Ground subsidence in Mekong delta, Vietnam (2018-10-26)

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Activation date: 2018-10-26 <br>
Event type: Other <br>
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Activation reason: <br>
The EMSN057 service provides geospatial information facilitating assessment of drivers of ground subsidence and to supporting analysis of the relation between detected ground subsidence and land use changes in Ca Mau, Long Xuyen and Rach Gia areas in the Mekong delta, Vietnam. The primary objective of the service is provision of spatially and temporally consistent, dense and synoptic results giving insight on the distribution and variance of subsidence phenomena in space and its dynamics in time. The persistent scatterers interferometry (PSI) technique, measuring ground deformations from stacks of archive SAR imagery (Sentinel-1 and TerraSAR-X), was utilized to estimate displacements. Products should complement ground based measurements, information from previous InSAR studies and contribute to evidence-based risk assessment.Annual Ground Subsidence Displacement The raster product, with 10 x 10m resolution, shows annual ground subsidence displacements in the vertical direction. The product was interpolated from displacement values of persistent scatterer points detected by the PSI technique from a stack of archived satellite SAR images.Annual Ground Subsidence Displacement ChangeThe change product shows differences of annual ground subsidence displacements in the vertical direction. It was obtained by deduction of previous from subsequent annual versions of Displacement products.In addition, average annual subsidence displacement velocity and displacement trend were evaluated from the PSI results, as demonstrated below.  <br>
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启用日期：2018-10-26
事件类型：其他

启用缘由：
EMSN057服务提供地理空间信息，可辅助评估地面沉降的驱动因子，并支持分析越南湄公河三角洲金瓯（Ca Mau）、龙川（Long Xuyen）及沥架（Rach Gia）区域内，已探测到的地面沉降与土地利用变化之间的关联。本服务的核心目标是产出空间与时间上一致性强、覆盖密集且全域同步的成果，以揭示地面沉降现象的空间分布、差异特征及其时间动态变化。本研究采用永久散射体干涉测量（Persistent Scatterers Interferometry, PSI）技术，通过堆叠存档合成孔径雷达（Synthetic Aperture Radar, SAR）影像（Sentinel-1与TerraSAR-X）测算地面形变，进而估算位移量。相关产品可补充地面实测数据、过往干涉合成孔径雷达（Interferometric Synthetic Aperture Radar, InSAR）研究的信息，并为循证风险评估提供支撑。

年度地面沉降位移
该栅格产品分辨率为10×10米，展示垂直方向的年度地面沉降位移量。该产品由PSI技术从存档卫星SAR影像堆栈中探测到的永久散射体点的位移值插值生成。

年度地面沉降位移变化量
该变化产品展示垂直方向年度地面沉降位移的差值，通过将后续年度的位移产品与前期年度版本相减得到。

此外，研究还从PSI结果中评估了年均沉降位移速率与位移趋势，如下文所述。