Monitoring seasonal dynamics of Northern Australian wetlands with multitemporal Radarsat data

Northern Australia exhibits an extremely seasonal climate and this is reflected in the change in vegetation communities present in a given area of wetland. The monsoonal nature of this climate means a huge variation in the amount of water available to plant life both on and surrounding the floodplains of the major river systems. Kakadu National Park, a heritage listed and Ramsar identified wetland of international significance, has a long history of scientific study an ideal study site on which to conduct studies such as this. Changes within the wetland areas in the park have been noted since the early 1980s, but have been poorly quantified. Many of the changes are related to the timing of the onset of the monsoon, the period of inundation and the location of the major flooding. However neither multispectral or hyperspectral sensors are able to capture information at the onset of the monsoon due to perpetual cloud coverage. Radar has the unique ability to image through cloud and hence 27 Standard and ScanSAR images were collected over the region from 1996 to 2001. The majority of the images were S4 ascending, with ScanSAR narrow collected simultaneously. The images were co-registered allowing comparison of the same geographic location through time. The simultaneous ScanSAR images allowed assessment of the technique over a wider swath, yielding results on a regional rather than local scale. Radar reflection is intimately related to the moisture content of the target due to the influence of moisture upon the dielectric constant. A modified Gaussian Markov Random Field Model Segmentation was used to cluster areas exhibiting similar radar response at each successive date in the time series. The ability to segment and extract reflection statistics for the same geographic location for each image in the series allows the construction of temporal curves, indicating change in the target material´s dielectric constant over time.