synthetic aperture radar for ionospheric scintillation … · 3/1/2018 isr seminar series...

Synthetic Aperture Radar for Ionospheric Scintillation Studies

Shradha Mohanty CSRE, IIT Bombay

Visiting Student, ISR, Boston College3/1/2018 ISR SEMINAR SERIES 2017-2018, BOSTON COLLEGE 1

Overview:

• Ionospheric scintillations• Synthetic Aperture Radar (SAR)

• How it works ?• How ionosphere affects SAR ?• What are the effects ?• What has been done so far ?

• SAR for scintillation identification• Effect of anisotropy on scintillation observed by SAR• Conclusion• Future Work

3/1/2018 ISR SEMINAR SERIES 2017-2018, BOSTON COLLEGE 2


Ionospheric effects on radio waves:

• Interaction of ionosphere with radio waves alters the wave properties

• Phase advance, group delay, Faraday rotation• Short-duration, high-intensity ionospheric

scintillations

• High priority due to its significant impact on satellite radio communication

• Also observed in low-frequency (L- and P-bands) synthetic aperture radar (SAR) signals

• Launch of several low-frequency spaceborne SAR missions, now and in future, has increased the enormity of the problem

wdc.nict.go.jp


Ionospheric Scintillations:

Cloud of Electrons

• Affects the amplitude and phase of signal

• Sources: Radio/ Beacon networks, Global Positioning System (GPS) and Synthetic Aperture Radar (SAR)


SAR – An Introduction:

www.radartutorials.euwww.radartutorials.eu



• Scattering Matrix [S]• Complex amplitude relating the incident and

scattered field• Elements are complex and depends upon

frequency, target orientation and shape, relative orientation of the polarization planes

• In the case of monostatic radar, reciprocity assumption (SHV = SVH) holds true

Scattering Matrix

www.laser-portal.ru



• Coherency [T] or Covariance [C] Matrix• Second order statistical parameters [C] and [T] • Generated from target vectors, Ω and K, respectively

www.doncio.navy.mil

Effects on GPS and SAR:

Rufenach, 1975



Effects on SAR:

• Defocusing ALOS2012706991ALOS2023056991


Effects on SAR:

Fringes due to Earthquake

Fringes due to Ionospheric effects

Fringes due to Earthquake persisting

Fringes due to ionosphere removed

Curtesy: Gomba, G., Cong, X.Y., Eineder, M., 2015

• Phase Instability


Effects on SAR:

• Azimuthal Streaking

ALPSRP256737070 ALPSRP276867070


Ionospheric Studies using SAR:

• Interferometric SAR (Phase)• Range Split-Spectrum

• Range Group – Phase Delay

• Azimuth shift• Multiple Aperture Interferometry

H.S. Jung et al., 2013.

𝑑𝑑𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 =−𝐾𝐾.𝑇𝑇𝑇𝑇𝑇𝑇

𝑓𝑓2 𝑑𝑑𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑝𝑝 =𝐾𝐾.𝑇𝑇𝑇𝑇𝑇𝑇𝑓𝑓2

Brcic et al., 2010.

∆∅𝑖𝑖𝑔𝑔𝑖𝑖𝑔𝑔 =𝑓𝑓𝐿𝐿𝑓𝑓𝐻𝐻

𝑓𝑓𝑔𝑔 𝑓𝑓𝐻𝐻2 − 𝑓𝑓𝐿𝐿2(∆∅𝐿𝐿𝑓𝑓𝐻𝐻 − ∆∅𝐻𝐻𝑓𝑓𝐿𝐿)

Rosen et al., 2010.


Ionospheric Studies using SAR:

• Polarimetric SAR (Intensity)• Scattering Matrix • Sub-banding• Image Contrast• Radar Cross-section Enhancement• Point Spread Function of Corner Reflector• Image Clutter Statistics

Faraday Rotation, TEC, Ionospheric altitude and drift velocity

S4, CKL, p


S4 measurements from SAR: (Belcher and Cannon,2014)

• Image Contrast (cd)

𝑐𝑐𝑑𝑑2 ≅4𝑆𝑆42

𝑁𝑁

𝑁𝑁 =𝐿𝐿𝑆𝑆𝑆𝑆

𝛾𝛾 𝜆𝜆𝑧𝑧𝑅𝑅 sec 𝜃𝜃

where, cd = 𝑝𝑝𝑠𝑠𝑔𝑔𝑝𝑝𝑔𝑔𝑝𝑝 𝑔𝑔𝑜𝑜 𝑖𝑖𝑖𝑖𝑖𝑖𝑝𝑝𝑖𝑖𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖 𝑝𝑝𝑖𝑖𝑑𝑑.𝑚𝑚𝑝𝑝𝑝𝑝𝑖𝑖 𝑖𝑖𝑖𝑖𝑖𝑖𝑝𝑝𝑖𝑖𝑝𝑝𝑖𝑖𝑖𝑖𝑖𝑖

where, N = independent Fresnel zone samplesγ = anisotropy ratiozr secθ = reduced slant range

