Visual Interpretation for Forest Change Detection in Fiji

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

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• Fiji Department of Agriculture – Fiji Department of Agriculture – agriculture, bare land, pasture landagriculture, bare land, pasture land

Vinaka !Vinaka !