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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



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


Effects on GPS and SAR:


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)


Case Study

2000 km

N23-Mar-2015 31-Oct-2016

B B


Case Study

CALCUTTA


Scintillation Observations: GPS

RAJKOT CALCUTTA

TIRUNELVELI

TIRUNELVELI

RAJKOT


Scintillation Observations: GPS

RAJKOT CALCUTTA

TIRUNELVELI

TIRUNELVELI


One-way S4Vertically

integrated Strength of Turbulence

Propagation angle

Reduced slant propagation distance

Spectral slopeGeometry and

propagation factor


Avg. CkL at Tirunelveli1.45 x 1034

Avg. CkL at Rajkot 1.72 x 1033


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)


Scintillation Observations: SAR

•S4 measurements:• Image Contrast (Cd) •RCS Enhancement

SAR for Scintillation Identification:

• Motivation• Image pairs with uniform background• Satellite’s viewing geometry details• Need for simple identification options


• Coefficient of variance (CoV)• Local homogeneity/heterogeneity• Speckle filtering

HH

VV

HV

VH


CoV of SAR Intensities at different polarizations


CoV of other SAR quantities

TOTAL POWER VOLUME POWER


Radar Cross-section Comparison:

Mag. Coord. of ROI centre

6.35⁰N, 150.90⁰E




6.35⁰N, 150.90⁰E




12.84⁰N, 149.98⁰E


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


Acknowledgement: Prof. Charles Carrano, ISR, Boston College

Data: JAXA’s RA6 Project No. 3169 and RA4 Project No. 1396

Shradha [email protected]

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