TH1.L09 - INVESTIGATIONS ON TOPS INTERFEROMETRY WITH TERRASAR-X

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  • Concerning your questions: 1) if baseband az. Scaling is used for sliding spot and spot it is less effective than azimuth scaling + Specan, right? Baseband azimuth scaling is more efficient for sliding spotlight when using azimuth scaling+specan (1 FFT and one phase product less), but less efficient for spotlight with azimuth scaling+specan. Note than in the current TSX operational processor for sliding spotlight you need to make several steps for side-lobe supression (what Jesus did), while with the new approach you can do these within the matched filter. For normal spotlight you don't need these additional steps as the weighting is performed in time domain before azimuth compression. 2) What is the correct name of the Algorithm: ECS for TOPSAR? I would say something like ECS with baseband azimuth scaling. Although we developed the algorithm for TOPS, maybe it is good not to relate it to TOPS exclusively, as it can also be applied to other modes (indeed, it is more efficient for sliding spotlight than existing approaches, as commented in the previous point). In general, I think our solution can be interesting in any mode (existing or to be invented) where there is some azimuth steering of the antenna, or alternatively, where there is a Doppler centroid variation along azimuth within the data take.
  • Concerning your questions: 1) if baseband az. Scaling is used for sliding spot and spot it is less effective than azimuth scaling + Specan, right? Baseband azimuth scaling is more efficient for sliding spotlight when using azimuth scaling+specan (1 FFT and one phase product less), but less efficient for spotlight with azimuth scaling+specan. Note than in the current TSX operational processor for sliding spotlight you need to make several steps for side-lobe supression (what Jesus did), while with the new approach you can do these within the matched filter. For normal spotlight you don't need these additional steps as the weighting is performed in time domain before azimuth compression. 2) What is the correct name of the Algorithm: ECS for TOPSAR? I would say something like ECS with baseband azimuth scaling. Although we developed the algorithm for TOPS, maybe it is good not to relate it to TOPS exclusively, as it can also be applied to other modes (indeed, it is more efficient for sliding spotlight than existing approaches, as commented in the previous point). In general, I think our solution can be interesting in any mode (existing or to be invented) where there is some azimuth steering of the antenna, or alternatively, where there is a Doppler centroid variation along azimuth within the data take.
  • Concerning your questions: 1) if baseband az. Scaling is used for sliding spot and spot it is less effective than azimuth scaling + Specan, right? Baseband azimuth scaling is more efficient for sliding spotlight when using azimuth scaling+specan (1 FFT and one phase product less), but less efficient for spotlight with azimuth scaling+specan. Note than in the current TSX operational processor for sliding spotlight you need to make several steps for side-lobe supression (what Jesus did), while with the new approach you can do these within the matched filter. For normal spotlight you don't need these additional steps as the weighting is performed in time domain before azimuth compression. 2) What is the correct name of the Algorithm: ECS for TOPSAR? I would say something like ECS with baseband azimuth scaling. Although we developed the algorithm for TOPS, maybe it is good not to relate it to TOPS exclusively, as it can also be applied to other modes (indeed, it is more efficient for sliding spotlight than existing approaches, as commented in the previous point). In general, I think our solution can be interesting in any mode (existing or to be invented) where there is some azimuth steering of the antenna, or alternatively, where there is a Doppler centroid variation along azimuth within the data take.
  • Thank you for your attention!
  • Concerning your questions: 1) if baseband az. Scaling is used for sliding spot and spot it is less effective than azimuth scaling + Specan, right? Baseband azimuth scaling is more efficient for sliding spotlight when using azimuth scaling+specan (1 FFT and one phase product less), but less efficient for spotlight with azimuth scaling+specan. Note than in the current TSX operational processor for sliding spotlight you need to make several steps for side-lobe supression (what Jesus did), while with the new approach you can do these within the matched filter. For normal spotlight you don't need these additional steps as the weighting is performed in time domain before azimuth compression. 2) What is the correct name of the Algorithm: ECS for TOPSAR? I would say something like ECS with baseband azimuth scaling. Although we developed the algorithm for TOPS, maybe it is good not to relate it to TOPS exclusively, as it can also be applied to other modes (indeed, it is more efficient for sliding spotlight than existing approaches, as commented in the previous point). In general, I think our solution can be interesting in any mode (existing or to be invented) where there is some azimuth steering of the antenna, or alternatively, where there is a Doppler centroid variation along azimuth within the data take.
