Feifei Qu

Pre-2014 mudslides at Oso revealed by InSAR and multi-source DEM analysis

The March 22, 2014 Oso mudslide at Washington was an extreme event costing nearly 40 deaths and damaging civilian properties. Historic record indicates that there have been serial events in decades. In our study, the combination of multi-source digital elevation models (DEMs), interferometric synthetic aperture radar (InSAR), and time-series InSAR analysis allowed us to characterize the Oso mudslide. The difference of shuttle radar topography mission (SRTM) and 2003 light detection and ranging (LiDAR) DEM indicated the topographic changes before 2006 mudslide, and the combination of time-series InSAR analysis and old-dated DEM (2000 SRTM, 2003 LiDAR DEM) revealed topographic changes associated with the 2006 sliding event. InSAR results from advanced land observing satellite (ALOS) phased array type L-band synthetic aperture radar (PALSAR) and LiDAR DEMs show that there were no significant topographic changes between 2007 and 2013 before the 2014 mudslide. The lasting toe erosion and logging near the landslide site could affect the 2006 mudslide event. Elevated discharges during wet seasons after 2006 accelerated the erosion of slumps deposited after the 2006 mudslide, which lessened the beneficial buttressing effect of the landslide toe with increased pore pressure during relatively higher rainfall after 2006. The vicious toe erosion within a relatively short period of eight years might play a critical role on the run-away event at Oso in 2014.

Post-Eruptive Inflation of Okmok Volcano, Alaska, from InSAR, 2008–2014

Okmok, a ~10-km wide caldera that occupies most of the northeastern end of Umnak Island, is one of the most active volcanoes in the Aleutian arc. The most recent eruption at Okmok during July–August 2008 was by far its largest and most explosive since at least the early 19th century. We investigate post-eruptive magma supply and storage at the volcano during 2008–2014 by analyzing all available synthetic aperture radar (SAR) images of Okmok acquired during that time period using the multi-temporal InSAR technique. Data from the C-band Envisat and X-band TerraSAR-X satellites indicate that Okmok started inflating very soon after the end of 2008 eruption at a time-variable rate of 48–130 mm/y, consistent with GPS measurements. The “model-assisted” phase unwrapping method is applied to improve the phase unwrapping operation for long temporal baseline pairs. The InSAR time-series is used as input for deformation source modeling, which suggests magma accumulating at variable rates in a shallow storage zone at ~3.9 km below sea level beneath the summit caldera, consistent with previous studies. The modeled volume accumulation in the six years following the 2008 eruption is ~75% of the 1997 eruption volume and ~25% of the 2008 eruption volume.

Large coverage surface deformation monitoring with multiple insar techniques and multiple sensor SAR datasets: a case study in Linfen-Yuncheng basin, China

The Linfen-Yuncheng Basin (LYB) is one of the most serious geo-hazards regions in China, which have been experiencing severe geo-tectonic movement, seismic, land subsidence and ground fissures. To monitor the complex surface deformation at LYB, Interferometric Synthetic Aperture Radar (InSAR) is employed. Forty-nine scenes acquired from three SAR tracks from 2007 to 2011 are used to obtain the ground deformation over LYB based on four multi-temporal InSAR analysis methods (i.e. PI-RATE, Stacking, SBAS and TCP). The maximum displacement is observed in Jishan County with the subsidence rate up to 120 mm/yr in the vertical direction. Two visually triangular areas are recognized at Jishan and Taocun-Xiaxian, which are controlled by local normal faults. In addition, cross-validation of the results in overlapping areas between adjacent tracks, ascending and descending tracks are conducted, which show good consistency among four methods.

Simultaneous estimation of building height and ground deformation over Xi'an City, China using multi-temporal InSAR method

InSAR has been widely used in monitoring land subsidence over large area. However, many factors in InSAR processing, such as decorrelation error, atmosphere error, height error and thermal noise limit the accuracy of InSAR measurements. The height error over urban area is particularly the most difficult issue in TerraSAR-X data processing for its shorter wavelength and higher spatial resolution. We employed a Multi-temporal InSAR (MTI) method based on the PS and SBAS method proposed by Hopper to estimate height of urban building and ground deformation simultaneously. By means of MTI method, the first raw urban DSM with 1,500 km2 areas over urban area has been mapped with a height accuracy of about 5 m. The MTI-derived deformation shows that the established TerraSAR DSM reduced the height error influence on deformation phase effectively. GPS and leveling measurements are applied to calibrate the InSAR results. Precision of our InSAR annual subsidence can reach 6 mm.

Surface deformation analysis of Xian (China) in 2009 carried out with refined SBAS-DInSAR

Taking the land subsidence and ground fissure in Xian as the research object and nine Envisat ASAR images spanning the whole year of 2009 as the data source, time series surface deformation of Xian city from January to December in 2009 are obtained by SBAS-DInSAR approach, where the baselines and topographic phase were refined using ground control points (GCP). The results show that Xian is the state of continuous subsidence in 2009 and subsidence funnels are shaped nearly in oval whose long axis direction was approximately parallel to ground fissure direction. Meanwhile, the regional and seasonal characteristics were displayed for these subsidences regional. In addition, spatial distribution of strong activities and active regulation within the year between ground fissures and land subsidence are uniform based on this investigation.