RadarSignaturesofSmallConsumerDrones

ChenchenJ.LiandHao LingTheUniversityofTexasatAustin

1

• The proliferation of small consumer drones has raisedmuch recent interest in their regulation and monitoring.

• One potential way to detect and identify these drones isusing a ground-based radar.

• Objective: To investigate the radar signatures of thesesmall drones.

2

MotivationandObjective

DJIPhantom 3DRSolo DJIInspire

• Carryoutlaboratorymeasurementofsmallconsumerdrones.• Examinetheirradarsignaturesintheformofinversesynthetic

apertureradar(ISAR)images.• ISARimagingprovidesnotonlyradarcrosssection(RCS),but

alsomapsthedominantscatteringin2-D.

ScientificQuestions:1. Willthesmallsizeandlowreflectivityofthedronebody

resultinaverylowRCS?2. Willthespinningpropellerbladesresultinsignificant

Dopplerartifacts[1]?

3

Approach

[1]P.Pouliguen etal., IEEETrans.AntennasPropagat.,2002.

• Vectornetworkanalyzer(VNA)S11 measurement.• Dronemountedandrotatedonaturntable.• Startwithbaselinescenarioandthendeviate.• CalibratedresultsintermsofabsoluteRCSusinga

calibrationsphere.• Hornmismatchandroomclutterarereducedby

subtractingthemovingaverage.• 3GHzofbandwidth.

– 5cmofdown-rangeresolution.

4

LaboratoryMeasurementSetup

• 2-Dimagegeneratedusing2-DinverseFouriertransformoffrequency/angledata.

• Angularswathchosenforequaldown-range/cross-rangeresolutionof5cm.

• SlideswathalongangletogenerateanISARmovie.

5

ISARImageFormation

Polar->Rect.2-DIFFT

Frequencyresponse

Freq

uency

RotationAngle(orTime)

ISARimage

Down-range

Cross-range

Swath

𝐼𝑚𝑎𝑔𝑒 𝑟, 𝑐𝑟 =1

𝐾,𝐾-.𝐸0 𝑓, ϕ

�

�𝑒4567𝑒45897𝑑𝑘,𝑑𝑘-

𝑤ℎ𝑒𝑟𝑒𝑘, =

4𝜋𝑓𝑐 cos ϕ

𝑘- =4𝜋𝑓𝑐 sinϕ

• DJIPhantom2(35cmdiagonal).• Azimuthscanatzero-elevationangle:resultsinatop-viewof

thedrone.• 12-15GHz,bladesstationary,VV-pol,nocamera.

6

BaselineScenario

θ"#θ$%

ISARmovieavailableat:http://users.ece.utexas.edu/~ling/DroneISARMovie.gif

• ISARimagesnapshotsatdifferentlookangleswithanoutlineofdroneoverlaid.

• MaximumRCSineachsnapshotislisted.

7

ISARSnapshots

Max=-13.8dBsm

EL=0°,AZ=8°

Max=-19.4dBsm

EL=0°,AZ=45°

Max=-9.3dBsm

EL=0°,AZ=90°

Max=-18.8dBsm

EL=0°,AZ=135°

Max=-16.3dBsm

EL=0°,AZ=172°

8

DeviationsFromBaseline

BaselineScenario

BladesSpinning

FrequencyChange

PolarizationChange

MountedCamera

ElevationScan

LargerDrones

• Nosignificantdifferencesbetweenbladesrotatingandstationary.

• Onaverage,RCSat3-6GHzabout~12dBlowerthan12-15GHz.

9

DeviationsFromBaseline

Max=-14.6dBsm

EL=0°,AZ=102°

Max=-15.3dBsm

EL=0°,AZ=102°

BladesStationary BladesSpinning

Max=-17.2dBsm

EL=0°,AZ=194°

Max=-27.5dBsm

EL=0°,AZ=194°

12-15GHz 3-6GHz

Rotatin

gBlades

Freq

uencyCh

ange

• HH-Pol:weakerbatteryreturn,strongermotorreturn.

• Cameracanonlybeseenatspecificlookangles.

10

DeviationsFromBaseline

Max=-12.0dBsm

EL=0°,AZ=60°

Max=-12.0dBsm

Camera

EL=0°,AZ=60°

WithoutCamera WithCamera

Max=-13.5dBsm

EL=0°,AZ=6°

Max=-15.3dBsm

EL=0°,AZ=6°

VV-Pol HH-Pol

PolarizationCh

ange

CameraMou

nted

• Elevationscan insteadofazimuthscan.• Capturestheshapeofthedroneinanotherimagingplane.• Insteadoftop-viewofthedrone,capturedtheside-view.• Inpractice,collectedbyflippingdroneonitssideandrotating.

11

DeviationsFromBaseline

Max=-9.0dBsm

EL=-90°,AZ=0°

Max=-9.3dBsm

EL=0°,AZ=90°

AzimuthScan ElevationScan

• Droneshapeandsizecaptured.

