4

-31.5

-25.6 -42.0

Adapted from Billingsley, Reference 2

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Statistical Attributes of X-Band Ground Clutter

ow

owa σσ 50

Adapted from Billingsley, Reference 2

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Weibull Parameters for Ground Clutter Distributions

103

aw

106

Frequency Bands Resolution(m2)

)dB(owσ

Adapted fromBillingsley, Reference 2

Page 31: Radar 2009 A_10 Radar Clutter1

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L-Band Clutter Experiment Radar

Radar System Parameters

Courtesy of MIT Lincoln LaboratoryUsed with permission

.

Frequency Band (MHz) Antenna Gain (dB) Antenna Beamwidth Az (deg) El (deg) Peak Power (kW) Polarization PRF (Hz) Pulse Width (µs) Waveform A/D Converter Number of Bits Sampling Rate (MHz)

L-Band (1230)

32

6 3

8

HH, VV, HV, VH

500

1

Uncoded CW Pulse

14 2

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Windblown Clutter Spectral Model

( )νtotP

Exponential shapeparameter

( ) ( ) ( )

( ) ( )νβ−β

ν+

+νδ+

exp2

P

P1r

11r

rP

ac

actot

AC spectral power density

Ratio of DC power to AC

power

Doppler velocity in m/s

DC spectral power density

Total spectral power density from a cell containing windblown vegetation

Doppler Velocity (m/s)

North Dakota Cropland (Wheat)Measured Data

P tot

(ν)i

n dB

DCContributionAC

Contribution

Adapted from Billingsley, Reference 2

Page 33: Radar 2009 A_10 Radar Clutter1

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Measured Power Spectra of L-Band Radar Returns from Forest

Curves are hand drawn lines through data in

Billingsley Reference 2

Adapted fromBillingsley, Reference 2

-3 -2 -1 0 1 2 3

Rel

ativ

e Po

wer

(dB

)

-60

-40

-20

0

201-2 mph6-7 mph

18-20 mph

Windy

Light Air

Breezy

LCE RadarRange 7 km

Forest

Wind

Doppler Velocity (m/s)

Page 34: Radar 2009 A_10 Radar Clutter1

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Modeled Rates of Exponential Decay in the Tails of L-Band Spectra from Wind-Blown Trees

( ) ( )νβ−β

=ν exp2

Pac

Exponential shapeparameter

Windy β = 10.7

0L-Band

–20

–60

–40

Rel

ativ

e Po

wer

(dB

)

0 0.5 1.0 1.5

Breezy β= 17.5

Light Air β= 23.5

Doppler Velocity (m/s)

s/m.v 20≥

Exponential decay model agrees very well with measured data

X-Band to L-band–

Variety of wind conditions Light thru heavy wind

Over wide dynamic range > 50 dB

Previously used Gaussian and power law models break down at wide dynamic ranges

Model parameter empirically developed from measured data

[ ]4147.0wlog105.0 101 +=β−

Velocity of wind(statute miles per hour)

β

Adapted fromBillingsley, Reference 2

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Estimated Ground Clutter at Medium Depression Angles (~3 to 70°)

Frequency GHz

=ψψ

σ=γ

o

o

sin

Backscatter Coefficient

Grazing Angle

maxγ Urban0

(dB)

-30

-10

-20

0.2 0.5 1.0 2.0 5.0 10.0 20.0 40.0

Open Woods

Cultivated land

Desert

Curves are Skolnik’sestimates from Nathanson

data (see Reference 6)Many data collections indicate that from ~3 to ~70 degrees is proportional to (Ref 6)oσ ψsin

Page 36: Radar 2009 A_10 Radar Clutter1

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High Depression Angle Ground Clutter

can be large near vertical incidence

In this angle regime the reflected energy is due to backscatter from small flat surfaces on the ground

The total backscatter is the sum of contributions from the different depression angles within the antenna’s beam width

For vertical incidence, measured is at exactly 90°

For an ideal smooth reflecting surface, –

This is a better approximation for smooth sea than typically more rough land (lower for land)

generally > 1 and > than resolution cell size) (see Reference 6)

oσ oσ<

Go ≈σAntenna

Gain

Page 37: Radar 2009 A_10 Radar Clutter1

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Ground Clutter Spectrum Spread Due to Mechanical Scanning of Antenna

Backscatter from ground modulated by varying gain of antenna pattern as beam scans by ground clutter

Ground clutters Doppler spread:

