1. C-CORE and Department of Electrical Engineering, Memorial University of Newfoundland, St John's, NL A1B 3X5, Canada;
2. The Canada Center for Mapping and Earth Observation, Ottawa, ON K1S 5K2, Canada;
3. Department of Geodesy, Section of Remote Sensing, GFZ German Research Center for Geosciences, Potsdam, Germany;
4. Institute of Photogrammetry and GeoInformation, Leibniz University Hannover, 30167 Hannover, Germany