Large-scale land use by teledetection (projected on Rhône-Alpes)

CEREMA worked in 2013 as part of an exploratory study for DREAL Rhônes Alpes, DRAAF Rhône-Alpes and the Auvergne-Rhône-Alpes Regional Council (Auvergne-Rhône-Alpes Region) on the semi-automatic implementation of a first-level land use layer in 3 test territories using satellite images. The objective of the method is to assist the departments in charge of territorial planning in calculating the quantified indicators characterising land use and its evolution in order to meet the regulatory requirements in this area. The method of layer construction consists of combining automatic extraction of information from satellite images (supervised classifications) and post-processed information from existing databases (BD Topo, RPG...). If the construction process differs from the IGN process for the implementation of the future OCS Grande Scale layer, and if the specification of the layer is less ambitious, the objective is to have a layer consistent with the national benchmark: compatible nomenclature, use of the same structural skeleton of the territory, same minimum collection unit etc... The value of such data lies in the following points: — temporal homogeneity of source information (the satellite images used — RapidEye Images at 5 m of resolutions from the GEOSUD programme) are acquired in the national territory a few months apart; — possibility of annual updating, as a result of the annual update of the national satellite coverage and the use of automated processes; — limited costs (satellite images are available free of charge to institutional users, and process automation reduces the human time required for photo-interpretation methods for example); — response to a first level of needs (zero state of the “natural structure” and “urban reinforcement”, quantification of the distribution of urban or natural areas, quantification of the effectiveness of different planning measures taken, etc.) It is presented in 7 soil cover classes: Anthropogenic surfaces, Transportation infrastructure, bare soils, Water surfaces, Eternal Snows and Glacier, Woody Vegetation and Non-woody Vegetation. The product is delivered in vector format with a minimum collection unit (UMC, size of the smallest polygons) of 500 m². This transition from a 5 m resolution image to an UMC 500 m² implies a generalisation of the geometry of the objects represented, which is particularly noticeable on the linear elements of the landscape (mainly discontinuity of the road network). Where available, the information for use is also specified in a raster layer of 25 m². It is divided into 6 classes: Agriculture, Mines and quarries, Secondary production, tertiary or residential use, Road, Ferré, Aérien. The product is delivered by department, according to the right-of-way defined in the CARTO® BD (ongoing homogenisation, the department of Drôme having been delivered to the GEOFLA® right-of-way).