RFI_in_PALSAR_data.pdf

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RFI_in_PALSAR_data.pdf

  1. 1. Characterization and Extent of Randomly-ChangingRadio Frequency Interference in ALOS PALSAR Data FJ Meyer1) 2), J Nicoll2), AP Doulgeris3) 1)Earth& Planetary Remote Sensing, University of Alaska Fairbanks 2)Alaska Satellite Facility (ASF) 3)University of Tromsø, Romssa Universitehta. N-9037 Tromsø, NorwayCollaborating Organizations:
  2. 2. Outline • Motivation • An Uncharacteristic RFI Source in the American Arctic • Screening AADN’s PALSAR Archive for RFI Issues • Development of a Modified Notch Filter Approach for Signal Correction • Performance of Notch Filter Algorithm • ConclusionsIGARSS’11, Vancouver F. Meyer et al. 2
  3. 3. Motivation • In American Arctic, polarimetric data regularly affected by signal artifacts causing huge variations of polarimetric signature (see examples below) • Initial survey showed: More than 80% of data over Barrow, AK affected • Source: High power RF interferenceIGARSS’11, Vancouver F. Meyer et al. 3
  4. 4. An Uncharacteristic RFI Source in the American Arctic • DEW line and North Warning System: – Array of long-range and short-range over-the-horizon surveillance and early warning defense system of US and Canada – Originally ~ 90 sites located along American Arctic Coast – Migrated to North Warning System in 1985 and reduced to ~50 Sites Short-range stations Long-range stationsIGARSS’11, Vancouver F. Meyer et al. 4
  5. 5. The Long Range Radar System FPS-117 • AN/FPS-117 Long Range Radar (Lockheed-Martin): – Pulsed phased array antenna system, with a PRF of up to 1500Hz – L-band frequency range of 1215-1400 MHz (PALSAR fc: 1270 MHz) – Low power, long range (up to 450km) – Randomly hopping among 18 channels in the 1215-1400 MHz band. Specifications frequency: 1215 - 1400 MHz pulse repetition frequency (PRF): 250 / 1100 Hz pulsewidth (PW): 100 / 800 µs peak power: 20 kW displayed range: bis 463 km Source: Lockheed-Martin beamwidth: β:3,4°, ε:2,7°IGARSS’11, Vancouver F. Meyer et al. 5
  6. 6. Examples of Interference Signatures PALSAR PLR21.5: Orbit: 17260; Frame: 1440• Range-frequency azimuth-time representation: HH VV 6
  7. 7. Examples of Interference Signatures PALSAR PLR21.5: Orbit: 17260; Frame: 1440 • Bandwidth and Power: – ~ 1 – 2.5 MHz bandwidth; fc changing on pulse-by-pulse basis HH VVIGARSS’11, Vancouver F. Meyer et al. 7
  8. 8. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440• Focused SAR image without notch-filtering HH HV VV VH 8
  9. 9. PALSAR Operational Notch Filter • Notch filtering during range compression: – Range FFT of block of 256 azimuth lines – Average spectrum along azimuth – Analyze gain for anomalies & apply notch filter if anomaly is detected – Then perform range and azimuth compression • Problem: – Due to the wide bandwidth and changing center frequency, anomalies difficult to detect by PALSAR notch filter →Especially in the cross-pol channels, PALSAR processor not able to provide sufficiently corrected dataIGARSS’11, Vancouver F. Meyer et al. 9
  10. 10. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440• Focused SAR image with PALSAR operational notch-filtering HH HV VV VH 10
  11. 11. A Simple RFI Screening Method • Per column of range compressed raw data, calculate coherence between odd and even samples:  f even f odd CLine    f even f even f odd f odd • This coherence is composed of SAR signal and RFI components CLine  CRFI  CSAR • CSAR is small and can either be ignored or identified in an averaging process • The plot to the right shows results where high coherence peaks correspond to RFI affected linesIGARSS’11, Vancouver F. Meyer et al. 11
  12. 12. RFI Affected ALOS PALSAR Frames in the AADN Archive Severe Intermediate Not affectedIGARSS’11, Vancouver F. Meyer et al. 12 12
  13. 13. RFI Affected ALOS PALSAR Frames in the AADN Archive Severe Intermediate Not affected Test Site AlaskaIGARSS’11, Vancouver F. Meyer et al. 13 13
  14. 14. RFI Affected ALOS PALSAR Frames in the AADN Archive North Warning System Severe Intermediate Not affected Test Site AlaskaIGARSS’11, Vancouver F. Meyer et al. 14 14
  15. 15. RFI Affected ALOS PALSAR Frames in the AADN Archive North Warning System Severe Intermediate Not affected Military Bases & Airport Radars Test Site AlaskaIGARSS’11, Vancouver F. Meyer et al. 15 15
  16. 16. Notch Filtering based on Azimuth Analysis Original Data • Signatures are high power, narrow in azimuth time, wide bandwidth → detection based on azimuth analysis proposed • Workflow: Azimuth Time – Range compression – Range FFT – Cut through azimuth-time range-frequency diagram along azimuth – Detection of interference by local outlier analysis along azimuth – Notch filtering by removal of detected outliers – Azimuth compression Range FrequencyIGARSS’11, Vancouver F. Meyer et al. 16
