[1] Faculty of Geo-information Science and Earth Observation (ITC), University of Twente, Enschede,7500AE, Netherlands
[2] Horticulture and Product Physiology, Wageningen University, PO Box 16, Wageningen,6700AA, Netherlands
[3] CNR-IREA, Institute for Electromagnetic Sensing of the Environment, National Research Council, Milan,20133, Italy