• RCS Enhancement

𝜇𝜇𝑖𝑖𝑔𝑔𝑖𝑖𝑔𝑔 = 𝜇𝜇 (1 + 𝑆𝑆42)


CkL measurements from SAR:

(Belcher and Rogers, 2008Mannix et al., 2017)

• Point Spread Function (PSF) of Corner Reflector

𝑃𝑃𝑆𝑆𝑃𝑃𝜙𝜙 𝑘𝑘 = 𝑇𝑇𝑆𝑆𝐿𝐿𝑆𝑆( 𝑟𝑟𝑔𝑔2 + 𝑟𝑟2)−𝑝𝑝

𝑇𝑇𝑆𝑆𝐿𝐿𝑆𝑆 = 4𝛾𝛾𝑘𝑘𝑐𝑐1−𝑝𝑝𝐺𝐺𝑇𝑇𝑘𝑘𝐿𝐿 sec𝜃𝜃 (𝑟𝑟𝑝𝑝𝜆𝜆)2

𝜋𝜋Γ(𝑝𝑝2)

2𝜋𝜋 2Γ(𝑝𝑝 + 12 )

𝑘𝑘1𝑘𝑘𝑚𝑚𝑝𝑝+1


CkL measurements from SAR:

(Belcher et al., 2017)• From SAR image Clutter

𝜈𝜈𝑖𝑖𝑔𝑔𝑖𝑖𝑔𝑔 = 𝜈𝜈(1 +𝜎𝜎𝑆𝑆𝐿𝐿𝑆𝑆2

𝑙𝑙𝑔𝑔)

𝜎𝜎𝑆𝑆𝐿𝐿𝑆𝑆2 = 8𝜋𝜋𝛾𝛾2−𝑝𝑝𝐺𝐺 sec𝜃𝜃 (𝑟𝑟𝑝𝑝𝜆𝜆)2𝑐𝑐𝑝𝑝

𝑝𝑝 − 110−6𝐿𝐿𝑘𝑘𝑚𝑚

𝑝𝑝−1𝑇𝑇𝑘𝑘𝐿𝐿

𝑝𝑝 𝐼𝐼 =2 𝜈𝜈𝜇𝜇Γ 𝜐𝜐

𝜈𝜈𝜇𝜇𝐼𝐼

𝜈𝜈−1

𝐾𝐾𝜈𝜈−1(2𝜈𝜈𝜇𝜇𝐼𝐼)


ALOS-2/PALSAR-2 Specifications:

Satellite/Sensor ALOS-2 / PALSAR-2

Frequency of Operation 1.27 GHz

Bandwidth 28 MHz

Revisit, No. of cycles/day 14 days, 15

Mode of acquisition Full (Quad.) Polarimetry [HH+HV+VH+VV]

Width x Length (30 -55) km x 70 km

Resolution (Range x Azimuth) 3 - 10 m

Data Level 1.1 Single Look Complex

Orbit, Look direction Sun-synchronous, Right-/Left-looking

Height, inclination 698 km, 97.9°Time of acquisition (LT) 00:00 ± 15 min (asc.) , 12:00 ± 15 min (des.)

http://www.eorc.jaxa.jp/ALOS-2/en/about/palsar2.htm

1800 km

N23 Mar 2015 31 Oct 2016

B B


Scintillation Identification:

1800 km

N23 Mar 2015 31 Oct 2016

B B



1800 km

N23 Mar 2015 31 Oct 2016



B B

CALCUTTA


Scintillation Observations: GPS

RAJKOT CALCUTTA

TIRUNELVELI

TIRUNELVELI

RAJKOT


Scintillation Observations: GPS

RAJKOT CALCUTTA

TIRUNELVELI

TIRUNELVELI


Tirunelveli:Avg. S4 = 0.1 Avg. CkL = 1.45 x 1034

Rajkot:Avg. S4 = 0.15Avg. CkL = 1.72 x 1033


Avg. S4 from SAR = 0.19Avg. S4 from GPS at TIR = 0.10Avg. S4 from GPS at RAJ = 0.15

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 centre6.35⁰N, 150.90⁰E


Radar Cross-section Comparison:

Mag. Coord. of ROI centre12.84⁰N, 149.98⁰E

Boa Vista

Santarem

Alta Foresta

SAR Scene


Effect of Anisotropy:19 November 2010 6 April 2011

Scene Centre5.94° S, 65.13° WToA ~ 0300 UT

B B


Scintillation and Ionospheric Parameters from SAR

• Avg. S4, RCS Enhancement: 0.13• Avg. CkL : 1.68 x 1034 , log10(CkL) = 34.23 Axial

