Application of SeaWinds Scatterometer Data to the Study of Antarctic Icebergs Keith M. Stuart A ...

171 Pages·2012·4.48 MB·English

by  Keith M. Stuart

ApplicationofSeaWindsScatterometerDatatotheStudyofAntarcticIcebergs
KeithM.Stuart
Adissertationsubmittedtothefacultyof
BrighamYoungUniversity
inpartialfulfillmentoftherequirementsforthedegreeof
DoctorofPhilosophy
DavidG.Long,Chair
RichardW.Christiansen
DavidJ.Comer
DahJyeLee
JulieC.Vanderhoff
DepartmentofElectricalandComputerEngineering
BrighamYoungUniversity
December2012
Copyright©2012KeithM.Stuart
AllRightsReserved
ABSTRACT
ApplicationofSeaWindsScatterometerDatatotheStudyofAntarcticIcebergs
KeithM.Stuart
DepartmentofElectricalandComputerEngineering
DoctorofPhilosophy
Knowledge of iceberg location and size is important for safety reasons as well as for
understanding many geophysical and biological processes. This dissertation analyzes large tab-
ular icebergs in the Southern Ocean using the SeaWinds scatterometer. SeaWinds is a space-
borne radar designed to measure the microwave backscatter from the Earth’s surface. Using
resolution-enhancement techniques, backscatter measurements are processed into backscatter im-
agesinwhichicebergscanbeobserved.
An iceberg detection methodology is formalized using daily scatterometer images. Radar
profiles from common Antarctic scatterers are quantified and an iceberg detection methodology is
formalized using daily scatterometer images. Iceberg positions are determined in real-time and a
time-seriesoficebergpositionsismaintainedinanAntarcticicebergdatabase. UsingtheAntarctic
iceberg database, characteristic iceberg motion trends are identified. Iceberg detection and track-
ing is demonstrated through real-time operational support of the 2005, 2008, and 2009 National
ScienceFoundationAntarcticcruises.
To supplement iceberg position reports, I develop multiple algorithms to estimate iceberg
size and rotational orientation from backscatter images and from raw backscatter measurements.
Estimates derived from SeaWinds images are found to be more accurate. Using iceberg size pa-
rametersinconjunctionwithNewton’sequationsofmotionandforcingprofiles(e.g.,oceanandair
currents),Ialsodevelopanicebergmotionmodeltopredictthetranslationalandrotationalmotion
of large tabular icebergs. To improve model results, a Kalman filter is used to incorporate actual
icebergmeasurementsintothemotionmodel,andstatisticsfromtheKalmanfilterareusedtoeval-
uatemodelperformance. Simulatedicebergmotionisfoundtobestcoincidewithobservediceberg
motion in regions where slower iceberg drift speeds are observed. The model is less accurate at
highspeeds.
Theicebergmotionmodelisinvertedtoproduceestimatesofoceancurrentsgivenobserva-
tionsoficebergsizeandmotion. Multipleoceancurrentestimatesarecombinedusingreconstruc-
tiontechniquesandcomparedwithnumerically-derivedoceancurrentsfromtheOceanCirculation
and Climate Advanced Modeling (OCCAM) project. It is found that reconstructed ocean currents
coincide with OCCAM currents in regions where observed iceberg motion is not extreme. Also,
reconstructed ocean currents coincide more with OCCAM currents that have been averaged over
multipleyearsthanwithmonthly-reportedvalues.
Keywords: SeaWinds,scatterometer,iceberg,SouthernOcean
ACKNOWLEDGMENTS
Iwouldliketothankthemanyteachersandmentorswhohaveinspired,guided,andshown
me that there are always wonderful things to explore. I acknowledge the guidance of Dr. David
Long,myacademicadviserwhointroducedmetothefieldofremotesensing.
I would also like to thank the National Science Foundation for their support of the 2005,
2008, and 2009 Antarctic cruises as well as the officers, crew, and scientists aboard the first cruise
ARSV L.M. Gould cruise LMG05-014A and the second and third cruises RVIB N.B. Palmer,
NBP08-06andNBP09-02,fortheirhardworkatsea.
Mostofall,Iacknowledgemywife,JessicaStuart,whosesupportandencouragementhas
madethisworkpossible.
Table of Contents
ListofTables ix
ListofFigures x
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 PreviousWork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.1 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2.2 Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.3 Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4 ResearchContributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2 Background 10
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 SeaWinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 ResolutionEnhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 DetectingIcebergs 17
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
iv
3.2 SeaWindsBackscatterImages . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.3 ScatteringTheory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4 AntarcticBackscatterProfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.5 IcebergDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.5.1 DetectionMethodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.5.2 NRTIcebergDetection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4 TrackingIcebergs 29
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2 IcebergDatabase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 IcebergCounts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.4 IcebergMovementProfiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.5 CaseStudyofIcebergC19a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.6 NSFCruiseCaseStudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.6.1 The2005Cruise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.6.2 The2008Cruise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.6.3 The2009Cruise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.6.4 SampleData . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5 EstimatingIcebergSizeandOrientation 47
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3 IcebergModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
v
