Correction of Ionospheric Distortions in Low Frequency Interferometric SAR Data Jun Su Kim, Pau Prats & Konstantinos P. Pa...
SAR imaging through the Earth’s ionosphere <ul><li>Displacement (due to group delay) </li></ul><ul><li>Defocusing (dispers...
Azimuth shift decorrelation <ul><li>Determination of azimuth shift </li></ul>TEC change rate of 5 TECU/100 km Varying iono...
Azimuth shift: result (   comparison) Before After ALOS-PalSAR: Collville, Alaska <ul><li> -histogram </li></ul>Shift F...
Interferometric phase: First order effect <ul><li>Determination of interferometric phase     </li></ul><ul><li>Sensitiv...
Interferometric phase: correction and results - = Original  FR Corrected phase
Combined estimation: principle Mean -> FR  Slant -> shift Varying ionosphere <ul><li>Divide Ionosphere into N segments </l...
Combined estimation: estimation (phase and coherence) <ul><li>Equation to be solved </li></ul><ul><li>Solution: </li></ul>...
Correction using estimated   TEC <ul><li>Adoption of air-borne motion compensation </li></ul><ul><li>Flow chart </li></ul...
Full band vs. Sub-band az. shift estimation Low Middle High Full Low Middle High
Sub-band Correction scheme 6 sublooks 3 sublooks Full band
Differential az. sub-band interferogram GROUND ORBIT Ionospheric intensity S 1 S 2 S 3
Differential az. sub-band interferogram N=2 <ul><li>The more sub-bands (N) we have, (when coherence is good) </li></ul><ul...
Simulated 6MHz P-band data Without Ionospheric disturbances Coherence-range HH channel SLC Coherence with undisturbed mast...
Interferometric phase retrieval  (kp=3, Ckl=50) Ionospheric phase screen Coherence as a function of range Nr of Looks =3 A...
Interferometric phase retrieval (Far Range) Ionospheric phase screen Nr of Looks =3 A = 3,000 m Nr of Looks =33 A = 300 m ...
Conclusion Air-borne motion compensation method can be applied. Combination of Az shift and   FR gives better   TEC esti...
Correction of Ionospheric Distortions in Low Frequency Interferometric SAR Data Jun Su Kim, Pau Prats & Konstantinos P. Pa...
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Correction of ionospheric distortions in low frequency interferometric SAR data_final.ppt

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Correction of ionospheric distortions in low frequency interferometric SAR data_final.ppt

  1. 1. Correction of Ionospheric Distortions in Low Frequency Interferometric SAR Data Jun Su Kim, Pau Prats & Konstantinos P. Papathanassiou Microwave and Radar Institute German Aerospace Center
  2. 2. SAR imaging through the Earth’s ionosphere <ul><li>Displacement (due to group delay) </li></ul><ul><li>Defocusing (dispersion) </li></ul><ul><li>Small </li></ul><ul><li>Proportional to TEC (  TEC) itself </li></ul><ul><li>Azimuth distortions </li></ul><ul><li>Range distortions </li></ul><ul><li>Displacement (due to phase adv.) </li></ul><ul><li>Defocusing (ionosphere variation) </li></ul><ul><li>Large and visible </li></ul><ul><li>Proportional to derivative of dTEC/dx (d  TEC/dx) for displacement </li></ul>
  3. 3. Azimuth shift decorrelation <ul><li>Determination of azimuth shift </li></ul>TEC change rate of 5 TECU/100 km Varying ionosphere : Azimuth shift [pixel] : Velocity of piercing point : Pulse repetition frequency : Doppler rate : azimuth distance Satellite orbit
  4. 4. Azimuth shift: result (  comparison) Before After ALOS-PalSAR: Collville, Alaska <ul><li> -histogram </li></ul>Shift FR Contour: Impovement larger than 0.2 <ul><li>Best case (low  temp , weak  TEC var.) </li></ul>Pauli
  5. 5. Interferometric phase: First order effect <ul><li>Determination of interferometric phase    </li></ul><ul><li>Sensitivity </li></ul><ul><li>L-band: 13.30 rad./TECU= 2.12 cycle/TECU </li></ul><ul><li>1 cycle ~ 0.47 TECU </li></ul><ul><li>P-band: 38.82 rad./TECU= 6.18 cycle/TECU 1 cycle ~ 0.16 TECU </li></ul>Interferograms under ionospheric phases Collville Beaver
  6. 6. Interferometric phase: correction and results - = Original  FR Corrected phase
  7. 7. Combined estimation: principle Mean -> FR Slant -> shift Varying ionosphere <ul><li>Divide Ionosphere into N segments </li></ul>Coherent length = L <ul><li>Measure of FR </li></ul><ul><li>Measure of Azimuth shift </li></ul>Satellite orbit
  8. 8. Combined estimation: estimation (phase and coherence) <ul><li>Equation to be solved </li></ul><ul><li>Solution: </li></ul>FR only Combined Interferometric phase correction Coherence comparison:  a by 3-ways
  9. 9. Correction using estimated  TEC <ul><li>Adoption of air-borne motion compensation </li></ul><ul><li>Flow chart </li></ul>SLC Decompress  iono Compress SLC’ r iono =0 km r iono =100 km r iono =200 km r iono =300 km
  10. 10. Full band vs. Sub-band az. shift estimation Low Middle High Full Low Middle High
  11. 11. Sub-band Correction scheme 6 sublooks 3 sublooks Full band
  12. 12. Differential az. sub-band interferogram GROUND ORBIT Ionospheric intensity S 1 S 2 S 3
  13. 13. Differential az. sub-band interferogram N=2 <ul><li>The more sub-bands (N) we have, (when coherence is good) </li></ul><ul><li>the finer structure we get, </li></ul><ul><li>we can avoid phase unwrapping , </li></ul><ul><li>the higher resistance to the decorrelation it has. </li></ul>N=9  a estimation
  14. 14. Simulated 6MHz P-band data Without Ionospheric disturbances Coherence-range HH channel SLC Coherence with undisturbed master (N=81) Under Ionospheric disturbances (kp=3, Ckl=50)
  15. 15. Interferometric phase retrieval (kp=3, Ckl=50) Ionospheric phase screen Coherence as a function of range Nr of Looks =3 A = 3,000 m Nr of Looks =33 A = 300 m Nr of Looks =10 A = 1,000 m Nr of Looks =100 A = 100 m
  16. 16. Interferometric phase retrieval (Far Range) Ionospheric phase screen Nr of Looks =3 A = 3,000 m Nr of Looks =33 A = 300 m Nr of Looks =10 A = 1,000 m Nr of Looks =100 A = 100 m
  17. 17. Conclusion Air-borne motion compensation method can be applied. Combination of Az shift and  FR gives better  TEC estimation. Azimuth shift can be corrected for slow ionospheric variations. Azimuth full band approach Performance increases with increasing number of looks (i.e. degreasing azimuth apperture) on the cost of spatial resolution. Sub-band inter-interferogram is well coincidence with direct shift estimation Azimuth shift is compensated also in sub-bands. Azimuth sub-band approach Sub-band approach always give finer structure of the ionosphere
  18. 18. Correction of Ionospheric Distortions in Low Frequency Interferometric SAR Data Jun Su Kim, Pau Prats & Konstantinos P. Papathanassiou Microwave and Radar Institute German Aerospace Center

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