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USE OF RADIOMETRIC TERRAINCORRECTION TO IMPROVEPOLSAR LAND COVER CLASSIFICATION                             Don Atwood1 an...
Presentation Overview• Introduce Boreal Land Cover Classification project    • Focus on species differentiation in boreal ...
Study Region                   Boreal environment of Interior Alaska                   Characterized by:                  ...
Land Cover Reference  IGARSS July 2011   Don Atwood & David Small   4
Study Data                                 Quad-Pol data selected:                                 • ALOS L-band PALSAR   ...
Problem of TopographySpan (Trace of T3 Matrix)               Wishart Segmentation                  IGARSS July 2011   Don ...
Backscatter Reference Areas                                                   Sensor   Aβ & β0                            ...
Backscatter Reference AreasRelationships between cross sections        for ellipsoidal surfaces                       IGAR...
Terrain-flatteningThe concept of a single Local Incident Angle determining the terrain’s  local normalization area is flaw...
Terrain-flattening  Solution: Use simulated image to Normalize β0                                                         ...
Terrain-flattening Convention        1                2         3                    4               5Earth Model       No...
Terrain Correction                         in Coastal BC                         VancouverGTC (Sept 2008)                 ...
Terrain Correction                         in Coastal BCGTC (Sept 2008)                                Integrated contribu...
Coastal BC: GTCASAR WSM GTC               IGARSS July 2011   Don Atwood & David Small   14
Coastal BC: RTCASAR WSM RTC               IGARSS July 2011   Don Atwood & David Small   15
Coastal BC: NORLIMASAR WSM NORLIM             IGARSS July 2011   Don Atwood & David Small   16
Coherency Matrix                                       Scattering Matrix                                         S XX    ...
Radiometric Terrain Correction                         of Coherency Matrix• Radiometric Terrain Correction:    Coherency M...
Radiometric Terrain Correction                  of Coherency MatrixGTC: No Normalization                      RTC: Terrain...
Radiometric Terrain Correction                  of Coherency MatrixGTC: No Normalization                      RTC: Terrain...
Integration of PolSARpro                     and MapReadyIngest PALSAR data       Terrain-correct    Perform Wishart      ...
Radiometric Terrain Correction                 of Coherency MatrixWishart - No Normalization             Radiometric Terra...
Radiometric Terrain Correction        of Coherency MatrixUSGS Reference               Radiometric Terrain Correction      ...
Classification ResultsUrban areas missed / Identified as Open Water         IGARSS July 2011    Don Atwood & David Small  ...
Classification ResultsInability to distinguish Mixed Forests and Shrub / Scrub               IGARSS July 2011     Don Atwo...
Classification ResultsNo Normalization        USGS Reference                           RTC                   IGARSS July 2...
Accuracy Assessment                                              No Normalization                      Open        Develop...
Accuracy Assessment                                                       With RTC                      Open        Develo...
Accuracy Assessment                                 Comparison       Producer Class               RTC    No RTC           ...
Impact of RTC                   on forest classificationNo Normalization           USGS Reference                         ...
Conclusions• In general, PolSAR classification is difficult!    • Data fusion provides greatest hope for accurate classifi...
Discussion                                              Don Atwood                                              dkatwood@a...