RatioOne-way S4 Log10(CkL)

10:1 0.1589 34.328320:1 0.1459 34.253230:1 0.143 34.235640:1 0.142 34.228950:1 0.1415 34.226460:1 0.1412 34.224570:1 0.141 34.222880:1 0.141 34.222890:1 0.141 34.2228

100:1 0.141 34.2228

• Avg. S4,Contrast : 0.14• Avg. CkL : 1.68 x 1034 , log10(CkL) = 34.23)

𝑇𝑇𝑑𝑑2 ≅4𝑆𝑆42

𝑁𝑁𝑁𝑁 =

𝐿𝐿𝑆𝑆𝑆𝑆𝜸𝜸 𝜆𝜆𝑧𝑧𝑅𝑅 sec 𝜃𝜃


15.129°N, 77.18°E

ToA~1900 UT

23 March 2015 31 October 2016


Scintillation and Ionospheric Parameters from SAR

• Avg. S4, RCS Enhancement: 0.154• Avg. CkL : 1.72 x 1034 , log10(CkL) = 34.27 Axial

RatioOne-way S4 Log10(CkL)

10:1 0.2443 34.65520:1 0.1863 34.418730:1 0.1664 34.31440:1 0.1573 34.264850:1 0.1524 34.236960:1 0.1496 34.220770:1 0.1478 34.2180:1 0.1466 34.20290:1 0.1458 34.198

100:1 0.1452 34.194

• Avg. S4,Contrast : 0.15• Avg. CkL : 1.66 x 1034 , log10(CkL) = 34.22)

𝑇𝑇𝑑𝑑2 ≅4𝑆𝑆42

𝑁𝑁𝑁𝑁 =

𝐿𝐿𝑆𝑆𝑆𝑆𝛾𝛾 𝜆𝜆𝑧𝑧𝑅𝑅 sec 𝜃𝜃


17 March 2015 26 April 2016

N N

52.16N, 172.46WToA ~ 2350 UT


A:B N S410:1 57.26 0.275110:2 45.607 0.245510:3 36.075 0.218410:4 29.34 0.196910:5 24.6 0.180310:6 21.17 0.167310:7 18.617 0.156910:8 16.655 0.148410:9 15.114 0.1413

10:10 13.88 0.1355

A:B N S410:1 57.26 0.275110:2 37.94 0.223910:3 27.29 0.189910:4 21.091 0.16710:5 17.127 0.150510:6 14.397 0.137910:7 12.412 0.128110:8 10.907 0.120110:9 9.7287 0.1134

10:10 8.782 0.1077

A:B N S410:1 57.26 0.275110:2 33.07 0.209110:3 22.97 0.174210:4 17.68 0.152910:5 14.49 0.138710:6 12.36 0.127810:7 10.876 0.1210:8 9.784 0.113710:9 8.955 0.1088

10:10 8.31 0.1048

A:B N S410:1 57.26 0.275110:2 30.534 0.210:3 21.193 0.167410:4 16.613 0.148210:5 13.968 0.135910:6 12.287 0.127410:7 11.149 0.121410:8 10.34 0.116910:9 9.75 0.1135

10:10 9.302 0.1109

A:B N S410:1 57.26 0.275110:2 29.775 0.198410:3 20.989 0.166610:4 16.859 0.149310:5 14.554 0.138710:6 13.13 0.131710:7 12.196 0.12710:8 11.548 0.123510:9 11.081 0.121

10:10 10.734 0.1191

A:B N S410:1 57.26 0.275110:2 30.5 0.200810:3 21.976 0.170410:4 18.038 0.154410:5 15.883 0.144910:6 14.577 0.138810:7 13.73 0.134710:8 13.15 0.131810:9 12.737 0.1298

10:10 12.434 0.1282

A:B N S410:1 57.26 0.275110:2 32.713 0.207910:3 24.16 0.178710:4 20.16 0.163210:5 17.978 0.154210:6 16.66 0.148410:7 15.812 0.144610:8 15.234 0.141910:9 14.823 0.14

10:10 14.522 0.1385

δ = 60° δ = 75° δ = 90° δ = 105°

δ = 120° δ = 135° δ = 150°

N


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 • Effect of anisotropy, and variation of axial ratio in particular, on the estimation

of scintillation and ionospheric parameters is discussed


On-going and Future Work:

• Extending the effect anisotropy on SAR data to mid- and high- latitudes

• Partial focusing of SAR data at ionospheric phase screen height to calculate ionospheric parameters and their comparison with those calculated from raw GPS data

Thank you


synthetic aperture radar for ionospheric scintillation … · 3/1/2018 isr seminar series...

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