  • TH1.L09 - INVESTIGATIONS ON TOPS INTERFEROMETRY WITH TERRASAR-X

    1. 1. Investigations on TOPS Interferometry with TerraSAR-X Pau Prats , Luca Marotti, Steffen Wollstadt, Rolf Scheiber Microwaves and Radar Institute (HR) German Aerospace Center
    2. 2. <ul><li>TOPS is a wide-swath mode that achieves an azimuth-invariant DTAR and SNR, i.e., no scalloping. </li></ul><ul><li>The antenna is steered from backwards to forwards, so that every target on ground is observed under the same antenna pattern . </li></ul><ul><li>The TOPS mode will be the default mode for the IWS (250 km) and EWS (400 km) for the Sentinel-1 satellites. </li></ul><ul><li>The TOPS mode was first demonstrated in-orbit by TerraSAR-X . </li></ul>Terrain Observation by Progressive Scans (TOPS) F. De Zan and A. Monti Guarnieri , “TOPSAR: Terrain Observation by Progressive Scans,” IEEE Trans. On Geoscience and Remote Sensing , vol. 44, no. 9, Sept. 2006.
    3. 3. TOPS Time-Frequency Diagram P. Prats, R. Scheiber, J. Mittermayer, A. Meta and A. Moreira, “Processing of Sliding Spotlight and TOPS SAR Data Using Baseband Azimuth Scaling,” IEEE Trans. On Geoscience and Remote Sensing , vol. 48, no. 2, Feb. 2010.
    4. 4. *M. Bara, R. Scheiber, A. Broquetas and A. Moreira, “Interferometric SAR Signal Analysis in the Presence of Squint,” IEEE Trans. On Geoscience and Remote Sensing , vol. 38, no. 5, Sep. 2000. SAR Impulse Response in the Presence of Squint*
    5. 5. <ul><li>Due to the large Doppler centroid variations within a burst in the TOPS modes, small coregistration errors can introduce severe azimuth phase ramps , e.g. 0.1 samples with TerraSAR-X introduces a ramp of 1.6  within a burst (5.4 kHz Doppler variation). Therefore, an error smaller than 0.001 samples is necessary in the TerraSAR-X case to have an error smaller than 3º. </li></ul>TOPS Interferometry: Problem Statement
    6. 6. <ul><li>When using the orbit and an external DEM , very good relative accuracy can be obtained in the estimation of the range and azimuth coregistration errors. However, constant azimuth and range offsets still need to be estimated . </li></ul><ul><li>This offset comes principally from the orbit accuracy of the satellite. In TerraSAR-X the orbit position is measured with an accuracy of 5 cm (1  ) ~ 0.025 azimuth samples in stripmap, which scales to only ~0.005 azimuth samples in TOPS (which introduces a phase ramp along the burst of ~15º ). </li></ul><ul><li>Spectral diversity* (SD) has been shown to achieve the Cramér-Rao bound in the estimation of the coregistration offsets. Two approaches have been investigated based on SD. </li></ul>*R. Scheiber and A. Moreira, “Coregistration of Interferometric SAR Images Using Spectral Diversity,” IEEE Trans. On Geoscience and Remote Sensing , vol. 38, no. 5, Sep. 2000. Error: 0.05 pixels TOPS Interferometry: Problem Statement
    7. 7. *R. Scheiber and A. Moreira, “Coregistration of Interferometric SAR Images Using Spectral Diversity,” IEEE Trans. On Geoscience and Remote Sensing , vol. 38, no. 5, Sep. 2000. Look separation Coregistration error Spectral Diversity
    8. 8. <ul><li>Two approaches are suggested: </li></ul><ul><ul><li>The use of SD within one burst (conventional SD). The spectral separation between looks is given by the processed bandwidth. </li></ul></ul><ul><ul><li>The use of SD on the overlap region. The spectral separation is in this case given by the steering of the antenna. </li></ul></ul>t a f a Spectral Diversity: Approach with TOPS
    9. 9. Spectral Diversity: Performance
