First Achievements of the French National Land Data Centre
LEROY, Marc1; Kosuth, Pascal2; Hagolle, Olivier3; Cherchali, Selma1; Maurel, Pierre2; Desconnets, Jean-Christophe4

Nine French public institutions involved in Earth Observation, environmental studies and scientific research (CEA, CNES, Cirad, CNRS, IGN, INRA, IRD, Irstea and Météo-France), have recently launched a National Land Data Centre (NLDC), pooling their expertise and resources to make satellite data available to the environmental research community and to public policy actors. The NLDC primary mission is (i) to build a national space data infrastructure able to produce value-added space data over land and provide services fitted to users' needs, (ii) to support the sharing of experience and scientific knowledge on methodologies relevant to process and use space data for land thematic issues.

The overall objective of the French NLDC is to enhance scientific knowledge and support the development of management capacities in domains related with anthropogenic action and climate impact on ecosystems and territories, the observation, quantification and modelling of water and carbon cycles, the monitoring and modelling of changes in societies and their activities (urban planning, agriculture, forest management, ...), the understanding of biodiversity, its dynamics and related preservation strategies.

To this end, the NLDC is working to produce data, products, methods and services linked to space observations of continental areas, from local (ecosystem and territory) to global scale, and make them available to the user community. It is backed up by a distributed spatial data infrastructure, the Centre de Gestion et de Traitement des Données (CGTD), and by scientific expertise hubs in various regions. The CGTD links Montpellier (GEOSUD at Maison de la Télédétection) and Toulouse (CNES supported by the CESBIO laboratory, and IGN).

Products and services provided by the French NLDC are intended to be quality-controlled, to cover broad territories and long periods: annual satellite coverage of the national territory, high or very high resolution surface reflectance time series, bio-geophysical variables (biomass, water levels, surface humidity, etc) time series and products at global scale, visualization and data processing tools (Orfeo Tool Box), processing methods and algorithms, validation procedures, methodological guidelines and frameworks for thematic applications.

The activities of the NLDC are :

  • data acquisition : a program of satellite data acquisition over the national territory has started, mainly driven by GEOSUD in Montpellier. The program includes so far a yearly cover of the national territory at 5 m resolution with Spot, Rapid Eye and IRS data for the years 1997, 2005, 2009 to 2012, and will continue for the years to come. It also includes the very high resolution coverage of a number of cities and sensitive areas (rivers, coastal line, habitats...) with Pléiades data. The data are properly orthorectified in order to enable their superimposition over time. A specificity of the program is that the data can be made available free of charge to the whole national public sector. User workshops are organised to exchange information and feedback on user needs. Images will also be acquired over areas in southern countries in support to scientific partnerships.

  • data processing : a processing centre called MUSCATE has been developed in Toulouse. It is able to transform raw space data (level 0) in orthorectified surface reflectances (level 2), using an innovative atmosphere correction scheme based on physical principles able to produce from time series of raw data smooth temporal profiles of reflectances for each pixel. The processing line can process SPOT, Pléiades, Venµs, Formosat-2 data, and is designed to process also Sentinel-2 data. The target of the National Land Data Centre is to process Sentinel-2 and Landsat 8 data at level 2 (atmospheric corrections) and level 3 (monthly nearly cloud free composites) in a systematic way over France and other interest areas. MUSCATE has already started to process data from the SPOT 4 / Take 5 experiment designed to simulate the repetitiveness and coverage of Sentinel-2 data, as well as 2009 - 2011 Landsat data over France.

  • data distribution : a first version of a Web portal will be opened to the public in Spring 2013. It will include services of image discovery, visualisation and download. The first products to be displayed and put at the user community disposal will be those of current and former projects such as GEOSUD (yearly coverages of France), Postel (time series of biogeophysical variables at global scale) and Kalideos (time series of Spot images on selected sites). The product availability will gradually increase to include data from future GEOSUD yearly coverages and Pleiades acquisitions, from the Spot archive over France and large regions of the world, and from Sentinel-2 data.

    The data production of the National Land Data Centre are expected to generate large amounts of scientific results. First scientific results have already been released.

    A first exemple deals with the spatialized monitoring and quantification of nitrogen pollution pressures in western France to assess their impact on ground water quality. The November-December time period, with heavy rainfall and low vegetation cover is a critical period for nitrogen leaching. Installing interseasonal crops to ensure nitrogen fixation during the rainy autumn season is a major action contributing to the European Nitrogen Directive. NLDC data and products are used to quantify interseasonal crop density indicators, taking into account the dynamics of land use and agricultural practice. Results contribute to assess the impact of sound agricultural practice on water quality, to orientate public policies and to develop stakeholders awareness on the role and relevance of these practices.

    As a second example, a specific experiment (called Take 5) is currently under way to modify the SPOT 4 orbit so that the orbit repetitiveness is brought to 5 days, simulating the viewing conditions of Sentinel-2. SPOT 4 (Take5) images are acquired over 42 sites worldwide to allow future users to develop and test their methods on data sets similar to those of Sentinel-2. The sites are used to validate the atmospheric correction and cloud detection over a large variety of surfaces, to compare various Level 3 time compositing methods and to test several applications for which we will show during the conference the very first results (land cover and land use, agriculture, phenology, hydrology, snow monitoring, coasts monitoring, habitats characterisation and biodiversity...).

    The paper will present the foundations of the National Land Data Centre, its current development status, and will focus on first scientific results and relations with the ESA Sentinel-2 program.