Foliage Penetration Radar - Detection and Characterization of Objects under Trees PDF
Preview Foliage Penetration Radar - Detection and Characterization of Objects under Trees
Foliage Penetration Radar Detection and Characterization of Objects Under Trees Mark E. Davis Raleigh,NC scitechpub.com PublishedbySciTechPublishing,Inc. 911PaverstoneDrive,SuiteB Raleigh,NC27615 (919)847-2434,fax(919)847-2568 scitechpublishing.com Copyright©2011bySciTechPublishing,Raleigh,NC.Allrightsreserved. Nopartofthispublicationmaybereproduced,storedinaretrievalsystemortransmittedinanyformorby anymeans,electronic,mechanical,photocopying,recording,scanningorotherwise,exceptaspermitted under Sections 107 or 108 of the 1976 United Stated Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the CopyrightClearanceCenter,222RosewoodDrive,Danvers,MA01923,(978)750-8400,fax(978)646- 8600,oronthewebatcopyright.com.RequeststothePublisherforpermissionshouldbeaddressedtothe Publisher,SciTechPublishing,Inc.,911PaverstoneDrive,SuiteB,Raleigh,NC27615,(919)847-2434, fax(919)847-2568,[email protected]. Thepublisherandtheauthormakenorepresentationsorwarrantieswithrespecttotheaccuracyorcom- pletenessofthecontentsofthisworkandspecificallydisclaimallwarranties,includingwithoutlimitation warrantiesoffitnessforaparticularpurpose. Editor:DudleyR.Kay EditorialAssistant:KatieJanelle ProductionManager:RobertLawless Typesetting:MPSLimited,aMacmillanCompany CoverDesign:BrentBeckley Printer:SheridanBooks,Inc.,Chelsea,MI Thisbookisavailableatspecialquantitydiscountstouseaspremiumsandsalespromotions,orforuse incorporatetrainingprograms.Formoreinformationandquotes,pleasecontactthepublisher. PrintedintheUnitedStatesofAmerica 10 9 8 7 6 5 4 3 2 1 ISBN:978-1-891121-00-5 LibraryofCongressCataloging-in-PublicationData Davis,MarkE.(MarkEdward),1945- Foliagepenetrationradar:detectionandcharacterizationofobjectsundertrees/MarkE.Davis. p.cm. Includesbibliographicalreferencesandindex. ISBN978-1-891121-00-5(hardcover:alk.paper) 1. Groundpenetratingradar. 2. Forestcanopies. 3. Earth–Surface–Remotesensing. 4. Aerialobservation(Militaryscience) I. Title. TK6592.G7D382011 621.3848’5–dc22 2011005731 ThisDocumentwasApprovedforPublicRelease,DistributionUnlimited,underDISTARCase14973 (2/5/10)andCase15565(5/21/10). Preface The story of foliage penetration RADAR has had many authors over its al- most half century of development. This attempt at reconstructing the early developmentsowesagreatdebttoMrJamesRodems,formerlyofSyracuse University Research Corporation who lead the research, development and earlydeploymentofoneofthetwosystemsinthe1960s.Themajorityofthe materialinChapter1camefromhisarchivesandpersonaldescriptionsofthe motivationandtrialsthatledtobothgroundbasedandairbornetestbed. There were many pioneers in the second phase of FOPEN development during the late 1980s to mid 1990s. But without the continuous support andtechnicalleadershipofDrSerpilAyasliofMITLincolnLaboratory,the breadthofinnovationinphenomenology,waveforms,andimageunderstand- ing would not have matured into today’s solid foundation of science. Two testbeds were developed as independent efforts, each under a strong leader: Stanford Research Institute’s FOLPEN under Roger Vickers, and Swedish DefenceResearchEstableshment’sCARABASunderHansHellsten.Several othertestbedswereconstructedduringthisperiodtoprovidecomplementary geoscienceormilitaryresearchobjectives.Eachoftheairbornetestbedsthat collectedandrefinedtheultrawidebandsyntheticapertureRADARsignals is covered in Chapter 2. They were conceived to implement an important set of innovations, leading to understanding of the importance of frequency choice, polarization, radio frequency