ENVISAT MERIS Data for Global Dryland Monitoring
Gangkofner, Ute1; Brockmann, Carsten2; Paganini, Marc3; Stoeger, Florence1; Danne, Olaf2; Wramner, Per4; Brito, José5; Fensholt, Rasmus6; Günther, Kurt7
1GeoVille, AUSTRIA; 2Brockmann Consult, GERMANY; 3ESA, ITALY; 4Brockmann Geomatics, SWEDEN; 5Cibio, PORTUGAL; 6University of Copenhagen, DENMARK; 7DLR, GERMANY
The presented "Drylands" part of the ESA Data User Element (DUE) Diversity II project exploits a decade of ENVISAT MERIS-FRS data for 22 globally distributed, large dryland sites (up to over 1 Mio km2). In setting up this project ESA aims at contributing with EO based methods to the strategic goals of the Convention on Biological Diversity (CBD), especially the supportive goal E: Enhance implementation through participatory planning, knowledge management and capacity building. Besides the CBD and other interested parties, also the UN Convention to Combat Desertification (UNCCD) is a major relevant and interested stakeholder and participating in the User Requirement compilations. The Diversity II project spans from 2012 to August 2014.
The specific aim of this project is to develop an EO-based monitoring scheme for assessment of status, changes and trends in biodiversity in global drylands using moderate resolution EO data. The primary products derived from the MERIS EO data and ancillary data are NPP (Net Primary Production) proxy parameters and RUE (Rain Use Efficiency) indices. These will be further processed and analysed in order to generate user–relevant, informative GIS products, showing the status, changes, and general trends of these variables through the last decade. While the NDVI (Normalised Difference Vegetation Index) is the most commonly used heritage NPP proxy index, Diversity II will focus on MERIS based Fraction of Absorbed Photosynthetically Active Radiation (FAPAR), and base the core degradation analyses and assessment on this index. To maintain continuity on the other hand, in addition a spectral band adjusted NDVI will be calculated with MERIS data and compared to global NDVI (GIMMS) data sets. The latter will serve to put the MERIS derived products in relation to the longer term (GIMMS available since 1981) trends and determine the vegetation status (i.e. the past trend) at the beginning of the MERIS lifetime.
A variety of ancillary data will be used, such as rainfall data, soil moisture, evapotranspiration, temperature, and land cover data, plus further data for GIS product generation. The status and trends will be determined both on a yearly basis, beginning with the local yearly wet season, and on a seasonal basis, i.e. for wet and dry season(s). Thus the yearly periods will vary all over the globe and yearly along with the wet season onset. This differentiated approach aims at accurately monitoring each rainy period and the subsequent dry period as one cycle, and at improving the RUE and other similar indices, e.g. based on soil moisture, by using seasonal integrals. By means of simple classification techniques and reasonable index combinations the indices will be transformed into indicators with defined thematic classes.
The resulting status, change and trend indicators will be spatially aggregated using e.g. administrative boundaries, land cover, aridity zones, protected areas, topography, and others. The aim is to establish a link to the potential drivers of biodiversity trends by analysing the behaviour of the NPP and RUE trends within these units. The underlying assumption is that there are relationships between NPP and RUE status and trends and the development of biodiversity. Using in addition ground data with in-situ measures of biodiversity, and relevant literature, the project aims at establishing such links. A "Biodiversity Story" per site will finally serve to highlight major developments at each site.