    10. 10. R. Bamler, M. Eineder, “Accuracy of Differential Shift Estimation by Correlation and Split-Bandwidth Interferometry for Wideband and Delta-k SAR Systems,” IEEE Geoscience and Remote Sensing Letters, vol. 2, no. 2, April 2005. Conventional SD SD with Overlap Region CRB Spectral Diversity: Performance
    11. 11. Not Corrected Corrected Results with Real Data: Mexico City (Descending)
    12. 12. 22 days repeat-pass (20.09.2009 – 12.10.2009) Results with Real Data: Mexico City (Descending) azimuth  range 
    13. 13. 5 months repeat-pass (20.09.2009 – 21.02.2010) Results with Real Data: Mexico City (Descending) azimuth  range 
    14. 14. ScanSAR – TOPS Interferogram Comparison 11-day repeat-pass TOPS SNR degradation at burst edges ScanSAR azimuth  range  azimuth  range 
    15. 15. Stripmap - TOPS DEM Comparison 11-day repeat-pass  DEM = 15m For  atm = 5mm   DEM = 27m
    16. 16. t a f a t a f a TOPS – Stripmap Interferograms: Rationale
    17. 17. 11-day repeat-pass TOPS Stripmap TOPS – Stripmap Interferograms
    18. 18. 22 days 44 days 66 days 88 days 110 days 132 days 154 days
    19. 19. 20.09.2009 – 30.01.2010 Measured subsidence
    20. 20. <ul><li>Interferometric TOPS is very sensitive to small azimuth coregistration errors , which introduce severe azimuth phase ramps . </li></ul><ul><li>A geometrical coregistration approach (DEM + orbits) is recommended  very good relative accuracy  only a constant offset in azimuth needs to be estimated, which comes from the orbit accuracy ( ~5cm in TSX  ~0.005 pixels with TOPS). </li></ul><ul><li>Two approaches based on spectral diversity have been investigated in order to estimate this offset, namely </li></ul><ul><ul><li>the use of spectral bands within bursts. </li></ul></ul><ul><ul><li>the use of the overlapping area between bursts . </li></ul></ul><ul><li>Experimental results with TSX data have been used to validate the proposed approaches, as well as a comparison with ScanSAR and stripmap. </li></ul><ul><li>TOPS - stripmap interferograms seem feasible under a PS approach. </li></ul><ul><li>The presence of an azimuth displacement might require the use of more elaborated approaches. </li></ul>Conclusion
    21. 21. Thank you for your attention!
    22. 22. 88 days 110 days 132 days 154 days 22 days 44 days 66 days
    23. 23. [1] R. Bamler, M. Eineder, “Accuracy of Differential Shift Estimation by Correlation and Split-Bandwidth Interferometry for Wideband and Delta-k SAR Systems,” IEEE Geoscience and Remote Sensing Letters, vol. 2, no. 2, April 2005. <ul><li>In [1] the performance of the spectral diversity approach is retrieved. It can be shown that the accuracy in the estimation of the differential shift in samples with non-overlapping spectra is </li></ul><ul><li>where dt is the image sampling and </li></ul><ul><li>where N is the number of averaged samples,  is the oversampling factor, B is the processed bandwidth, b is the look bandwidth, and  is the coherence. </li></ul><ul><li>The Cramér-Rao bound (CRB) in the estimation of the differential shift is met when </li></ul>Spectral Diversity: Performance
    24. 24. <ul><li>For the second approach, it can be shown that the spectral separation in the overlap region is given by </li></ul><ul><li>where Tcycle is the cycle time,  is the wavelength, v eff is the effective velocity, r rot is the rotation range, and r is the nominal range of the target. </li></ul>Spectral Diversity: Performance
    25. 25. ScanSAR – TOPS Interferogram Comparison 11-day repeat-pass ScanSAR TOPS

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