interference removal, and target and cluttercharacterizationforefficientdetectionofobjectsunderdenseforests. Much of this development and test was funded by the Defense Advanced Research Projects Agency under the program management of a sequence of leadersthatincludedDomGiglio(1988–1995),MarkDavis(1995–1998)and LeeMoyer(1999–2005). Modern foliage penetration RADAR continues to advance with the con- tinuousimprovementinhighspeeddigitalsignalprocessing.Thesinglemost impediment to its general use is the proliferation of personal and wideband communicationsintotheradiofrequencyspectrum.Frequencyspectrumallo- cationandprotectionofspecificfrequenciesforsafetyoflifeandemergency ix x Preface communicationsrequirescarefulattentiontothechoiceofwaveform.Itwill continuetobeimportanttodevelopcognitiveprocessingtoavoidinterference toorfromotherusersofthisspectrum. Theauthorwouldliketoacknowledgeallofthepioneerswhopreceeded andsucceededhisinvolvementinfoliagepenetrationradardevelopment.The past15yearshasbeenaveryenjoyablejourneyintothescientificandgeopolit- icalevolutionofultrawidebandradar.Hewouldalsoliketothankhisparents, Jack and Mary Lou Davis for encouraging his scientific development. And mostimportantlyhewouldliketothankhiswifeDianeRogersDavis,andtwo sonsColinandShelbyforthepatienceandencouragementinalongjourney intoRADARdevelopment,testandoperation. MarkE.Davis [email protected] March2011 Contents Preface ix Chapter1 HistoryofBattlefieldSurveillance 1 1.1 EarlyFOPENMTIRADAR 5 1.2 SyntheticApertureDualFrequencyRADAR 16 1.3 Summary 20 1.4 References 22 Chapter2 FoliagePenetrationSARCollectionSystems 23 2.1 SARResolution 27 2.2 FOPENSARSystems 31 2.3 References 54 Chapter3 FoliagePenetrationPhenomena 57 3.1 FoliagePhaseEffectsonRADARPropagation 60 3.2 StandardCalibrationforFOPENMeasurements 65 3.3 StandardRCSTargetCharacteristics 69 3.4 FoliageClutterScatteringCharacteristics 78 3.5 FoliageAttenuation 86 3.6 InternalClutterMotion 89 3.7 TargetCharacteristics 92 3.8 RadioFrequencyInterferenceSpectrum 96 3.9 References 99 Chapter4 FOPENSARImageFormation 101 4.1 FOPENSARCollectionGeometry 102 4.2 FOPENSARWaveform 109 4.3 SARImageFormation 122 4.4 SARMotionCompensation 132 4.5 References 140 Chapter5 RadioFrequencyInterferenceSuppression 143 5.1 TransmitWaveformDesignforRFIEnvironment 146 5.2 CancellationofRadioFrequencyInterference 166 vii viii Contents 5.3 RFISuppressionSummary 183 5.4 References 184 Chapter6 FOPENTargetDetectionandCharacterization 187 6.1 TargetDetectionProcessing 188 6.2 PolarimetricScattering 195 6.3 TargetCharacterization 204 6.4 RADCONProcessingDevelopment 208 6.5 ChangeDetection 213 6.6 FOPENATD/CSummary 222 6.7 References 223 Chapter7 FOPENSARDesign 227 7.1 ConceptofOperations 228 7.2 FOPENSARHardware 234 7.3 FOPENSARSystemDesign 260 7.4 References 270 Chapter8 FOPENGroundMovingTargetIndication 273 8.1 FOPENGMTIRADARDesign 274 8.2 Space-TimeAdaptiveProcessing 279 8.3 Along-TrackInterferometry 289 8.4 References 313 Chapter9 BistaticFOPENSAR 315 9.1 BistaticRADAR 317 9.2 BistaticSARSignalGeometry 322 9.3 BistaticSARResolution 325 9.4 BistaticSARModeling 333 9.5 Summary 343 9.6 References 344 Glossary 345 Index 353 CHAPTER 1 History of Battlefield Surveillance 1.1 Early FOPEN MTI RADAR........................................5 1.2 Synthetic Aperture Dual Frequency RADAR.......................16 1.3 Summary.......................................................20 1.4 References ..................................................... 