SAR Displacement Mapping on Myanmar Earthquake Myint.M.M
Chief Scientist, Mapping and Natural Resources Informatics, Switzerland
maungmoe.myint[at]mnri.ch
Abstract
ABSTRACT
Mapping surface displacement at major cities and along the Sagaing fault is an important undertaking after 7.7 Magnitute Earthquake near Sagaing town and 6.7 Magnitude Earthquake near Mandalay town on 28 March 2025 in Myanmar. Surface displacement away from the satellite look direction causes an increase in the path (translating to phase) difference. The objective is to extract the displacement component from the different components of the observed phase using the Sentinel-1 Synthetic Aperture Radar (SAR) interferometric pair with small baseline while considering time baseline as small as possible to avoid decorrelation. Differential Interferometry DInSAR is applied to create an interferometric displacement map (expressed in meter) in line-of-sight (LOS) using a pair of Sentinel-1 SLC SAR co-polarized images of same sensor, geometry, incidence angle, data type, to show the land movement over time from the first pre-earthquake image to the second post-earthquake image. One fringe cycle in the interferogram corresponds to displacement relative to the SAR antenna only half of the wavelength. As the Sentinel-1 C band wavelength is 5.6 cm, one fringe cycle in this study corresponds to 2.8 cm of displacement. The methodology started with pre-earthquake and post-earthquake images in slant range geometry, applied precise orbit information, input the reference digital elevation model, highly accurate co-registration for correcting shift of between images up to 1000th of pixel, some range and azimuth corrections, computation and generation of raw interferogram, interferogram flattening for creating differential interferogram, interferogram filtering to reduce the phase noise for creating filtered interferogram and coherence, phase unwrapping to resolve the 2pi ambiguity to generate the absolute phase values, phase to displacement conversion for conversion of interferometric absolute phase to terrain displacement and geocoding to map projection. Each full cycle of differential phase corresponds to half of wavelength in SAR viewing direction. It is 2.5 cm in this study. Precision map and refined displacement map are also produced. This study successfully emphasises the displacement at Manadaly township where sinking is dominant, and also highlights the displacement at Sagaing township where uplift is dominant. It also signifies why the older Sagaing bridge structural damaged during the earthquake. Moreover, the study indicates the dominance of uplift of western side along the Sagaing fault. This study also answers why the Nay Pyi Taw town was damaged although it is 280 km south of earthquake epicenter. The quantitative uplift and sink values are also contributed.
