Yq Chen

Ground subsidence monitoring in Hong Kong with satellite SAR interferometry

Ground settlement has long been a problem in Hong Kong, as most usable land in Hong Kong was reclaimed from the sea. Ground settlement may affect building structures and underground facilities such as water supply and sewage systems built on the land. Measurements of ground settlement can provide valuable data for assessing the impacts of ground settlement and for improving designs of future land reclamation projects. Experiments have been carried out to assess the performance of INSAR in the environment of Hong Kong especially the temporal decorrelations of SAR images and the potential atmospheric effects on INSAR measurements, and to use INSAR to study the ground settlement problem in Hong Kong. This study finds that the temporal decorrelation is an important problem in the heavily vegetated rugged areas as usually expected, and that the atmospheric effects can be very significant at times. Ground settlements measured over the airport and a residential area are presented. It can be seen from the results that both of the areas are still settling significantly many years after the reclamation.

Pre- and co-seismic ground deformations of the 1999 Chi-Chi, Taiwan earthquake, measured with SAR interferometry

The 1999 M-w = 7.6 Chi-Chi earthquake was the strongest inland earthquake in Taiwan in the 20th century. Five radar images acquired with the C-band SARs onboard the ERS-1/2 satellites are combined to study the pre- and co-seismic surface deformations in the epicentral area of about 1500 km(2). The pre-seismic interferograms over 2-3 years show consistent fringe patterns that are equivalent to LOS displacement variations of up to about 32 mm. The deformations are likely caused by the east-west tectonic compression in the region. The short-term co-seismic interferograms show clear arc-shaped fringe patterns of about 10 fringes, equivalent to displacement variations of about 28.3 cm. The co-seismic deformation results fit well with both GPS measurements and a simulated interferogram computed based on a fault-dislocation model. This study demonstrates the capability of short-wavelength InSAR systems for monitoring ground deformations of flat terrain in tropical regions

Assessing consistency of Chang’E-1 and SELENE reference frames using nearly-colocated laser altimetry footprint positions

The consistency of the Chang’E-1 and SELENE reference frames as realized by the footprint positions of laser altimetry measurements of the lunar surface during both missions was analyzed using a global 12-parameter model for small (with respect to unity) deformations and rigid body motions. The rigid body motion and deformation parameters between the two reference frames estimated from nearly-colocated without tie measurements are found to be consistent, i.e., nearly zero for the estimates of the translations, rotations and shear parameters. However, the estimated three strain parameters, which are similar in magnitude and sign, reveal a prominent scale difference, between the Chang’E-1 and SELENE reference frames, of about 0.9 × 10−5. The scale difference can be attributed to calibration of the data sets using the known coordinates of the lunar laser ranging stations all located on the near side of the Moon.