Determination of the upper boundary of a Posidonia meadow

The sensitivity of Posidonia oceanica at environmental variations is well known since long time. The capability of quantifying environmental space-time modification is very interesting in order to establish seagrasses cover changes. The use of aerial colour photos, after the necessary manipulations, can be useful for investigative aims. Thanks to ortorectification and mosaicing processes, a georeferenced space representative of the study area is reconstructed without optical distortions. The images are processed to highlight the area covered by P. oceanica and the récif barrière in particular. This permitted to obtain a set of themes representative of the underwater vegetable cover and to analyze the space-time changes between 1987 and 1999.