1. Centre for Remote Sensing and Land Surfaces; University of Bonn; Walter-Flex- Straße 3 D-53113 Bonn Germany
2. Institute of Crop Science and Resource Conservation; University of Bonn; Katzenburgweg 5 D-53115 Bonn Germany
3. Range Ecology and Range Management Group; Botanical Institute; University of Cologne; Zülpicher Straße 47b D-50674 Cologne Germany
4. Departamento de Métodos Cuantitativos y Sistemas de Información; Institute for Agricultural Plant Physiology and Ecology - IFEVA CONICET; Universidad de Buenos Aires; Av. San Martín 4453 C1417DSE Ciudad de Buenos Aires Argentina