USING IMAGE SUBTRACTION AND CLASSIFICATION TO EVALUATE CHANGE IN SUBTROPICAL INTERTIDAL WETLANDS

A sub-tropical intertidal wetland in Moreton Bay, Queensland, Australi a (27 degrees 52'S, 153 degrees 23'E) was physically modified in 1985 to manage a mosquito breeding problem. Monitoring before and after mod ification was done using field and remote sensing techniques. Images f rom large scale colour infrared aerial photography were analysed to ev aluate impacts of the modification. Analysis was by subtracting and cl assifying digitized images taken before and after modification. The re sulting 'difference type images' showed the types of change and their nature. These images indicated also the spatial extent of the changes. The site has become wetter as a result of increased tidal flushing, i ndicated by reduced spectral values. The area modified has changed les s than the adjacent mangrove inlet which floods the area. Mangroves ha ve increased in size and spatial extent, with increased spectral value s generally. The changes are consistent with reported mangrove changes in other local areas and thus are unlikely to be a direct effect of r unnelling.