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Visual Interpretation for Forest Change Detection in Fiji

Visual Interpretation for Forest Change Detection in Fiji. Vilisi Tokalauvere SOPAC Pacific GIS&RS Conference November 2011 Lotus Building, Suva. Purpose of Forest Mapping. Direct comparison of digital forest layers 1991 and 2001 did not work

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Visual Interpretation for Forest Change Detection in Fiji

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  1. Visual Interpretation for Forest Change Detection in Fiji Vilisi Tokalauvere SOPAC Pacific GIS&RS Conference November 2011 Lotus Building, Suva

  2. Purpose of Forest Mapping • Direct comparison of digital forest layers 1991 and 2001 did not work • Layer 1991 and layer 2001 had to be adjusted through visual image interpretation • Forest layers 1991 and 2001 had to be geometrically corrected

  3. Why visual interpretation? • Pacific Island Country conditions are different! • Transparent work • Local knowledge added • Difficult atmospheric conditions

  4. Forest Cover Mapping 1991 • Supervised maximum likelihood classification with DTM involvement • Conducted by a company in northern Germany

  5. Forest FunctionMap 1992 Raster data GIS application

  6. Forest Inventory 2006 • Conducted with image data recorded 2001/2002 • Condition maximum likelihood classification • Solution: Unsupervised classification with maximum visual interaction • Mask building • Reducing 3 forest densities (1991) to 2

  7. Water Mask Applied

  8. Digitising in MapInfo

  9. ERDAS Mangrove Mask Mangrove mask Vanua Levu

  10. Haze Different thresholds

  11. Visual Interpretation Pine Plantation Mangrove Forest

  12. Digitising

  13. Decisions During Digitising Digitising from Forest Layer 1991 Yes Clouds Y/N ? No Digitising from Plantation Layer 1991 Plantation area Y/N ? Yes No Digitising from both image backdrops

  14. Toggle between Backdrops

  15. Digitising 1991 Layer

  16. Digitising 2001 Forest Layer

  17. 10x 10 km GRID

  18. Description Database

  19. Vector to Raster

  20. MapInfo to ERDAS • Forest, Mangrove polygons exported (DXF) to ERDAS. • Add Projection. • Convert to raster. • Add to forest cover layer.

  21. Reducing to Mappable Area Size Cluster No. 2384 1.2 ha Clump All clusters < 1 hectare are joined with the next biggest neighbour class Eliminate

  22. 1Hectare Accumulation

  23. Field Verification

  24. Next.. • Fiji Department of Agriculture – agriculture, bare land, pasture land

  25. Vinaka !

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