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 workDirect comparison of digital forest layers 1991 and 2001 did not work Layer 1991 and layer 2001 had to be adjusted through visual image interpretationLayer 1991 and layer 2001 had to be adjusted through visual image interpretation Forest layers 1991 and 2001 had to be geometrically correctedForest layers 1991 and 2001 had to be geometrically corrected

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

Forest Cover Mapping 1991 Supervised maximum likelihood classification with DTM involvementSupervised maximum likelihood classification with DTM involvement Conducted by a company in northern GermanyConducted by a company in northern Germany

Forest Function Map 1992 Raster data GIS application

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

Water Mask Applied

Digitising in MapInfo

ERDAS Mangrove Mask Mangrove mask Vanua Levu

HazeHaze Different thresholds

Visual Interpretation MangroveForest Pine Plantation

Digitising

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

Toggle between Backdrops

Digitising 1991 Layer

Digitising 2001 Forest Layer

10x 10 km GRID

Description Database

Vector to Raster

MapInfo to ERDAS Forest, Mangrove polygons exported (DXF) to ERDAS.Forest, Mangrove polygons exported (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 Area Size Clump Eliminate Cluster No ha All clusters < 1 hectare are joined with the next biggest neighbour class

1Hectare Accumulation

Field Verification

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

Vinaka !