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NATURAL ENVIRONMENT CHANGE DETECTION IN DANUBE DELTA , BASED ON HRV-SPOT IMAGES

The Danube Delta is an area with a unique ecological signification, which present accentuated interest from scientific, tourist and even economically. His complex and varieties ecosystems have remained unspoiled for centuries, natives integrating in preserving of natural balance. In the last 3-4 decades, a dramatic alteration be cause of accentuated human intervention in Danube area, inside Danube Delta’s and in coastal area of Black Sea. In this context, a study on change-detection occurred at the level of principal morphological elements and vegetation has been achieved in a site, which contain approximate 70% of delta’s surface. The study is based on two HRV SPOT images, acquired in May 27, 1986 and April 27, 1993. Two different methods have been used for change detection: vegetation index comparison and post-classification achieved based on the composite images. A Normalized Difference Vegetation Index (NDVI) has been computed for each image; then the new images have been compared by difference in first case. Using the second method, composite images are generated from the two principal components on which are added Normalized Difference Vegetation Index (NDVI). Furthermore, these images are submitted a hybrid classification process, followed by a modal type filtering. Finally, the classified and filtered images are compared by difference. The study first revealed the utility of HRV SPOT images for delta’s environment monitoring. Between two methods used, more accurately results give comparison post classification of composite images. The accuracy is improved significantly if the threshold value of mode filters is choused according.