| dc.description.abstract | Recently, with the launch of new Synthetic Aperture Radar (SAR) missions, Interferometric Synthetic Aperture Radar (InSAR) has become more and more useful tool for researchers. The developments of SAR techniques have gone far beyond the original scope, covering different disciplines. SAR imagery is now used for biomass mapping, glacier tracking, landcover classification and especially monitoring the deformation of the Earth’s surface.
SAR could be used for monitoring the stability of ancient monuments, historical buildings and archaeological sectors. Compared to traditional monitoring techniques, the use of radar remote sensing for monitoring cultural heritage sites has both advantages and disadvantages. In the positive manners, those sites could be automatically monitored regardless day/night time and weather conditions. More comprehensive pictures could be potentially derived, and damages to structures could be possibly minimized or avoided. The major limitations, on the other hand, lay on the resolution of SAR imagery and SAR processing techniques. Most of current SAR sensors are not appropriate for monitoring surface displacements at a very small scale and high precision, and SAR processing techniques primarily optimize for large deformation patterns.
In this work, the X-band TerraSAR-X imagery is used for the sake of resolution and precision. To enhance the monitoring coverage and detail, we integrated the oversampling techniques to the Small Baseline (SB) InSAR for processing SAR imagery. Test site was choosen at the Historical Centre of Hanoi, Vietnam, where the relics were left by most Vietnamese dynasties in the past, greater than any other places over the country.
A total of 6.29 million radar targets were obtained, maintaining the average density of 217,012 points/km2. Our results suggest that image oversampling not only increased the number of measurement points 4.4 times more than the standard processing chain, but also removed the noisiest points. The observed subsidence patterns are mostly related to adjacent groundwater extraction and construction activities, with maximum subsiding rate reached −18.1 mm/year for the study period from April 2012 to November 2013. Generally, heritage assets and monuments in the Citadel, the Old Quarter and French Quarter remain in a steady state, whereas those located along the Red River and in southern Hanoi were subjected to subsidence. | en_US |