5.4 EstimationAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4.1 Image-basedEstimation . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.4.2 Measurement-basedEstimation . . . . . . . . . . . . . . . . . . . . . . . 53
5.4.3 AlgorithmComparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.5 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.5.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.5.2 CaseStudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.5.3 Time-series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6 EstimatingIcebergMotion 76
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
6.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.2.1 ClimatologicalDatasets . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.2.2 IcebergDatasets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6.3 IcebergModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.4 EstimationAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.4.1 EquationsofMotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.4.2 NumericalIntegration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.4.3 DataAssimilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6.5 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.5.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.5.2 CaseStudy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.5.3 DataAssimilation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
vi
6.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
7 EstimatingOceanCurrents 121
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.2 Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.2.1 IcebergMotionModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.2.2 PhysicalIcebergModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.2.3 OceanModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.3 EstimationAlgorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.3.1 IcebergTracksSimulation . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.3.2 OceanCurrents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
7.4 Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
7.4.1 IcebergTracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
7.4.2 OceanCurrents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
8 Conclusion 140
8.1 SummaryofContributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
8.2 FutureWork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Bibliography 144
A MapoftheSouthernOcean 152
B AReviewofMicrowaveScatteringfromAntarcticTargets 154
B.1 SurfaceandVolumeScattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
vii
B.2 AntarcticScatterers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
B.2.1 SeaWater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
B.2.2 SeaIce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
B.2.3 GlacialIce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
C DragonanIcebergduetoInternalOceanWaves 158
viii
List of Tables
3.1 Expectedbackscatterfromseawater,seaice,andglacialice . . . . . . . . . . . . 23
4.1 IcebergcountsreportedtotheNSFAntarcticcruises . . . . . . . . . . . . . . . . 34
4.2 Icebergsdetectedduringthe2005NSFAntarcticcruise . . . . . . . . . . . . . . . 36
4.3 Icebergsdetectedduringthe2008NSFAntarcticcruise . . . . . . . . . . . . . . . 39
4.4 Icebergsdetectedduringthe2009NSFAntarcticcruise . . . . . . . . . . . . . . . 42
5.1 Icebergsizeestimationsimulationresults . . . . . . . . . . . . . . . . . . . . . . 56
5.2 Comparisonofsizeestimateswithvariableregularization . . . . . . . . . . . . . . 58
5.3 Resultsofsizeestimationalgorithms . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.4 Differencesbetweenicebergsizeestimatesandhigh-res. imageryestimates . . . . 65
5.5 CountofaccuratesizeestimatesoficebergA22a . . . . . . . . . . . . . . . . . . 70
7.1 RMS differences between averaged iceberg-derived ocean currents and averaged
OCCAMcurrents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
7.2 Averageiceberg-basedandOCCAMsurfacecurrentvelocities . . . . . . . . . . . 133
7.3 RMSdifferencesbetweendailyiceberg-derivedoceancurrentsanddailyOCCAM
currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
7.4 RMS differences between daily iceberg-derived ocean currents and averaged OC-
CAMcurrents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
ix
List of Figures
2.1 SeaWindsscanninggeometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 SeaWindsfootprintgeometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 SamplebackscatterimageofAntarctica . . . . . . . . . . . . . . . . . . . . . . . 15
2.4 SamplebackscatterimageoftheWeddellSea . . . . . . . . . . . . . . . . . . . . 16
3.1 BackscatterimagesofSouthGeorgiaIsland . . . . . . . . . . . . . . . . . . . . . 19
3.2 BackscatterimageoftheRossSea . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3 Backscatterhistogramsofseawater,seaice,andglacialice . . . . . . . . . . . . . 23
3.4 Multi-daybackscatterhistogramsofseawater,seaice,andglacialice . . . . . . . 24
3.5 Expectedbackscatterfromseawater,seaice,andglacialice . . . . . . . . . . . . 25
3.6 AverageannualseaiceextentintheSouthernOcean . . . . . . . . . . . . . . . . 26
4.1 IcebergcountusingSeaWinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 IcebergtracksdetectedusingSeaWinds . . . . . . . . . . . . . . . . . . . . . . . 32
4.3 Time-seriesofbackscatterimagesoficebergC19a . . . . . . . . . . . . . . . . . 34
4.4 Icebergsdetectedduringthe2005NSFAntarcticcruise . . . . . . . . . . . . . . . 37
4.5 Icebergsdetectedduringthe2008NSFAntarcticcruise . . . . . . . . . . . . . . . 40
4.6 Icebergsdetectedduringthe2009NSFAntarcticcruise . . . . . . . . . . . . . . . 41
4.7 SampleNRTicebergupdateimages . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.8 ValidationimagesoficebergC19a . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.9 ValidationimagesoficebergA22a . . . . . . . . . . . . . . . . . . . . . . . . . . 46
x