Radar Altimeter General Waveform Model and Its Application to Cassini Mission

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    Radar Altimeter General Waveform

    Model and Its Application to Cassini

    Mission

    by

    Guido Vingione

    Department of Aerospace and Mechanical Engineering,

    Second University of Naples, Aversa

    Italy

    November 2007

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    Radar Altimeter General Waveform Model and Its Application to Cassini Mission 3

    TABLE OF CONTENTS

    TABLE OF CONTENTS.....................................................................................................3

    TABLE OF FIGURES.........................................................................................................5

    ABSTRACT..........................................................................................................................7

    ABSTRACT (ITALIANO) ................................................................. .................................9

    ACKNOWLEDGMENTS ....................................................... ..........................................11

    ABBREVIATION ........................................................... ...................................................12

    1 INTRODUCTION........................................................... .........................................14

    2 SATELLITE ALTIMETRY....................................................................................20

    2.1 OVERVIEW OF THE RAMISSIONS.......................................................................20

    2.2 ALTIMETRY PRINCIPLES AND TECHNIQUES........................................................22

    2.2.1 Off-Nadir Altimeter Technique.....................................................................26

    2.2.2 RA Spatial Resolution.......................................................... .........................28

    2.2.3 RA Accuracy......................... ................................................................ ........32

    3 RADAR ALTIMETER WAVEFORM MODELS.................................................42

    3.1 RANADIR LOOKING..........................................................................................42

    3.1.1 Nadir FSIR Evaluation.......................... .......................................................42

    3.1.2 Nadir IR Evaluation ......................................................... ............................45

    3.1.3 MLE Algorithm.......................................................................... ...................51

    3.1.4 Evaluation of Gating Functions for Nadir Pointing Model..........................54

    3.1.5 Model Implementation and Results ..............................................................57

    3.2 RAOFF-NADIR POINTING..................................................................................60

    3.2.1 Off-Nadir FSIR Evaluation ........................................................... ...............62

    3.2.2 Off-Nadir IR Evaluation...............................................................................70

    3.2.3 Evaluation of Gating Functions for Off-Nadir Pointing Model ...................70

    3.2.4 System of Gating Functions for Off-Nadir Models.......................................76

    3.2.5 Model Implementation and Results ..............................................................77

    3.3 OFFNADIR IRALGORITHM BY PRONYS METHOD ............................................78

    3.3.1 Near Off-Nadir IR Evaluation ............................................................... .......78

    3.3.2 Evaluation of Gating Functions for Off-Nadir Prony Model .......................80

    3.3.3 Model Implementation and Results ..............................................................81

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    Radar Altimeter General Waveform Model and Its Application to Cassini Mission 4

    3.4 INTERFEROMETRIC APPROACH ..........................................................................84

    3.5 ALTIMETER MODELS VALIDATION ALGORITHM................................................92

    3.5.1 Simulation Algorithm .............................................................. .....................923.5.2 Comparison with numerical solutions........................................................100

    4 CASSINI ALTIMETER DATA PROCESSING ALGORITHMS.....................105

    4.1 THE CASSINI RADAR........................................................................................106

    4.2 CASSINI PADSYSTEM OVERVIEW...................................................................106

    4.3 CASSINI ALTHMODELS IMPLEMENTATION ....................................................111

    4.4 CASSINI MODEL IMPLEMENTATION:FINAL CONSIDERATIONS ..........................114

    5 CONCLUSIONS.....................................................................................................123

    APPENDIX A PRONYS APPROXIMATION METHOD.......................................125

    APPENDIX B AUTHORS PUBBLICATIONS..........................................................127

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    Radar Altimeter General Waveform Model and Its Application to Cassini Mission 5

    TABLE OF FIGURES

    FIGURE 1GEOMETRY OF A NADIR ORIENTED (A)BEAMWIDTH-LIMITED ALTIMETER (DP>DB)

    AND (B)PULSEWIDTH-LIMITED ALTIMETER (DP

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    Radar Altimeter General Waveform Model and Its Application to Cassini Mission 6

    KM) .......................................................... ........................................................... .........83FIGURE 38ESTIMATIONS OF COGPOSITION OVERN=100RUNS (BURST #14364)................84FIGURE 39INTERFEROMETRICAPPROACH GEOMETRY.........................................................85FIGURE 40FSIRFOR THE INTERFEROMETRIC CONFIGURATION FOR BASELINE VALUES OF

    (FROM UP TO DOWN)6,8AND 10METERS. ........................................................... .........87FIGURE 41FSIRFOR THE INTERFEROMETRIC CONFIGURATION FOR OFF-NADIR ANGLE VALUES

    OF (FROM UP TO DOWN)2,4AND 6DEGREES. ...................................................... .........88FIGURE 42NUMBER OF LOBES WITHIN A SPECIFIED APERTURE.............................................90FIGURE 43NUMBER OF LOBES WITHIN A SPECIFIED APERTURE.............................................91FIGURE 44RANGE COMPRESSEDDATA SIMULATIONALGORITHM.........................................93FIGURE 45MODELS VALIDATIONALGORITHM.....................................................................95 FIGURE 46SIMULATEDRANGE COMPRESSEDBURST............................................................96FIGURE 47SIMULATEDRANGE COMPRESSEDBURST:PULSEZOOMIN.................................96FIGURE 48AVERAGEDRANGE COMPRESSEDBURST.............................................................97FIGURE 49AVERAGEDRANGE COMPRESSEDBURST:ZOOMIN.............................................97FIGURE 50EXAMPLE OFEVALUATED WAVEFORM................................................................98FIGURE 51COMPARISON BETWEEN EVALUATED WAVEFORM (LEFT)AND WAVEFORM

    SIMULATING THE SPECKLE............................................................................................98 FIGURE 52EXAMPLE OF SIMULATED TOPOGRAPHY SHAPE...................................................99FIGURE 53ESTIMATED TOPOGRAPHY..................................................................................99 FIGURE 54ERROR IN METERS [ABS(SIMULATED TOPOGRAPHY-ESTIMATED TOPOGRAPHY)] 100FIGURE 55MODELSAPPLICABILITYDIAGRAM...................................................................101 FIGURE 56CASSINIMLEALGORITHM IMPLEMENTATION....................................................113FIGURE 57CASSINI T3RANGE COMPRESSEDPULSE #65016572........................................115 FIGURE 58MLEBEST FITTING PROCESS:1STSTEP..............................................................115FIGURE 59MLEBEST FITTING PROCESS:LAST STEP...........................................................116FIGURE 60MLEBEST FITTING PROCESS:ERROR CONVERGENCE. .......................................116FIGURE 61CASSINI TARANGE COMPRESSEDPULSE #65016572........................................117FIGURE 62EXAMPLE OF FITTING IMPULSE SPREADER.........................................................117FIGURE 63CASSINI T3RANGE COMPRESSEDPULSE #65016573........................................118 FIGURE 64CASSINI T3RANGE COMPRESSEDPULSE #65026924........................................118 FIGURE 65MLEBEST FITTING PROCESS:ERROR DIVERGENCE. ..........................................119FIGURE 66SIMULATION OFAVERAGEDRANGE COMPRESSEDPULSE..................................119FIGURE 67THE RESULTS INMLEDIVERGENCE BECOMES AN ERROR IN TOPOGRAPHY

    ESTIMATION AS CLEARLY SHOWN..................................................................................120

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    Radar Altimeter General Waveform Model and Its Application to Cassini Mission 7

    ABSTRACT

    Since the first dedicated altimeter was launched on Seasat platform

    in 1978, the technology for conventional (pulse limited) radar altimeters has

    reached a certain