1. a European Commission , Joint Research Centre , Institute for the Protection and Security of the Citizen , Sensors , Radar Technologies and Cybersecurity Unit , Via Fermi 2749, T.P. 670 ‐ Ispra (VA), 21027, Italy
2. b Laboratory of Remote Sensing , School of Rural and Surveying Engineering , National Technical University of Athens , Heroon Polytechniou 9, Zographos, 15780, Greece
3. c Hellenic Centre for Marine Research , P.O. Box 712, 19013 Anavissos, Greece