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Visual Interpretation for Visual Interpretation for Forest Change Detection in Forest Change Detection in
FijiFiji
Vilisi TokalauvereVilisi Tokalauvere
SOPACSOPACPacific GIS&RS ConferencePacific GIS&RS Conference
November 2011November 2011
Lotus Building, SuvaLotus Building, Suva
Purpose of Forest MappingPurpose of Forest Mapping
• Direct comparison of digital forest Direct comparison of digital forest layers 1991 and 2001 did not worklayers 1991 and 2001 did not work
• Layer 1991 and layer 2001 had to be Layer 1991 and layer 2001 had to be adjusted through visual image adjusted through visual image interpretationinterpretation
• Forest layers 1991 and 2001 had to Forest layers 1991 and 2001 had to be geometrically correctedbe geometrically corrected
Why visual Why visual interpretation? interpretation?
•Pacific Island Country Pacific Island Country conditions are different!conditions are different!–Transparent workTransparent work–Local knowledge addedLocal knowledge added–Difficult atmospheric Difficult atmospheric conditionsconditions
Forest Cover Mapping 1991Forest Cover Mapping 1991
•Supervised maximum Supervised maximum likelihood classification with likelihood classification with DTM involvementDTM involvement
•Conducted by a company in Conducted by a company in northern Germanynorthern Germany
Forest FunctionForest FunctionMap 1992Map 1992
Raster data GIS applicationRaster data GIS application
Forest Inventory 2006Forest Inventory 2006• Conducted with image data recorded Conducted with image data recorded
2001/20022001/2002• Condition maximum likelihood Condition maximum likelihood
classification classification • Solution: Unsupervised classification Solution: Unsupervised classification
with maximum visual interaction with maximum visual interaction • Mask buildingMask building• Reducing 3 forest densities (1991) to 2Reducing 3 forest densities (1991) to 2
Water Mask AppliedWater Mask Applied
Digitising in MapInfoDigitising in MapInfoDigitising in MapInfoDigitising in MapInfo
ERDAS Mangrove MaskERDAS Mangrove Mask
Mangrove mask Vanua Levu
HazeHazeHazeHaze
Different thresholds
Visual InterpretationVisual Interpretation
Mangrove Forest
Pine Plantation
DigitisingDigitising
Decisions During DigitisingDecisions During Digitising
Clouds Y/N ?Clouds Y/N ? YesYes Digitising from Forest Digitising from Forest Layer 1991Layer 1991
NoNo
Digitising from Digitising from PlantationPlantationLayer 1991Layer 1991
YesYesPlantation area Y/N ?Plantation area Y/N ?
Digitising from both image backdropsDigitising from both image backdrops
NoNo
Toggle between BackdropsToggle between Backdrops
Digitising 1991 LayerDigitising 1991 Layer
Digitising 2001 Forest LayerDigitising 2001 Forest Layer
10x 10 km GRID10x 10 km GRID
Description DatabaseDescription Database
Vector to RasterVector to Raster
MapInfo to ERDASMapInfo to ERDAS
• Forest, Mangrove polygons exported Forest, Mangrove polygons exported (DXF) to ERDAS.(DXF) to ERDAS.
• Add Projection.Add Projection.• Convert to raster.Convert to raster.• Add to forest cover layer. Add to forest cover layer.
Reducing to Mappable Reducing to Mappable Area Size Area Size
ClumpClump
EliminateEliminate
Cluster No. 23841.2 ha
All clusters < 1 hectare are joined with the next biggest neighbour class
1Hectare Accumulation1Hectare Accumulation1Hectare Accumulation1Hectare Accumulation
Field VerificationField Verification
Next..Next..
• Fiji Department of Agriculture – Fiji Department of Agriculture – agriculture, bare land, pasture landagriculture, bare land, pasture land
Vinaka !Vinaka !