Abstract ...................................................... iii
Zusammenfassung ................................................. v
Contents ....................................................... ix
1 Introduction ............................................... 1
1.1 Motivation ................................................. 1
1.2 Scope ...................................................... 2
1.3 Thesis structure ........................................... 2
2 Fundamentals and state of the art .......................... 5
2.1 Ionosphere ................................................. 5
2.1.1 Electron density temporal variations ................ 6
2.1.2 Electron density spatial variations ................. 6
2.1.3 Ionospheric effects on radio waves .................. 9
2.2 Ionospheric effects on SAR ................................ 13
2.2.1 Range delay and phase advance ...................... 13
2.2.2 Range impulse response ............................. 14
2.2.3 Azimuth impulse response ........................... 15
2.2.4 Faraday rotation ................................... 17
2.2.5 Amplitude scintillation ............................ 18
2.3 Ionospheric effects on InSAR .............................. 18
2.3.1 Range delay and phase advance ...................... 20
2.3.2 Azimuth shift ...................................... 21
2.4 Discussion ................................................ 22
2.5 Ionosphere correction methods ............................. 22
2.5.1 Absolute ionosphere ................................ 23
2.5.2 Differential ionosphere ............................ 23
2.6 Conclusion and organization of the thesis ................. 25
3 The split-spectrum method ................................. 27
3.1 The range split-spectrum method ........................... 27
3.1.1 Split-spectrum method accuracy .................... 28
3.2 Implementation and systematic errors ...................... 29
3.2.1 Multilooking ....................................... 29
3.2.2 Filtering .......................................... 30
3.2.3 Phase unwrapping errors ............................ 31
3.2.4 Asymmetrie split-spectrum mode ..................... 32
3.3 Application Examples ...................................... 32
3.3.1 2008 Kyrgyzstan earthquake ......................... 33
3.3.2 Aurora borealis .................................... 34
3.3.3 2008 Wenchuan earthquake ........................... 34
3.3.4 Asymmetric split-spectrum mode ..................... 38
3.4 Conclusion ................................................ 38
4 The split-spectrum method for TOPS and ScanSAR ............ 41
4.1 Ionospheric effects on squinted acquisitions imaging ...... 41
4.1.1 Azimuth shifts ..................................... 42
4.2 Ionospheric effects on squinted acquisitions processing ... 43
4.2.1 Azimuth shift estimation ........................... 43
4.2.2 Azimuth shift resampling ........................... 44
4.2.3 Interferogram ...................................... 44
4.3 Ionospheric phase screen compensation ..................... 45
4.3.1 Split-spectrum raw estimate ........................ 47
4.3.2 Ionospheric shift phase bias compensation .......... 48
4.3.3 Ionospheric phase screen compensation .............. 48
4.3.4 Burst overlap phase check .......................... 50
4.4 Full-aperture ScanSAR mode ................................ 50
4.4.1 Comparison with trend removal ...................... 51
4.5 Conclusion ................................................ 51
5 Semi-focusing processing and integrated azimuth shifts .... 55
5.1 Method .................................................... 55
5.2 Integrated azimuth shifts ................................. 57
5.3 Conclusion ................................................ 59
6 Improved estimation by data combination ................... 61
6.1 Bayesian data combination ................................. 61
6.1.1 Ionosphere model and a-priori information .......... 62
6.2 Split-spectrum method and azimuth shifts combination ...... 63
6.2.1 Forward problem .................................... 63
6.3 Application examples ...................................... 65
6.3.1 Alaska aurora test case ............................ 65
6.3.2 Amazon scintillation test case ..................... 66
6.4 Conclusion ................................................ 68
7 Validation ................................................ 71
7.1 Validation with GNSS measurements ......................... 71
7.1.1 Comparison with global TEC maps .................... 71
7.1.2 Comparison with local GPS measurements ............. 73
8 Conclusion ................................................ 75
Appendix A
Gomba G., Parizzi A., De Zan F., Eineder M., and Bamler R.
(2016). Toward Operational Compensation of Ionospheric
Effects in SAR Interferograms: The Split-Spectrum Method.
IEEE Transactions on Geoscience and Remote Sensing, 54(3):
1446-1461 ...................................................... 77
Appendix В
Gomba G., Rodriguez Gonzalez F., and De Zan E. (2017).
Ionospheric Phase Screen Compensation for the Sentinel-1
TOPS and ALOS-2 ScanSAR modes. IEEE Transactions on
Geoscience and Remote Sensing .................................. 95
Appendix С
Gomba G. and De Zan E. (2016, submitted). Bayesian Data
Combination for the Estimation of Ionospheric Effects in SAR
Interferograms. IEEE Transactions on Geoscience and Remote
Sensing ....................................................... 109
Appendix D
Gomba G., Eineder M., Parizzi A., and Bamler R. (2014).
High-resolution estimation of ionospheric phase screens
through semi-focusing processing. 2014 IEEE International
Geoscience and Remote Sensing Symposium (IGARSS) .............. 123
Appendix E
Gomba G. and De Zan E. (2015). Estimation of ionospheric
height variations during an aurora event using multiple
semi-focusing levels. 2015 IEEE International Geoscience and
Remote Sensing Symposium (IGARSS) ............................. 129
Bibliography .................................................. 135
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