1. Don Atwood & David SmallIGARSS July 2011 1 USE OF RADIOMETRIC TERRAIN CORRECTION TO IMPROVE POLSAR LAND COVER CLASSIFICATION USE OF RADIOMETRIC TERRAIN CORRECTION TO IMPROVE POLSAR LAND COVER CLASSIFICATION Don Atwood 1 and David Small 2 1)University of Alaska Fairbanks 2)University of Zurich, Switzerland

2. Don Atwood & David SmallIGARSS July 2011 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

3. Don Atwood & David SmallIGARSS July 2011 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 areas

4. Don Atwood & David SmallIGARSS July 2011 4 Land Cover Reference

5. Don Atwood & David SmallIGARSS July 2011 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 roads Pauli Image

6. Don Atwood & David SmallIGARSS July 2011 6 Problem of Topography Span (Trace of T3 Matrix) Wishart Segmentation

7. Don Atwood & David SmallIGARSS July 2011 7 Normalized Radar Cross Sections Nadir Sensor Far Near A σ & σ 0 A γ & γ 0 A β & β 0 Let’s compute Normalized Radar Cross Sections for an Ellipsoidal Earth for Topography

8. Don Atwood & David SmallIGARSS July 2011 8 Relationships between cross sections for ellipsoidal surfaces Backscatter Reference Areas For an Ellipsoidal Earth

9. Don Atwood & David SmallIGARSS July 2011 9 Terrain-flattening We need to move beyond the ellipsoidal Earth to the hills and valleys of the Fairbanks region: Address the layover and foreshortening of geometric distortions Correct the radiometric variations associated with topography. To improve our radiometry: ➡ use local area contributing to backscatter at each location in the SAR scene

10. Don Atwood & David SmallIGARSS July 2011 10 Terrain-flattening Convention12345 Earth ModelNoneEllipsoidTerrain Reference Area Area Derivation Normalisation Product GTC NORLIM RTC

11. Don Atwood & David SmallIGARSS July 2011 11 Ref.: Small, D., Flattening Gamma: Radiometric Terrain Correction for SAR Imagery, IEEE Transactions on Geoscience and Remote Sensing, 13p (in press). Terrain-flattening X Solution: Use simulated image to Normalize β 0

12. Don Atwood & David SmallIGARSS July 2011 12 Vancouver GTC (Sept 2008)Integrated contributing area ENVISAT ASAR WSM data courtesy ESA(based on SRTM3) Terrain Correction in Coastal BC

13. Don Atwood & David SmallIGARSS July 2011 13 Terrain Correction in Coastal BC GTC (Sept 2008)Integrated contributing area ENVISAT ASAR WSM data courtesy ESA(based on SRTM3)

14. Don Atwood & David SmallIGARSS July 2011 14 ASAR WSM GTC Coastal BC: GTC

15. Don Atwood & David SmallIGARSS July 2011 15 ASAR WSM RTC Coastal BC: RTC

16. Don Atwood & David SmallIGARSS July 2011 16 ASAR WSM NORLIM Coastal BC: NORLIM

17. Don Atwood & David SmallIGARSS July 2011 17 Coherency Matrix Scattering Matrix : “Single Bounce” : “Double Bounce” : “Volume Scattering”

18. Don Atwood & David SmallIGARSS July 2011 18 Radiometric Terrain Correction of Coherency Matrix Radiometric Terrain Correction: Area Normalization terrain corrected Coherency Matrix Coherency Matrix Scale all matrix elements by Area Normalization

19. Don Atwood & David SmallIGARSS July 2011 19 For a given class, the ratio of Surface, Double Bounce, and Volume scattering components depend on incidence angle POLARIMETRIC IMPLICATIONS OF INCIDENCE ANGLE VARIABILITY FOR UAVSAR Guritz, Atwood, Chapman, and Hensley But Wait…..

20. Don Atwood & David SmallIGARSS July 2011 20 Radiometric Terrain Correction of Coherency Matrix Span: No Normalization Span: Terrain-model Normalization

21. Don Atwood & David SmallIGARSS July 2011 21 Radiometric Terrain Correction of Coherency Matrix Pauli: No Normalization Pauli: Terrain-model Normalization

22. Don Atwood & David SmallIGARSS July 2011 22 Ingest PALSAR data Terrain-correct Perform Wishart Export to GIS Generate T3 with MapReady decomposition Cluster-busting Radiometric correction using area Lee Sigma Speckle Filter POA compensation Integration of PolSARpro and MapReady

23. Don Atwood & David SmallIGARSS July 2011 23 Radiometric Terrain Correction of Coherency Matrix Wishart - No Normalization Wishart - Radiometric Correction

24. Don Atwood & David SmallIGARSS July 2011 24 Radiometric Terrain Correction of Coherency Matrix USGS Reference Wishart – Radiometric Correction

25. Don Atwood & David SmallIGARSS July 2011 25 Classification Results No Normalization USGS Reference RTC

26. Don Atwood & David SmallIGARSS July 2011 26 Classification Results Urban areas missed / Identified as Open Water

27. Don Atwood & David SmallIGARSS July 2011 27 Classification Results Inability to distinguish Mixed Forests and Shrub / Scrub

28. Don Atwood & David SmallIGARSS July 2011 28 Accuracy Assessment No Normalization Open Water Developed Land Barren Land Deciduous Forest Evergreen Forest Mixed Forest Shrub/ Scrub Woody Wetlands Herbaceous Wetlands User Accuracy Open Water42402225391522921681512991024629949846% Developed Land836274311304313090345812326636474% Barren Land000000000NA Deciduous Forest11217506141795390417228454112888126875271252845% Evergreen Forest1373469849684916236632307949803126439415761744% Mixed Forest000000000NA Shrub/ Scrub000000000NA Woody Wetlands70621561149245605213566712103305854806351159465% Herbaceous Wetlands000000000NA Producer Accuracy56%15%0%64%47%0% 76%0%51%

29. Don Atwood & David SmallIGARSS July 2011 29 Accuracy Assessment With RTC Normalized T3 Open Water Developed Land Barren Land Deciduous Forest Evergreen Forest Mixed Forest Shrub/ Scrub Woody Wetlands Herbaceous Wetlands User Accuracy Open Water455703369517297359521881651616990573940% Developed Land9422746413204717154760814818782771% Barren Land000000000NA Deciduous Forest10161594381461482548234568128097103443037514750% Evergreen Forest1061450149440953025335583306211352013822452753% Mixed Forest000000000NA Shrub/ Scrub000000000NA Woody Wetlands79641529856147024811572915860314344560841186164% Herbaceous Wetlands000000000NA Producer Accuracy61%15%0%79%49%0% 72%0%54%

30. Don Atwood & David SmallIGARSS July 2011 30 Accuracy Assessment Comparison Producer ClassRTCNo RTCImprovement Open Water61%56%5% Developed Land15% 0% Deciduous Forest79%64%15% Evergreen Forest49%47%2% Woody Wetlands72%76%-4% RTC yields improved accuracy (particularly for Deciduous Forest)

31. Don Atwood & David SmallIGARSS July 2011 31 Impact of RTC on forest classification No Normalization USGS Reference RTC

32. Don Atwood & David SmallIGARSS July 2011 32 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

33. Don Atwood & David SmallIGARSS July 2011 33 Discussion Don Atwood dkatwood@alaska.edu (907) 474-7380 Photo Credit: Don Atwood