• MaximumRCSsmallerthanPhantom2duetobodyshape.

• SimilartrendsasPhantom2.

12

LargerDrones:3DRSolo3DRSolo(46cmdiagonal)

Max=-14.1dBsm

EL=0°,AZ=90°

12-15GHz

Max=-24.2dBsm

EL=0°,AZ=90°

3-6GHz

• Droneshapeandsizecaptured.

• Additionalfeaturefromthehorizontalframe.

• HighestmaximumRCSofthethreedrones.

• SimilartrendsasPhantom2and3DRSolo.

13

LargerDrones:DJIInspire1DJIInspire1(56cmdiagonal)

Max=-3.0dBsm

EL=0°,AZ=270°

12-15GHz

Max=-13.7dBsm

EL=0°,AZ=270°

3-6GHz

• OverallRCSlevelislow,butthedronesizeandshapecanbecaptured intheISARimagery.

• Non-plasticportionsdominatetheirradarsignatures(suchasmotors,batterypack,andcarbon-fiberframe).

• Dronepropellersdidnotcontributeasignificantreturnrelativetothedronebody(staticorspinning).

• Datacollectionwasunderidealizedconditions,butitshouldbefeasibletocollectsuchdatafromanactualdroneinflight.

• Next:Carryoutin-flightmeasurementofthesmalldrone.• ScientificQuestion:CanfocusedISARimagesbegenerated

fromthesesmalldronesinflight?

14

Recap

• PulsON 440(P440)ultra-wideband(UWB)radarbyTimeDomainCorporation.

• Emitsshortpulsesatapulserepetitionfrequencyof10MHz.

• Equivalentfrequencybandwidthfrom3.1to5.3GHzcenteredat4.3GHz.

15

In-SituMeasurementUsingaUWBRadar

• MeasurementsetuponthegroundincludesP440radar,circulator,andsinglehornantenna.

• Phantom3Adv.isusedsinceithasextractableGPSflightdata.• Collectrangeprofiles(at100Hz) asthedronefliesbyina

straightline.

16

In-FlightMeasurementSetup

• Motioncompensationisnecessarytoremovetranslationalmotionandretainonlytherotationalmotion.

• Imagesgeneratedthroughblindmotioncompensation(alignmentoftheRCScentroid).

• Baselineimagesalsogeneratedwithaidfrom“groundtruth,”GPSflightdata.

• Angleestimatebasedonϕ = cosGH(𝑅/𝑅LMN).Imagesformedusingsamek-spaceimagingasbefore.

17

MotionCompensation

Dow

n-ra

nge

(m)

Time (s)

0.5 1 1.5 2 2.5 3

7.5

8

8.5

9

9.5

10

10.5

11

-30

-25

-20

-15

-10

-5

0

Dow

n-ra

nge

(m)

Time (s)

0.5 1 1.5 2 2.5 3-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

-30

-25

-20

-15

-10

-5

0

RawRangeProfiles AfterMotionComp.

• Imagesobtainedfromblindmotioncompensationareon-parwithimagesobtainedfromGPS-assistedmotioncompensation.

• Imagesarefocusedbutnarrowerbandwidthofradarandlimitednumberofscatterers onthedronemakeitchallengingtodiscerntheshape.

18

Phantom3Adv.ResultsGPS-AssistedMotionCompensation

AZ=270°

BlindMotionCompensation

AZ=270°

19

LargerDrone:DJIInspire1

ISARmovieavailableat:http://users.ece.utexas.edu/~ling/DroneISARMovie_Inspire.gif

20

ComparedtoLaboratoryMeasurement

AZ=270°

LabMeas.(3-6GHz)

Max=-13.7dBsm

EL=0°,AZ=270°

In-SituMeas.(3.1-5.3GHz)

Imagesafterblindmotioncompensationarecomparabletothoseobtainedinlaboratorymeasurement.

21

ComparedtoPhantom3

AZ=270°AZ=270°

In-situMeas.Phantom3In-situMeas.Inspire1

Sizedifference,fromPhantom3,isobserved.

• ISARimagescancapturethedroneshapeandsizedespiteitssmallsizeandlowreflectivity.

• SpinningpropellersdonotcontributesignificantDopplerclutter.

• Focusedimagescanbegeneratedfromin-flightmeasurement.

• Radarisapotentialcandidatefortrackingandclassificationofsmallconsumerdrones.

22

Conclusion

23

Acknowledgment

ColtonBostick ofUAVDirectandLennyTropiano ofFlyTheSkyDrone Productionsforprovidingdronesformeasurement.

AlanPetroffofTimeDomainCorporationfortechnicalsupportontheultra-widebandradar.

ThisworkwassupportedinpartbytheNationalScienceFoundationunderGrantECCS-1232152.