Update of the European High-resolution Layer on Built-up Areas and Soil Sealing 2006 with Image2009 Data

The European Environment Agency (EEA) requested from the FP7 geoland2 project a year 2009 update of the European high resolution layer on built-up areas and soil sealing, which was derived from the IMAGE2006 satellite coverage. Methodological development of the automated change detection approach is covered by the Core Mapping Service (CMS) EUROLAND, which further develops the GMES Land Monitoring Core Service, including advanced approaches for continental land cover and land cover change mapping. The objective is to derive a comparable product of highest possible quality, showing changes of the built-up area between 2006 and 2009 as well as changes in the sealing degree within the 2006 sealed surfaces in 1ha resolution. As for the 2006 soil sealing layer, bi-temporal Spot and IRS-P6 satellite data with a nominal pixel size of 20m (IMAGE2009) are being used. The 2006 built-up layer resulted from a combined approach based on automatic image classification and subsequent visual post-classification editing. Corresponding sealing degrees (1% to 100% sealing with 1 % increments) were derived based on vegetation indexes (NDVIs) calculated from the satellite imagery with a calibration approach applied individually to each data set.

Starting point is the automated derivation of 2006-2009 changes of the built-up area. This task is solved with a change detection approach, which follows a similar methodology as for the 2006 mapping in order to guarantee the highest possible degree of consistency and comparability of these products. The built-up area change detection would work in a comparable way for all European landscapes using standard change detection and mapping techniques. However, the update of the sealing degrees is a more challenging and complex task as it includes both the determination of sealing degrees of newly built-up areas, consistent with the original product, as well as the derivation of sealing changes within areas previously assigned as built-up ones. Thus the sealing update methodology depends on an adaptation of the 2009 NDVIs to the 2006 sealing degrees. For this purpose a procedure was developed that automatically derives adapted sealing degrees from the 2009 NDVIs via a series of histogram matching steps, taking into account the partly non-linear relation between NDVI and sealing degrees. First methodology tests show that newly derived 2009 sealing values are matching the 2006 sealing values to a high degree and that this procedure can be used for a sealing update, if sufficient care is applied to the definition of spatial and spectral thresholds for the sealing changes. Further on, these “sealing images” adapted to the 2006 NDVI calibration are derived for the total area of interest for both years and used as a basis for the change detection of both built-up surfaces as well as for deriving the sealing degrees within newly built-up areas.

The results of this geoland2 CMS EUROLAND activity shall serve as an essential input to support Europe-wide urban sprawl assessment for EEA and user DGs (i.e. DG REGIO, DG ENV and DG Agri) and to support Member States in upgrading their national data bases.