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  1. 1. USE OF RADIOMETRIC TERRAINCORRECTION TO IMPROVEPOLSAR LAND COVER CLASSIFICATION Don Atwood1 and David Small2 1) University of Alaska Fairbanks 2) University of Zurich, Switzerland IGARSS July 2011 Don Atwood & David Small 1
  2. 2. Presentation Overview• Introduce Boreal Land Cover Classification project • Focus on species differentiation in boreal environment • Introduce reference data for land cover classification• Introduce method of Radiometric Terrain Correction (RTC) • Terrain-flattened Gamma Naught Backscatter• Perform RTC on polarimetric parameters to address topography • Demonstrate synergy of PolSARpro and MapReady Tools• Compare results for RTC-corrected and non-corrected classification• Characterize optimal classification approach for Interior Alaska IGARSS July 2011 Don Atwood & David Small 2
  3. 3. Study Region Boreal environment of Interior Alaska Characterized by: • rivers • wetlands • herbaceous tundra • black spruce forests (north facing) • birch forests (south facing) • low intensity urban areasIGARSS July 2011 Don Atwood & David Small 3
  4. 4. Land Cover Reference IGARSS July 2011 Don Atwood & David Small 4
  5. 5. Study Data Quad-Pol data selected: • ALOS L-band PALSAR • 21.5 degree look angle • Of April, May, July, and Nov dates, July 12 2009 selected • Post-thaw • Leaf-on • Coverage includes Fairbanks and regional roadsPauli Image IGARSS July 2011 Don Atwood & David Small 5
  6. 6. Problem of TopographySpan (Trace of T3 Matrix) Wishart Segmentation IGARSS July 2011 Don Atwood & David Small 6
  7. 7. Backscatter Reference Areas Sensor Aβ & β0 Aγ & γ0 Nadir Near Aσ & σ0Standard areas for Ellipsoid Normalization Far IGARSS July 2011 Don Atwood & David Small 7
  8. 8. Backscatter Reference AreasRelationships between cross sections for ellipsoidal surfaces IGARSS July 2011 Don Atwood & David Small 8
  9. 9. Terrain-flatteningThe concept of a single Local Incident Angle determining the terrain’s local normalization area is flawed: • adapted from ellipsoidal incident angle for ocean, sea-ice, & flatlands • fails to account for foreshortening and the radiometric impact of topography.To improve sensor model: ➡use local contributing area, not angle!Ref.: Small, D., Flattening Gamma: Radiometric Terrain Correction for SAR Imagery,IEEE Transactions on Geoscience and Remote Sensing, 13p (in press). IGARSS July 2011 Don Atwood & David Small 9
  10. 10. Terrain-flattening Solution: Use simulated image to Normalize β0 XExample over SwitzerlandASAR WS data courtesy ESA IGARSS July 2011 Don Atwood & David Small 10
  11. 11. Terrain-flattening Convention 1 2 3 4 5Earth Model None Ellipsoid TerrainReference AreaArea DerivationNormalisationProduct GTC NORLIM RTC IGARSS July 2011 Don Atwood & David Small 11
  12. 12. Terrain Correction in Coastal BC VancouverGTC (Sept 2008) Integrated contributing areaENVISAT ASAR WSM data courtesy ESA (based on SRTM3) IGARSS July 2011 Don Atwood & David Small 12
  13. 13. Terrain Correction in Coastal BCGTC (Sept 2008) Integrated contributing areaENVISAT ASAR WSM data courtesy ESA (based on SRTM3) IGARSS July 2011 Don Atwood & David Small 13
  14. 14. Coastal BC: GTCASAR WSM GTC IGARSS July 2011 Don Atwood & David Small 14
  15. 15. Coastal BC: RTCASAR WSM RTC IGARSS July 2011 Don Atwood & David Small 15
  16. 16. Coastal BC: NORLIMASAR WSM NORLIM IGARSS July 2011 Don Atwood & David Small 16
  17. 17. Coherency Matrix Scattering Matrix  S XX S XY  S =  S  YX SYX   S XX + SYY 2 (S XX + SYY )(S XX − SYY )* * 2 (S XX + SYY )S * XY   T3 = 1  (S − S )(S + S )* S XX − SYY 2 2 (S XX − SYY )S * XY  2  XX YY XX YY   2 S (S + S )* 2 S XY (S XX − SYY ) * 4 S XY 2   XY XX YY  T11: “Single Bounce” T22 : “Double Bounce” T33 : “Volume Scattering” IGARSS July 2011 Don Atwood & David Small 17
  18. 18. Radiometric Terrain Correction of Coherency Matrix• Radiometric Terrain Correction: Coherency Matrix terrain corrected T11 T12 T13  Coherency Matrix T3 = T21 T22 T23  T11 T12 T13  T3 = T21 T22 T23  Area Normalization     T31 T32 T33    T31 T32 T33    • Scale all matrix elements by Area Normalization • Acknowledge that angular dependence of scattering mechanisms is not addressed IGARSS July 2011 Don Atwood & David Small 18
