Acknowledgments
The authors declare that they have no known competing interest that could have appeared to influence the work presented in this paper. This work was supported by the Hong Kong Research Grants Council [grant numbers CUHK14303417, CUHK14303119, and HKPFS PF16-03859]; the National Natural Science Foundations of China [grant number 41690142 and 42071410]; the CUHK Direct Grant for Research [grant number 4053282 and 4053426]; and the CAS ”Light of West China” Program. The ALOS-1 PALSAR data are copyrighted and provided by the Japan Aerospace Exploration Agency through the EO-RA2 project ER2A2N081. The TanDEM-X DEM data are copyrighted and provided by the German Aerospace Centre through project DEM_GLAC1408.