Use of stereo aerial photography for assessing changes in the extent and height of mangrove canopies in tropical Australia

This paper examines the use of time-series of stereo aerial photographs for quantifying changes in the extent and height of mangrove communities. For the West Alligator River, Kakadu National Park, Australia, black and white and colour stereo aerial photographs of mangroves were acquired in 1950 and 1991 respectively. Digital ortho-images were generated for each date, and maps of mangrove extent were obtained by applying an unsupervised classification to each image. Digital elevation models (DEMs) of the mangrove canopy were derived from the stereo pairs. The comparison of mangrove extent suggested that substantial changes had occurred over the 41-year period, largely in response to saltwater intrusion. Changes in the height of mangroves were also observed but were difficult to quantify due to the poor quality of the 1950 DEM. The study concludes that time-series comparisons of aerial photographs are invaluable for assessing change in mangroves over periods of up to 4-5 decades