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  • 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. 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. 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. Land Cover Reference IGARSS July 2011 Don Atwood & David Small 4
  • 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. Problem of TopographySpan (Trace of T3 Matrix) Wishart Segmentation IGARSS July 2011 Don Atwood & David Small 6
  • 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. Backscatter Reference AreasRelationships between cross sections for ellipsoidal surfaces IGARSS July 2011 Don Atwood & David Small 8
  • 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. 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. 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. 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. 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. Coastal BC: GTCASAR WSM GTC IGARSS July 2011 Don Atwood & David Small 14
  • 15. Coastal BC: RTCASAR WSM RTC IGARSS July 2011 Don Atwood & David Small 15
  • 16. Coastal BC: NORLIMASAR WSM NORLIM IGARSS July 2011 Don Atwood & David Small 16
  • 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. 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. Radiometric Terrain Correction of Coherency MatrixGTC: No Normalization RTC: Terrain-model Normalization IGARSS July 2011 Don Atwood & David Small 19
  • 20. Radiometric Terrain Correction of Coherency MatrixGTC: No Normalization RTC: Terrain-model Normalization IGARSS July 2011 Don Atwood & David Small 20
  • 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. Radiometric Terrain Correction of Coherency MatrixWishart - No Normalization Radiometric Terrain Correction IGARSS July 2011 Don Atwood & David Small 22
  • 23. Radiometric Terrain Correction of Coherency MatrixUSGS Reference Radiometric Terrain Correction IGARSS July 2011 Don Atwood & David Small 23
  • 24. Classification ResultsUrban areas missed / Identified as Open Water IGARSS July 2011 Don Atwood & David Small 24
  • 25. Classification ResultsInability to distinguish Mixed Forests and Shrub / Scrub IGARSS July 2011 Don Atwood & David Small 25
  • 26. Classification ResultsNo Normalization USGS Reference RTC IGARSS July 2011 Don Atwood & David Small 26
  • 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. 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. 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. Impact of RTC on forest classificationNo Normalization USGS Reference RTC IGARSS July 2011 Don Atwood & David Small 30
  • 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. Discussion Don Atwood dkatwood@alaska.edu (907) 474-7380 32 IGARSS July 2011 Don Atwood & David SmallPhoto Credit: Don Atwood