1. The context.

Previous studies both remote sensing and otherwise, have shown the disappearance of the Ried prairies in Alsace, which are now the subject of a regional authority-farmer preservation contract, started in 1992.

Year	  Prairie surface	Remote sensing data
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1978         12 130 ha          Landsat MSS du 8 avril 1978  
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1984          6 100 ha          Landsat TM du 17 octobre 1984
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1989          2 870 ha          Landsat TM du 6 mars 1989
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With regional subsidies involved in compensating farmers for set-a-side land, this seems an opportune moment to test remote sensing data and Geographical Information Systems (GIS) applied to regional authority subvention monitoring in the framework of the common agriculture policy (PAC).

The main aims of these policies is to protect the ecological value and the ground water quality of the area.