Monitoring Wetland Change Using Inter-Annual Landsat Time-Series Data

Successful conservation and management of wetlands requires up-to-date and accurate information on wetland location, size, condition, functionality, type, services provided, stressors and net change in extent. Most change detection studies utilize two date images to provide information on wetland dynamics. Comparison of infrequent imagery might not sufficiently capture natural variability in wetlands. Use of longer time series of images might increase our ability to characterize the temporal variability of wetland and detect changes with greater accuracy. We used inter-annual time series of Landsat data from 1985 to 2009 to map changes in wetland ecosystems in northern Virginia. Z-scores calculated on tasseled cap images were used to develop temporal profile for wetlands delineated by the National Wetland Inventory. A change threshold was derived based on the Chi-square distribution of the Z-scores. The accuracy of a change/no change map produced was 89 % with a kappa value of 0.79. Assessment of the change map showed that the method was able to detect complete wetland loss together with other subtle changes resulting from development, harvesting, thinning and farming practices. With additional research on attributing the change events, the method may provide more detailed information on status and the trends of wetland loss and functioning.