  17. 17. Notch Filtering based on Azimuth Analysis After Notch Filtering • Signatures are high power, narrow in azimuth time, wide bandwidth → detection based on azimuth analysis proposed • Workflow: – Range compression – Range FFT – Cut through azimuth-time range-frequency diagram along azimuth – Detection of interference by local outlier analysis along azimuth – Notch filtering by removal of detected outliers – Azimuth compressionIGARSS’11, Vancouver F. Meyer et al. 17
  18. 18. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440• Focused SAR image without notch-filtering HH HV VV VH 18
  19. 19. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440• Focused SAR image with azimuth analysis-based notch-filtering HH HV VV VH 19
  20. 20. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440 HV No filter appliedIGARSS’11, Vancouver F. Meyer et al. 20
  21. 21. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440 HV PALSAR Operational filterIGARSS’11, Vancouver F. Meyer et al. 21
  22. 22. Effects on SAR Imaging and Polarimetry PALSAR PLR21.5: Orbit: 17260; Frame: 1440 HV Azimuth analysis-based filterIGARSS’11, Vancouver F. Meyer et al. 22
  23. 23. Correction Results – Polarimetric Signature PALSAR PLR21.5: Orbit: 16837; Frame: 1440 Geographic Location Acquisition Date: March 23, 2009 RFI Source: Long Range Radar Station Pauli Decomposition Pauli Decomposition (LRRS) near Point Barrow, AK After Notch Filtering Before Notch FilteringIGARSS’11, Vancouver F. Meyer et al. 23
  24. 24. Correction Results – Polarimetric Signature PALSAR PLR21.5: Orbit: 17085; Frame: 1440 Geographic Location Acquisition Date: April 09, 2009 RFI Source: Long Range Radar Station Pauli Decomposition Pauli Decomposition (LRRS) near Point Barrow, AK After Notch Filtering Before Notch FilteringIGARSS’11, Vancouver F. Meyer et al. 24
  25. 25. Correction Results – Polarimetric Signature PALSAR PLR21.5: Orbit: 17260; Frame: 1440 Geographic Location Acquisition Date: April 21, 2009 RFI Source: Long Range Radar Station Pauli Decomposition Pauli Decomposition (LRRS) near Point Barrow, AK After Notch Filtering Before Notch FilteringIGARSS’11, Vancouver F. Meyer et al. 25
  26. 26. Benefit of Developed RFI Filter for Polarimetric Classification of Sea Ice Features Operationally Processed Data Custom RFI-Filtered DataIGARSS’11, Vancouver F. Meyer et al. 26
  27. 27. Benefit of Developed RFI Filter for Polarimetric Classification of Sea Ice Features After RFI Filtering → Quality of classification result visually improvedIGARSS’11, Vancouver F. Meyer et al. 27
  28. 28. RFI monitoring by JERS-1 SAR (1992-1998)Normalized zero padded bandwidth (%) 0 10.0
  29. 29. RFI monitoring by PALSAR (2010~2011)Normalized zero padded bandwidth (%) 0 10.0
  30. 30. Conclusions and Recommendations: • L-band interference from over-the-horizon radars problematic in large parts of the American Arctic • Pulsed ground based systems cause temporarily narrow, high-power, and wide bandwidth interferences with randomly changing fc • Standard PALSAR processing scheme insufficient for removing interferences • A modified azimuth-based filtering algorithm shows good performance in removing RFI signals and restoring original data quality • Real data examples show successful mitigation of interferences • Polarimetric signatures after RFI filtering significantly improved • Growing issues of RFI in Microwave Remote Sensing needs to be addressedIGARSS’11, Vancouver F. Meyer et al. 30 30
  31. 31. ANNOUNCEMENT: 2011 CEOS SAR Calibration and Validation Workshop Fairbanks, Alaska Workshop Dates: November 7 – 9, 2011 Abstract Deadline: September 14, 2011 More information at: www.asf.alaska.edu/ceos_workshop/IGARSS’11, Vancouver F. Meyer et al. 31 31
  32. 32. Open Three Year PhD Position starting fall 2011 / spring 2012 for a radar remote sensing research project at the Geophysical Institute of the University of Alaska Fairbanks on Theoretical Investigations into the Impact and Mitigation of Ionospheric Effects on Low-Frequency SAR and InSAR Data Research Focus: • Investigation of spatial and temporal properties of ionospheric effects in SAR data • Development of statistical signal models • Design of optimized methods for ionospheric correction More information: Dr. Franz Meyer (fmeyer@gi.alaska.edu) and at: www.insar.alaska.eduIGARSS’11, Vancouver F. Meyer et al. 32
  33. 33. Image and kml Creation • An average coherence is calculated per image. For example to the right C=0.010 (1.0% RFI coherence) • A kml bounding box is created and color coded according to interference severity (green=low RFI, yellow=moderate RFI, and red= high RFI).IGARSS’11, Vancouver F. Meyer et al. 33

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