  19. 19. Radiometric Terrain Correction of Coherency MatrixGTC: No Normalization RTC: Terrain-model Normalization IGARSS July 2011 Don Atwood & David Small 19
  20. 20. Radiometric Terrain Correction of Coherency MatrixGTC: No Normalization RTC: Terrain-model Normalization IGARSS July 2011 Don Atwood & David Small 20
  21. 21. Integration of PolSARpro and MapReadyIngest PALSAR data Terrain-correct Perform Wishart Export to GISGenerate T3 decomposition Cluster-bustingRTC using area image provided by UZHLee Sigma Speckle FilterPOC IGARSS July 2011 Don Atwood & David Small 21
  22. 22. Radiometric Terrain Correction of Coherency MatrixWishart - No Normalization Radiometric Terrain Correction IGARSS July 2011 Don Atwood & David Small 22
  23. 23. Radiometric Terrain Correction of Coherency MatrixUSGS Reference Radiometric Terrain Correction IGARSS July 2011 Don Atwood & David Small 23
  24. 24. Classification ResultsUrban areas missed / Identified as Open Water IGARSS July 2011 Don Atwood & David Small 24
  25. 25. Classification ResultsInability to distinguish Mixed Forests and Shrub / Scrub IGARSS July 2011 Don Atwood & David Small 25
  26. 26. Classification ResultsNo Normalization USGS Reference RTC IGARSS July 2011 Don Atwood & David Small 26
  27. 27. Accuracy Assessment No Normalization Open Developed Barren Deciduous Evergreen Mixed Shrub/ Woody Herbaceous User No Normalization Water Land Land Forest Forest Forest Scrub Wetlands Wetlands Accuracy Open Water 42402 22539 15229 2168 1512 99 1024 6299 498 46% Developed Land 836 27431 1304 3130 903 458 123 2663 64 74% Barren Land 0 0 0 0 0 0 0 0 0 NA Deciduous Forest 11217 50614 1795 390417 228454 112888 12687 52712 528 45% Evergreen Forest 13734 69849 6849 162366 323079 49803 12643 94157 617 44% Mixed Forest 0 0 0 0 0 0 0 0 0 NA Shrub/ Scrub 0 0 0 0 0 0 0 0 0 NA Woody Wetlands 7062 15611 4924 56052 135667 12103 30585 480635 11594 65%Herbaceous Wetlands 0 0 0 0 0 0 0 0 0 NA Producer Accuracy 56% 15% 0% 64% 47% 0% 0% 76% 0% 51% IGARSS July 2011 Don Atwood & David Small 27
  28. 28. Accuracy Assessment With RTC Open Developed Barren Deciduous Evergreen Mixed Shrub/ Woody Herbaceous User Normalized T3 Water Land Land Forest Forest Forest Scrub Wetlands Wetlands Accuracy Open Water 45570 33695 17297 3595 2188 165 1616 9905 739 40% Developed Land 942 27464 1320 4717 1547 608 148 1878 27 71% Barren Land 0 0 0 0 0 0 0 0 0 NA Deciduous Forest 10161 59438 1461 482548 234568 128097 10344 30375 147 50% Evergreen Forest 10614 50149 4409 53025 335583 30621 13520 138224 527 53% Mixed Forest 0 0 0 0 0 0 0 0 0 NA Shrub/ Scrub 0 0 0 0 0 0 0 0 0 NA Woody Wetlands 7964 15298 5614 70248 115729 15860 31434 456084 11861 64%Herbaceous Wetlands 0 0 0 0 0 0 0 0 0 NA Producer Accuracy 61% 15% 0% 79% 49% 0% 0% 72% 0% 54% IGARSS July 2011 Don Atwood & David Small 28
  29. 29. Accuracy Assessment Comparison Producer Class RTC No RTC Improvement Open Water 61% 56% 5% Developed Land 15% 15% 0% Deciduous Forest 79% 64% 15% Evergreen Forest 49% 47% 2% Woody Wetlands 72% 76% -4%• RTC yields improved accuracy (particularly for Deciduous Forest)• But statistics may not tell the whole story: the USGS reference has a stated accuracy of approximately 75%! IGARSS July 2011 Don Atwood & David Small 29
  30. 30. Impact of RTC on forest classificationNo Normalization USGS Reference RTC IGARSS July 2011 Don Atwood & David Small 30
  31. 31. Conclusions• In general, PolSAR classification is difficult! • Data fusion provides greatest hope for accurate classification results• Radiometric variability caused by topography dominates PolSAR classification• Area-based RTC offers effective way to “flatten” SAR radiometry• RTC of Coherency Matrix shown to improve classification accuracy: • Impact most pronounced for Deciduous Forests• Although not complete, RTC approach is simple and effective • Different scattering mechanisms (SB, DB, Volume) have different sensitivities to topography. RTC does not address this • However, RTC is very effective first order correction for segmenting polarimetric data by phenology rather than topography IGARSS July 2011 Don Atwood & David Small 31
  32. 32. Discussion Don Atwood dkatwood@alaska.edu (907) 474-7380 32 IGARSS July 2011 Don Atwood & David SmallPhoto Credit: Don Atwood
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