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DC Estimation Accuracy

DC Estimation Accuracy. DCE in IM mode Overview of DC estimation in IM mode Design of a Verification Mode DC Estimator (VMDCE) VMDCE validation PF-ASAR DC estimate accuracy and offset constant DCE in WSM Design of a DC in WSM Impact of DC estimate. f x =-2v/ l sin( y ( l ) ). y.

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DC Estimation Accuracy

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  1. DC Estimation Accuracy • DCE in IM mode Overview of DC estimation in IM mode Design of a Verification Mode DC Estimator (VMDCE) VMDCE validation PF-ASAR DC estimate accuracy and offset constant • DCE in WSM Design of a DC in WSM Impact of DC estimate

  2. fx=-2v/l sin(y(l)) y frequency Amplitude What’s “Doppler Centroid” ? The  linear frequency-angle provided by the SAR array converts the azimuth beam center into the Doppler centroid.

  3. PSD PRF fDC DC estimate (ambiguous) DC knowledge is fundamental for calibration and processing. It can be retrieved by IInd order techniques. This estimate is however ambiguous by multiple of PRF. T.B. Pickard The effect of noise upon a method of frequency measurement. IRE Trans. Inf, Jun 1958

  4. DC estimate (ambiguous) • The accuracy of DC estimate is strongly dependent on: • the presence of contrasts • the SNR y0 Contrasts reduce the variance and may introduce bias, particularly on range compressed data.

  5. DC Biasing on range compressed data

  6. DC Biasing on range compressed data

  7. DC Biasing on range compressed data

  8. DC Biasing on range compressed data

  9. DC Biasing on range compressed data

  10. DC Biasing on range compressed data

  11. Issues on DC estimate • In the real SAR case, DC is range and azimuth varying (+ wrapped). • Large errors may be introduced if “unwrapping” is performed. They can be avoided by fitting a wrapped model. • PF-ASAR assumes fdc = const with azimuth

  12. Netherlands, IS2 Rain Forest, IS5 DC estimate: accuracy

  13. 8-16 MHz fx fDC PRF k PRF 2v/c•0 fDCa f Base-band domain DC estimate: unambiguous The unambiguous DC can be retrieved by finding the spectral slope fx at different l: fx=-2v/l sin(y(l)) 0.32 Hz / MHz There is an offset constant to be calibrated !

  14. A different approach The unambiguous DC can also be retrieved by exploiting the frequency dependence of the IRF (the range migration). We need just a strong point scatterer or, in general, a NON-Gaussian source. Dt

  15. Ambiguity Resolving: Summary • Spectral slope • needs 2nd order techniques, that requires homogeneous scenes • there is an offset constant to be calibrated. It may change with antenna configuration (swath, pol, mode, ?) • IRF shape • implemented as blind deconvolution (High Order Statistics), hence contrasted scenes. It not works with homogeneous scenes. • no offset frequency. • The two techniques are complementary and should be both implemented, basing on local contrasts.

  16. Ambiguity retrieval VM DC Estimator (Polimi) Unambiguous DC estimate Ambiguous DC estimate (blockwise) Ambiguous DC: polynomial fit + Range Compr. Data Unambiguous DC estimate (blockwise) -

  17. Range Compr. Data Weigthed wrapped polynomial regression Estimate DC ambiguous Blocks division Estimate SNR Estimate contrast index Blind. Deconv. (MLBF) Coarse DC estimate Select ambiguity resolver Fine absolute DC retreiving Power Spectrum (WDAR) Block processing Polynomial coeff. + offset frequency

  18. VMDCE:Validation • The Verification Mode Doppler Centroid Estimator has been inserted into the core SAR processor at TRE. It required only some initial tuning / setting (to account for saturation and other 2nd order effects). Massive processing of ERS scenes since July 2002, with ambiguity up to 10. • Validation included comparison with PF-ERS in strip-mode / investigation on an anomalous dataset. • The processor has been upgraded to ENVISAT level-zero data by the end of August. • DC estimate (polynomial), accuracy and offset constant are now automatically generated out of ASA_IM__0 • There is an open issue on focused data timing, that do not affect appreciably the estimate.

  19. Sea histogram 80 70 45 Hz 60 50 Land histogram 40 30 20 10 0 0 50 100 150 200 VMDCE & PF-ERS

  20. VMDCE: Validation Comparsion between PF-ERS estimates and VMDCE in stripmap data DC Anomaly • = 13 Hz (PF-ERS) s = 3 Hz (VMDCE)

  21. Observed: August 20,1995 Marseille Observed: August 20,1995 Montpellier Mean Temperature 78.4° F Mean Temperature 77.6° F Max Temperature 91.4° F Max Temperature 91.2° F Min Temperature 67.1° F Min Temperature 66.2° F Cooling Degree Days 14 Cooling Degree Days 13 Growing Degree Days 19 (base 60°F) Growing Degree Days 18 (base 60°F) Dewpoint 58.7° F Dewpoint 63.6° F Precipitation 0.0 in Precipitation 0.0 in Snow Depth N/A Snow Depth N/A Sea Level Pressure 29.96 in Sea Level Pressure 29.94 in Standard Pressure 29.94 in Standard Pressure 29.81 in Visibility 8.60 mi Visibility 7.50 mi Wind Speed 7.37mph Wind Speed 10.24 mph Max Wind Speed 18.30mph Max Wind Speed 19.45 mph Gust Speed N/A Gust Speed N/A Events Rain, Thunderstorms  Events

  22. Suggested improvement to PF-ASAR processor

  23. PF-ASAR DC accuracy: First Results Offset frequency scaled of 3 / 6 kHz after antenna upgrade Jul 2002

  24. ASAR DC estimate: Rain Forest

  25. PF-ASAR accuracy: worst case

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