22 Themilitaryhaslongknownoftheimportanceofsurveillanceonthebattle- field.Thedevelopmentoftheballoonpriortothe1861AmericanCivilWar,as illustratedinFigure1–1,gavethecommanderonthegroundtheabilitytosee longer distance and with more safety than any forward ground observer [1]. SincethemilitaryhadmoreaccesstoballoonsandtheearlyairplaneinFirst World War, the opposing side obviously sought a counter to this battlefield surveillancecapability. Often, airborne surveillance was opposed simply by hiding in woods to denytheothersideanaccurateknowledgeofone’stacticalintent.However, when these surveillance platforms were given weapons, the ensuing counter was to shoot at the platforms from the ground position. An alternative to offensive retaliation was to exploit a natural obscurant such as maneuvering inthefogorrainorcreatingasmokescreentodenylong-rangesurveillance. Until RADAR was developed, armies of the world successfully employed tactics of concealment and deception to deny their adversaries the current knowledgeoftheirpositionandmaneuvertactics. In 1903, Christian Hu¨lsmeyer conducted the first experiments using RADARbyscatteringradiowavesoffships;andhispatentfollowedin1904. However,atthattimetheGermanmilitarydidnotsupporthisworkbecause itconsideredradiowavecomponentstobestillunderdeveloped.AsSkolnik pointsout,RADARdidnotgeneratemuchscientificinterestuntilthe1920s and1930s[2].Marconi’sresearchaswellasdevelopmentsattheNavalRe- searchLabdemonstratedtheabilitytodetectshipsonthesurfaceandaircraft intheair.Bothlong-waveandmicrowaveRADARwerebeingdevelopedin EuropeandtheUnitedStates.BythestartoftheSecondWorldWar,RADAR technology had progressed sufficiently to detect aircraft and ships at long rangesfromgroundinstallations.SoonaircraftwerebeingprovidedRADARs 1 2 HistoryofBattlefieldSurveillance FIGURE1--1 Battlefieldsurveillancein1861[1] for all weather detection of air and ground targets. However, ground clutter (especially forests) was a significant problem to early airborne RADARs, sinceitcompetedwithdetectionoftargets,orconcealedthoseobjectshidden under the clutter. No real attempts were made to image or penetrate this ob- scurationfordetectingobjects,primarilyduetothelackofstablewaveform andsignalprocessingtechnology. Intheearly1960s,theUSArmydevelopedthefirstbattlefieldsurveillance RADAR—theOV-1APS-94side-lookingarrayRADAR(SLAR),whichwas fordetectingmilitaryencampmentsandlargegroupsofartilleryandmecha- nizedvehiclesonthebattlefield[3].Intheearly1970s,thearmydetermined that there was also a need for detecting large numbers of moving vehicles, at a significant range from the forward edge of the battle area (FEBA). The first ground moving target indication (GMTI) system for battlefield surveil- lance was developed as the standoff target acquisition system (SOTAS). It was constructed using the APS-94 RADAR with a moving target mode and operatedfromaUH-1helicopter.Thehelicopterwasnecessarytominimize theplatformmotionandtoprovidesufficientlylowminimumdiscernableve- locity(MDV)detectionsoverawidearea.TheSOTASprototypewastested in the United States and in Germany under the return of forces to Germany HistoryofBattlefieldSurveillance 3 FIGURE1--2 SOTASRADARduring1980REFORGERdeployment[4] (REFORGER)exercises,asshowninFigure1–2,andwasacceptedbymilitary leadersasacapableoperationalcapability.Becauseofthedemonstratedim- portanceofdetectingslowlymovingtroopsatlongdistance,thearmystarted todevelopanoperationalsystemtobeinstalledonaBlackHawkUH-60heli- copter.TheBlackhawkhadalargercapacitypayloadandalongerendurance thantheUH-1.Butthesystemdevelopmentwasstoppedin1978bytheSec- retaryofDefensebecauseevenlongerenduranceandmoresurvivabilityofa mannedplatformwereneeded[5]. The battlefield surveillance capabilities of SLAR and SOTAS soon led to the development of the Joint Surveillance and Target Acquisition sys- tem (JOINT STARS) for use by the army and air force [5]. The JOINT STARS standoff battlefield surveillance capabilities could be integrated on a high-altitude, multiengine aircraft for longer endurance and significantly longer standoff for survivability. The benefits of JOINT STARS combining SARandGMTIonthebattlefieldareextensivelydocumentedandhavebeen reproducedandfieldedonmanyinternationalplatforms.Alltheseearlybat- tlefield surveillance RADAR systems were developed in the microwave fre- quencyband.Microwavefrequencieswereimportanttoprovideall-weather, long-range, high-probability detection of vehicles and structures and to allow systems to be small enough that they could be carried on tactical aircraft[6]. However,therewasoneimportantoperationalissue—theopposingcom- batantsunderstoodX-bandRADAR’slimitationstoseethroughforestcover. TacticshadbeendevelopedtodenymicrowaveRADARstheabilitytoimage movementandlocategroundforces.Hidingintreelinesandusingotherforms 4 HistoryofBattlefieldSurveillance ofcamouflageandconcealmentquicklycounteredoperationalRADAR.This concealmenttactichadbecomehighlyeffectiveagainstRADAR,asithadfor earlyopticalsurveillance.Thus,therewasanevolvingneedtodetectfixedand movingtargetsunderfoliage,asacomplementtotheverycapablemicrowave battlefieldsurveillanceRADARsystems. Thefirstdevelopmentoffoliagepenetration(FOPEN)RADARoccurred during the Vietnam conflict, where early systems were needed to detect and recognize ground-moving targets [7]. Specifically, there was a compelling need to detect and locate insurgent soldiers walking through the dense trop- ical forests. Two innovations were needed: (1) coherent waveforms and the associatedsignalprocessing;and(2)RADARinstallationsonmajorhillsand masts. These two innovations increased the target signal-to-noise and min- imized the clutter spread that masked the small returns from personnel and vehicles. However, it did not provide any ability to detect stationary, man- madeobjects.AparalleldevelopmentofFOPENsyntheticapertureRADAR (SAR)wasneededtodetectman-madeobjectsunderthetrees.Therequired technology innovations for foliage penetration SAR were wideband image processingandcoherentdiscriminationofman-madeobjectsfromtheback- groundclutter. FOPENRADARhascontinuedtobeadevelopingtechnologytoprovide geospatial and military users with detection and characterization of objects underdensefoliage.Manyareasoftheearthareremoteandinhospitablefor characterization,aswellasmonitoringtheeffectsofweather,atmosphereand geological changes on the region. Similarly, military commanders want to know about recent construction or tactical maneuvers in an area covered by densefoliage.RADARhastheinherentabilitytocharacterizeawidearea,to assesschangesinfixedobjects,andtodetectandtrackmovingobjects.Early RADARswerelimitedtodetectionandtrackingofobjectsbytheattenuation andscatteringofclutterbetweentheRADARandthefeaturesbeingobserved. Forestshavebeenparticularlydifficultenvironmentsduetothescatteringof thewaveformsandsevereattenuationatmicrowavefrequencies. Over the past 40 years, the advances in waveform synthesis and digital signal processing have given the RADAR community the ability to observe thebehavioroffixedandmovingobjectsunderfoliage.Themostsignificant advancewasinsynthesisandreceptionofultra-widebandwaveforms,where the signals can achieve over 50% fractional bandwidth. Digital signal pro- cessing enables the RADAR to compensate for scattering of the signal by the foliage and to discriminate the man-made objects from the surrounding clutter. However, before the details of these innovations are explored, it is beneficial to trace the history and early motivation for foliage penetration RADAR.
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