For FAA Airport Surveillance Radar (S-Band, = 10 cm):

Tn265.078.3

clutter

Bclutter

θΩ

==

=θ=Ω

TnB

Antenna rotation rate (Hz)

Antenna beamwidth (radians)

Number of pulses in 3 dB antenna beamwidth

Time between radar pulses (sec)

λ

=θ=Ω

B ==

Tn

1.3°≈σc

1.3°

= 0.023 radians

12.7 RPM, 76.2°/sec 22

0.8 msec.15 Hz

Page 38: Radar 2009 A_10 Radar Clutter1

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Outline

Motivation

Backscatter from unwanted objects

Ground

Sea

Rain

Birds and Insects

Page 39: Radar 2009 A_10 Radar Clutter1

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Figure by MIT OCW.

Attributes of Sea Clutter

Mean sea backscatter is about 100 times less than ground backscatter

Mean cross section of sea clutter depends on many variables–

Radar frequency–

Wind and weather Sea State

Grazing angle –

Radar Polarization–

Range resolution–

Cross range resolution

Sea clutter is characterized by–

Radar cross section per unit area

Aoσ=σ Area Illuminatedby Radar Beam

Sea ClutterRadar Cross Section Grazing Angle (degrees)

σ°-C

ross

sec

tion

per u

nit a

rea

(dB

)

Page 40: Radar 2009 A_10 Radar Clutter1

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World Meteorological Organization Sea State Classification

Sea State Wave Height (m) Wind Velocity (knots) Descriptive Term

0 to 1 0 to 0.1 0 to 6 Calm, Rippled

2 0.1 to 0.5 7 to 10 Smooth, Wavelets

3 0.6 to 1.2 11 to 16 Slight to Moderate

4 1.2 to 2.4 17 to 21 Moderate to Rough

5 2.4 to 4 22 to 27 Very Rough

6 4 to 6 28 to 47 High

Sea State 1 Sea State 3 Sea State 5

Courtesy of NOAA

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Sea Clutter

Environmental parameters–

Wave height–

Wind speed–

The length of time and distance (Fetch) over which the wind has been blowing

Direction of the waves relative to the radar beam–

Whether the sea is building up or decreasing–

The presence of swell as well as sea waves–

The presence of contaminants that might affect the surface tension•

Radar parameters

Frequency–

Polarization–

Grazing angle–

Range and cross range resolution•

The data has “A curse of dimensionality”

The sea backscatter depends on a large number of variables

Adapted from Nathanson, Reference 3

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Nathanson Data Compilation of Mean Backscatter Data

Models compiled from experimental data

Upwind, downwind, and crosswind data averaged over

Adjusted from incidence/depression angle to grazing angle

Median values adjusted to mean values

Monostatic radar data; 0.5–5.9 μs pulse;

Rayleigh distributions

Original data set (1968), 25 references

Present data set (1991), about 60 references

Grazing angles: –0.1°, 0.3°, 1.0°, 3.0°, 10.0°, 30.0°, 60.0°

Adapted from Nathanson, Reference 3

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Normalized Mean Sea Backscatter Coefficient σ0

(dB below 1 m2/m2)

0 V

68*

60*

60*

60*

H 86*

80*

75*

70*

60*

60*

60*1 V 70*

65*

56

53

50

50

48*

H 84*

73*

66

56

51

48

48*2 V 63*

58*

53

47

44

42

40*

H 82*

65*

55

48

46

41

38*3 V 58*

54*

48

43

39

37

34

H 73*

60*

48

43

40

37

364 V 58*

45

42

39

37

35

32

H 63*

56*

45

39

36

34

34*5

V

43

38

35

33

34

31

H 60*

50*

42

36

34

346

V

33

31*

32

H 41 32*

32*

5-dB error not unlikely

Grazing Angle = 1°UHF

L

S

C

X

Ku

Ka/W

Sea State

Polarization

0.5 GHz

1.25

3.0

5.6

9.3

17

35/95

Data Collections and Analyses by NRL underscore this note (See Reference 2, page 15-10)Adapted from Nathanson, Reference 3

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Sea Clutter Reflectivity vs. Grazing Angle

Sea Clutter is independent of polarization and frequency for grazing angles greater than ~45°

In general, backscatter from the sea is less using horizontal polarization than vertical polarization

For low grazing angles and horizontal polarization, the sea clutter backscatter increases as the wavelength is increased

