Synthetic Aperture Radar for Ionospheric Scintillation Studies

Transcription

1 Synthetic Aperture Radar for Ionospheric Scintillation Studies Shradha Mohanty CSRE, IIT Bombay Visiting Student, ISR, Boston College 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 1

2 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 , BOSTON COLLEGE 2

3 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 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 3

4 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) 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 4

5 SAR An Introduction: 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 5

6 SAR An Introduction: 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 (S HV = S VH ) holds true Scattering Matrix 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 6

7 SAR An Introduction: Coherency [T] or Covariance [C] Matrix Second order statistical parameters [C] and [T] Generated from target vectors, Ω and K, respectively 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 7

8 Effects on GPS and SAR: Rufenach, /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 8

9 Effects on SAR: Defocusing ALOS ALOS /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 9

10 Effects on SAR: Phase Instability Fringes due to Earthquake Fringes due to Earthquake persisting Fringes due to ionosphere removed Fringes due to Ionospheric effects Curtesy: Gomba, G., Cong, X.Y., Eineder, M., /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 10

11 Effects on SAR: ALPSRP ALPSRP Azimuthal Streaking 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 11

12 Ionospheric Studies using SAR: Interferometric SAR (Phase) Range Split-Spectrum iiiiiiii = ff LL ff HH ff oo ff HH 2 ff LL 2 ( LLff HH HH ff LL ) Range Group Phase Delay Rosen et al., dd ppppppppp = KK. TTTTTT ff 2 dd gggggggggg = KK. TTTTTT ff 2 Brcic et al., Azimuth shift Multiple Aperture Interferometry H.S. Jung et al., /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 12

13 Ionospheric Studies using SAR: Polarimetric SAR (Intensity) Scattering Matrix Faraday Rotation, TEC, Ionospheric altitude and drift velocity Sub-banding Image Contrast Radar Cross-section Enhancement S4, C Point Spread Function of Corner Reflector K L, p Image Clutter Statistics 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 13

14 S4 measurements from SAR: (Belcher and Cannon,2014) Image Contrast (c d ) cc dd 2 4SS 4 2 NN ssssssssssss oooo iiiiiiiiiiiiiiiiii ssssss. where, c d = mmmmmmmm iiiiiiiiiiiiiiiiii NN = γγ LL SSSS λλzz RR sec θθ where, N = independent Fresnel zone samples γ = anisotropy ratio z r secθ = reduced slant range RCS Enhancement μμ iiiiiiii = μμ (1 + SS 4 2 ) 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 14

15 CkL measurements from SAR: Point Spread Function (PSF) of Corner Reflector (Belcher and Rogers, 2008 Mannix et al., 2017) PPPPPP φφ kk = TT SSSSSS ( rr oo 2 + rr 2 ) pp TT SSSSSS = 4γγkk cc 1 pp GGCC kk LL sec θθ (rr ee λλ) 2 ππγ( pp 2 ) pp+1 2ππ 2 Γ( pp ) kk 1kkkk 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 15

16 CkL measurements from SAR: From SAR image Clutter pp II = 2 νν μμ Γ υυ νν μμ II (Belcher et al., 2017) νν 1 KK νν 1 (2 νν μμ II) νν iiiiiiii = νν(1 + σσ 2 SSSSSS ) ll rr 2 σσ SSSSSS = 8ππγγ 2 pp GG sec θθ (rr ee λλ) 2 cccc pp LL pp 1 kkkk CC kk LL 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 16

17 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.) 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 17

18 Scintillation Identification: 23 Mar Oct 2016 N 1800 km B B 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 18

19 Scintillation Identification: 23 Mar Oct 2016 N 1800 km B B 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 19

20 Scintillation Identification: 23 Mar Oct 2016 N 1800 km B B 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 20

21 Scintillation Observations: GPS CALCUTTA TIRUNELVELI RAJKOT CALCUTTA TIRUNELVELI 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 21

22 Scintillation Observations: GPS RAJKOT TIRUNELVELI RAJKOT CALCUTTA TIRUNELVELI 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 22

23 Tirunelveli: Avg. S4 = 0.1 Avg. CkL = 1.45 x Rajkot: Avg. S4 = 0.15 Avg. CkL = 1.72 x /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 23

24 Avg. S4 from SAR = 0.19 Avg. S4 from GPS at TIR = 0.10 Avg. S4 from GPS at RAJ = /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 24

25 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 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 25

26 CoV of SAR Intensities at different polarizations HH HV VV VH 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 26

27 CoV of other SAR quantities TOTAL POWER VOLUME POWER 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 27

28 Radar Cross-section Comparison: Mag. Coord. of ROI centre 6.35⁰N, ⁰E 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 28

29 Radar Cross-section Comparison: Mag. Coord. of ROI centre 12.84⁰N, ⁰E 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 29

30 Effect of Anisotropy: 19 November April 2011 B B Boa Vista Santarem SAR Scene Alta Foresta Scene Centre 5.94 S, W ToA ~ 0300 UT 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 30

31 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 31

32 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 32

33 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 33

34 Scintillation and Ionospheric Parameters from SAR Avg. S4, RCS Enhancement: 0.13 Avg. CkL : 1.68 x 10 34, log 10 (CkL) = Avg. S4,Contrast : 0.14 Avg. CkL : 1.68 x 10 34, log 10 (CkL) = 34.23) CC dd 2 4SS 4 2 NN NN = LL SSSS γγ λλzz RR sec θθ Axial One-way S4 Log 10 (CkL) Ratio 10: : : : : : : : : : /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 34

35 23 March October N, E ToA ~1900 UT 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 35

36 Scintillation and Ionospheric Parameters from SAR Avg. S4, RCS Enhancement: Avg. CkL : 1.72 x 10 34, log 10 (CkL) = Avg. S4,Contrast : 0.15 Avg. CkL : 1.66 x 10 34, log 10 (CkL) = 34.22) CC 2 dd 4SS 4 2 NN = NN γγ LL SSSS λλzz RR sec θθ Axial One-way S4 Log 10 (CkL) Ratio 10: : : : : : : : : : /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 36

37 17 March April 2016 N N 52.16N, W ToA ~ 2350 UT 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 37

38 δ = 60 δ = 75 δ = 90 δ = 105 A:B N S4 10: : : : : : : : : : A:B N S4 10: : : : : : : : : : A:B N S4 10: : : : : : : : : : δ = 120 δ = 135 δ = 150 A:B N S4 10: : : : : : : : : : A:B N S4 10: : : : : : : : : : A:B N S4 10: : : : : : : : : : A:B N S4 10: : : : : : : : : : /1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 38 N

39 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 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 39

40 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 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 40

41 Thank you 3/1/2018 ISR SEMINAR SERIES , BOSTON COLLEGE 41