 | Brautigam B. Instrument calibration of spaceborne SAR systems: Diss. … Dr-Ing. / Deutsches Zentrum für Luft- und Raumfahrt, Institut für Hochfrequenztechnik und Radarsysteme, Oberpfaffenhofen. - Köln: DLR, 2014. - xx, 194 p.: ill. - (Forschungsbericht; 2014-41). - Bibliogr.: p.180-193. - ISSN 1434-8454
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Zusammenfassung ................................................. v
Abstract ...................................................... vii
Acronyms and Symbols ........................................... ix
1 Introduction ................................................. 1
1.1 Motivation for SAR Calibration .......................... 2
1.2 Goals of the Thesis ..................................... 3
1.3 Chapter Overview ........................................ 5
2 SAR Image Formation .......................................... 8
2.1 Radar Fundamentals ...................................... 8
2.2 SAR Principle .......................................... 12
2.2.1 Azimuth Signal Theory ........................... 14
2.2.2 Range Signal Theory ............................. 16
2.3 Matched Filtering of SAR Data .......................... 18
2.4 SAR Imaging Modes ...................................... 22
3 Calibration of Spaceborne SAR Systems ....................... 25
3.1 SAR Instrument Model ................................... 26
3.1.1 Error Types ..................................... 26
3.1.2 Error Contributions to the SAR System ........... 28
3.1.3 Instrument Power-Gain Value ..................... 30
3.2 SAR Calibration Concepts ............................... 32
3.2.1 Evolution of Spaceborne SAR Instrument
Calibration ..................................... 33
3.2.2 An Innovative System Calibration Concept ........ 35
4 Instrument Impacts and Error Sources ........................ 40
4.1 SAR Instrument Setup ................................... 40
4.1.1 Digital Unit .................................... 42
4.1.2 RF Unit ......................................... 43
4.1.3 Active Antenna Front-End ........................ 43
4.2 Internal Error Sources ................................. 45
4.2.1 Front-End Error Sources ......................... 46
4.2.2 Signal Demodulation ............................. 48
4.2.3 Quantization .................................... 49
4.2.4 Internal Delay .................................. 50
4.2.5 Noise ........................................... 52
4.3 Instrument Effects on Gain and Phase ................... 52
4.3.1 Instrument Model ................................ 52
4.3.2 Short-Term and Long-Term Variations ............. 54
4.4 Active Phased Array Antenna ............................ 55
4.4.1 Radiation Characteristics ....................... 56
4.4.2 Antenna Degradation ............................. 59
4.5 Summary of SAR Signal Error Impacts .................... 60
5 Internal Calibration - Design, Algorithms and Simulation .... 64
5.1 Internal Calibration Hardware in Spaceborne SAR
Sensors ................................................ 64
5.1.1 General Approach ................................ 64
5.1.2 Calibration Signals ............................. 66
5.1.3 On-Ground Characterization ...................... 70
5.2 Strategy for Internal Calibration Acquisition .......... 74
5.2.1 Assumptions for Calibration Pulse Commanding .... 74
5.2.2 Missing SAR Echoes due to Calibration ........... 75
5.2.3 Sequence for Instrument Drift Measurement ....... 78
5.2.4 Sequences for Front-End Temperature
Compensation .................................... 82
5.2.5 Sequence for Robust Replica Retrieval ........... 83
5.3 Internal Calibration Algorithms ........................ 87
5.3.1 ADC Correction .................................. 88
5.3.2 I/Q Channels Correction ......................... 89
5.3.3 Compensation of Fast-Time Instrument
Variations ...................................... 91
5.3.4 Replica Generation .............................. 92
5.3.5 Range Compression and Gain Normalization ........ 98
5.3.6 Phase Delay and Channel Balancing for
Polarimetrie and Multi-Phase Center Systems ..... 99
5.3.7 Correction of Calibration Network
Dependencies ................................... 101
5.3.8 Instrument Drift Compensation .................. 102
5.3.9 Quality Analysis ............................... 103
5.4 Active Phased Array Antenna - Performance Control ..... 106
5.4.1 Novel Performance Control using
a Mathematical Antenna Model and TRM Phase
Coding ......................................... 106
5.4.2 Reconstruction Algorithm ....................... 107
5.4.3 Error Analysis of Applicable Codes ............. 111
5.4.4 Advanced Failure Detection Method .............. 114
5.4.5 Dynamic Range Reduction Algorithm .............. 117
5.4.6 Antenna Performance Update ..................... 118
5.5 Summary of the Instrument Calibration Concept ......... 120
6 Results from Spaceborne Instrument Measurements with
TerraSAR-X ................................................. 122
6.1 The TerraSAR-X System ................................. 122
6.1.1 Mission Overview ............................... 122
6.1.2 SAR Payload .................................... 125
6.1.3 Instrument Units ............................... 127
6.1.4 Internal Calibration Sub-System ................ 128
6.1.5 System Calibration of TerraSAR-X ............... 128
6.2 Instrument In-Orbit Characterization .................. 130
6.2.1 I/Q Characteristics ............................ 130
6.2.2 Attenuator Offsets ............................. 132
6.2.3 Calibration Network Stability .................. 135
6.3 Internal Calibration Results .......................... 139
6.3.1 SAR Image Quality Improvement .................. 139
6.3.2 Calibration Accuracy of Two Compensation
Strategies ..................................... 146
6.3.3 Balancing of the Experimental Dual Channel
System ......................................... 149
6.4 Antenna Performance Monitoring ........................ 151
6.4.1 On-Ground Verification of Estimation Method .... 151
6.4.2 In-Orbit TRM Monitoring Results ................ 155
6.4.3 Measurement Accuracy ........................... 157
6.5 Long-Term Instrument Variation ........................ 161
6.5.1 Temperature Behavior ........................... 161
6.5.2 Power and Gain Monitoring ...................... 162
6.5.3 TRM Long-Term Performance ...................... 164
6.6 Summary of TerraSAR-X Results ......................... 165
7 Conclusions ................................................ 167
7.1 Thesis Summary ........................................ 167
7.2 Lessons Learned and Outlook on Upcoming Challenges .... 170
A SAR System Model ........................................... 173
B Definition of Phased Array Antenna Coordinate System ....... 175
B.l Spherical Antenna Coordinate System ................... 175
B.2 Phased Array Numbering Convention ..................... 176
C Spectrogram Generation ..................................... 178
Bibliography .................................................. 180
Curriculum Vitae .............................................. 195
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