1. a Centre for Geo-Information, Wageningen University , PO Box 47, 6700, AA Wageningen, the Netherlands
2. b Department of Geo-information Processing , Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente , 7500, AA Enschede, the Netherlands
3. c Centre for Environmental Monitoring, National Institute for Public Health and the Environment (RIVM) , PO Box 1, 3720, BA Bilthoven, the Netherlands