Land cover mapping of Victoria, 2015

Abstract

Land cover mapping data is an annual component of the Victorian Land Use Information System, the VLUIS (refer to separate record). The land cover information has been created specifically for the VLUIS using time series analysis of the MOD13Q1 product produced by NASA using data collected by the MODIS sensor and freely available on the Reverb | ECHO website. Ground data is collected annually across Victoria using a stratified random sampling approach for calibration of the annual seasonal curves and validation of the classification output. The ground data is split into three groups with 50% used to develop classification rules, 25% used to produce interim validation results that feed back into the rule development process with the remaining 25% used to independently validate the final classification. Error matrices for each land cover dataset from 2009 have been produced from this final validation. No ground data was available prior to 2009 and so error matrices do not exist. The TIMESAT GUI is used to create smoothed annual time series for the Normalised Differenced Vegetation Index (NDVI) and the Red and Near Infrared (NIR) MOD13Q1 bands using the Savitsky-Golay algorithm. A suite of 11 seasonal parameters are created that each numerically describe features of the annual seasonal curves for each band. In addition the standard deviation of the annual seasonal curve is calculated for each band and used in conjunction with the seasonal parameters. Prior to classification, the ground data and the MOD13 data is stratified into regions with similar climate, soils and farming systems using the Primary Production landscapes developed by DEDJTR. For each stratified region a three-tiered hierarchical classification was developed to assign a dominant land cover class to each pixel. Initially, rules developed using expert knowledge were applied to the seasonal parameters and the annual standard deviation in conjunction with a GIS data-set of water bodies greater than 12.5ha in area to classify each pixel as either Tree, Non-tree or Water based on two data sets from the Victorian spatial data library, HY_WATER_AREA_POLY.shp and VM_LITE_HY_WATER_AREA.shp; and are combined to form the water bodies layer. In addition, the primary classes are cross checked using data from preceding and following years to reduce misclassification prior to the secondary classification. A secondary classification developed using rules based on expert knowledge is applied to split the primary class Tree into the secondary classes Native Woody Cover and Treed Production and the primary class Non-tree into the secondary classes Pasture/ Grassland and Crops. Finally, a tertiary classification further divides the secondary class Treed Production into the tertiary classes Hardwood Plantation, Softwood Plantation and Woody Horticulture and the secondary class Crops into the tertiary classes Brassicas, Legumes, Cereals and Non-Woody Horticulture based on rules developed using the data mining tool See5 and modified where appropriate by expert knowledge. This tertiary classification is not available for the 2006 to 2008 data. A mask has been applied to remove 'urban' pixels that comprise land parcels less than 6.25 Ha in size.