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Full Polarimetric Synthetic Aperture Radar (SAR) Data for Ionosphere Observation - A Comparative
Study
Shradha Mohanty1*, Gulab Singh1
1CSRE, IIT Bombay
*Visiting Researcher at ISR, Boston College
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 1
Overview:
• Ionospheric Scintillation• Effects on satellites• Observation: GPS • Measurements: SAR as a proxy
• SAR for scintillation identification• Indices
• SAR RCS Comparison
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 2
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 3
Scintillation:
• Interaction of ionosphere with radio waves alters the wave properties• Background electrons
• Short-duration, high-intensity Ionospheric Scintillations
• High priority due to its significant impact on satellite radio, GPS communication, etc.
• Observed in low-frequency (L- and P-bands) SAR signals
Cloud of Electrons
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 4
Effects on GPS and SAR:
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 5
Effects on GPS and SAR:
•Defocusing
• Inaccurate phase calculation
•Azimuthal streaking
•RCS instability
Rufenach, 1975
Satellite/Sensor ALOS-2 / PALSAR-2
Frequency of Operation
1.27 GHz
Bandwidth 28 MHz
Revisit, No. of cycles/day
14 days, 15
Mode Full Pol [HH+HV+VH+VV]
Width x Length 30 km x 70 km
Resolution 10 m (8.7 m x 5.3 m)
Data Level 1.1 Single Look Complex
Orbit Sun-synchronous, Right-looking
Height, inclination 698 km, 97.9°
Date 23-Mar-2015, 31-Oct-2016
Time 18:54 – 18:59 hrs (UTC)
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 6
Case Study
2000 km
N23-Mar-2015 31-Oct-2016
B B
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 7
Case Study
2000 km
N23-Mar-2015 31-Oct-2016
B B
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 8
Case Study
2000 km
N23-Mar-2015 31-Oct-2016
B B
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 9
Case Study
CALCUTTA
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Scintillation Observations: GPS
RAJKOT CALCUTTA
TIRUNELVELI
TIRUNELVELI
RAJKOT
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 11
Scintillation Observations: GPS
RAJKOT CALCUTTA
TIRUNELVELI
TIRUNELVELI
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 12
One-way S4Vertically
integrated Strength of Turbulence
Propagation angle
Reduced slant propagation distance
Spectral slopeGeometry and
propagation factor
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 13
Avg. CkL at Tirunelveli1.45 x 1034
Avg. CkL at Rajkot 1.72 x 1033
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 14
Scintillation Observations: SAR
•S4 measurements:• Image Contrast (Cd) •RCS Enhancement
(Belcher and Cannon, 2014)
•CkL measurements:
•Side Lobe Function (SLF) of Corner Reflector
• Image Clutter
(Mannix et al., 2017)
(Belcher et al., 2017)
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Scintillation Observations: SAR
•S4 measurements:• Image Contrast (Cd) •RCS Enhancement
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 16
SAR for Scintillation Identification:
• Motivation• Image pairs with uniform background• Satellite’s viewing geometry details• Need for simple identification options
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• Coefficient of variance (CoV)• Local homogeneity/heterogeneity• Speckle filtering
HH
VV
HV
VH
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CoV of SAR Intensities at different polarizations
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CoV of other SAR quantities
TOTAL POWER VOLUME POWER
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Radar Cross-section Comparison:
Mag. Coord. of ROI centre
6.35⁰N, 150.90⁰E
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 22
Radar Cross-section Comparison:
Mag. Coord. of ROI centre
6.35⁰N, 150.90⁰E
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Radar Cross-section Comparison:
Mag. Coord. of ROI centre
12.84⁰N, 149.98⁰E
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 24
Radar Cross-section Comparison:
Mag. Coord. of ROI centre
12.84⁰N, 149.98⁰E
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 25
Conclusion:
• SAR can be helpful in augmenting and complementing GPS in scintillation studies
• Demerit: SAR image pair with unchanged background• Need: simple identification techniques
• Coeff. of Variation of Intensity is not a good measure• Introduction of Total Power and Depolarized Power measures
• Varying response of SAR RCS to scintillation may be explained by many factors
Thanks for your attention
12/11/2017 AGU FALL MEETING | 11 - 15 DECEMBER 2017 | NEW ORLEANS 26
Acknowledgement: Prof. Charles Carrano, ISR, Boston College
Data: JAXA’s RA6 Project No. 3169 and RA4 Project No. 1396
Shradha [email protected]