Grazing Angle (degrees)0 10 20 30 40 50 60 70 80 90

-60

-40

-20

0

20

X-

and L-

Band(V &H)

V -

Vertical PolarizationH -

Horizontal Polarization

X-

and L-

Band(V )

L-

Band (V )

X-

Band (V )

X-

Band (H )

L-

Band (H )

220 MHz (H )

50 MHz (H )

σ°-C

ross

sec

tion

per u

nit a

rea

(dB

)

Adapted from Skolnik, Reference 6

Page 45: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 45Clutter 11/1/2009

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Amplitude Distributions

The distributions for sea echo are between Rayleigh and log normal

Log of sea backscatter is normally distributed

Generally, sea echo for HH polarization deviates from Rayleigh more than it does for VV polarization

For a cell dimension less than about 50 m, sea waves are resolved; the echo is clearly non-Rayleigh

The distributions depend on sea state. The echo usually becomes more Rayleigh-like for the higher seas.

For small cells and small grazing angles, sea clutter is approximately log normal for horizontal polarization

Adapted from Skolnik, Reference 6

Page 46: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 46Clutter 11/1/2009

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More attributes of Sea Clutter

Sea clutter has a mean Doppler velocity and spread–

Velocity of waves relative to radar (ship) Wind speed and direction

Sea state

Sea “spikes”–

Low grazing angles–

Short radar pulse widths

Page 47: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 47Clutter 11/1/2009

IEEE New Hampshire SectionIEEE AES Society

Effect of Wind Speed on Sea Clutter

Wind Speed (knots)

4 5 7 10 15 20 30

40 50

σ°-C

ross

sec

tion

per u

nit a

rea

(dB

)

0

-20

-10

-50

-30

-40

+10

X-

Band (V & H) 90°

X-

Band (V & H) 60°

X-

Band (V) 10°

X-

Band (H) 10°

L-

Band (H) 10°

(Various Grazing Angles, Polarizations, and Frequencies)

Adapted from Skolnik, Reference 6

Page 48: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 48Clutter 11/1/2009

IEEE New Hampshire SectionIEEE AES Society

Sea Clutter Effects of the Wind and Waves

σo

increases with increases in wind speed and wave height except at near-vertical incidence

Wind speed and wave height, and wind direction and wave direction are not always highly correlated.

At small grazing angles, σo

is highly sensitive to wave height

At centimeter wavelengths, σo

is highly sensitive to wind speed at the small and intermediate grazing angles

σo

is greatest looking into the wind and waves.–

For small grazing angles, the upwind/downwind ratio is often as much as 5 dB and values of 10 dB have been reported

Adapted from Skolnik, Reference 6

Page 49: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 49Clutter 11/1/2009

IEEE New Hampshire SectionIEEE AES Society

More attributes of Sea Clutter

Sea clutter has a mean Doppler velocity and spread–

Velocity of waves relative to radar (ship) Wind speed and direction

Sea state

Sea “spikes”–

Low grazing angles–

Short radar pulse widths

Page 50: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 50Clutter 11/1/2009

IEEE New Hampshire SectionIEEE AES Society

Sea Spikes

From Lewis and Olin, NRL

•Grazing angle 1.5 deg.•Horizontal polarization

At low grazing angles, sharp sea clutter peaks, known as “sea spikes”, begin to appear

These sea spikes can cause excessive false detections

Figure by MIT OCW.

Page 51: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 51Clutter 11/1/2009

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Sea Clutter Distributions (Low Grazing Angles)

Wind speedLow

Wind speedMedium

Wind speedHigh

AreaOf

Sea Spikes

-50 -40 -30 -20 -10 0 +10 +20

Perc

ent o

f tim

e C

lutte

r Exc

eeds

Val

ue

X-band DataGrazing Angle 3°

Polarization -

Horizontal

σ°

-

Cross Section per unit area (dB)

90

30

50

70

10

5

2

1

Adapted from Skolnik, reference 4

Page 52: Radar 2009 A_10 Radar Clutter1

Radar Systems Course 52Clutter 11/1/2009

IEEE New Hampshire SectionIEEE AES Society

Sea Clutter Summary

Mean backscatter from sea is about 100 times less than that of ground

Amplitude of backscatter depends on Sea State and a number of other factors

Radar wavelength, grazing angle, polarization, etc.

The platform motion of ship based radars and the motion of the sea due to wind give sea clutter a mean Doppler velocity

Sea spikes can cause a false target problem–

Occur at low grazing angles and moderate to high wind speeds