Salinity monitoring in Western Australia using remotely sensed and other spatial data.

The southwest of Western Australia is affected by dryland salinity that results in the loss of previously productive agricultural land, damage to buildings, roads, and other infrastructure, decline in pockets of remnant vegetation and biodiversity, and reduction in water quality. Accurate information on the location and rate of change of the extent of saline land over the region is required by resource managers. For the first time, comprehensive, spatially explicit maps of dryland salinity and its change over approximately 10 yr for the southwest agricultural region of Western Australia have been produced operationally in the 'Land Monitor' project. The methods rely on an integrated analysis of long-term sequences of Landsat TM satellite image data together with variables derived from digital elevation models (DEMs). Understanding of the physical process and surface expression of salinity provided by experts was used to guide the analyses. Ground data-the delineation of salt-affected land by field experts-was collected for training and validation. The results indicate that the land area currently affected by salinity in Western Australia's southwest is about 1 million hectares (in 1996) and the annual rate of increase is about 14,000 ha. This is a lesser extent than many previous estimates and lower rate of change than generally predicted from limited hydrological data. The results are widely distributed and publicly available. The key to providing accurate mapping and monitoring information was the incorporation of time series classification of a sequence of images over several years combined with landform information.