Subsidence rate monitoring of Aghajari oil field based on Differential SAR Interferometry

Land subsidence, due to natural or anthropogenic processes, causes significant costs in both economic and structural aspects. That part of subsidence observed most is the result of human activities, which relates to underground exploitation. Since the gradual surface deformation is a consequence of hydrocarbon reservoirs extraction, the process of displacement monitoring is amongst the petroleum industry priorities. Nowadays, Differential SAR Interferometry, in which satellite images are utilized for elevation change detection and analysis – in a millimetre scale, has proved to be a more real-time and cost-effective technology in contrast to the traditional surveying method. In this study, surface displacements in Aghajari oil field, i.e. one of the most industrious Iranian hydrocarbon sites, are being examined using radar observations. As in a number of interferograms, the production wells inspection reveals that surface deformation signals develop likely due to extraction in a period of several months. In other words, different subsidence or uplift rates and deformation styles occur locally depending on the geological conditions and excavation rates in place.     

Physical assessment of coastal vulnerability under enhanced land subsidence in Semarang,Indonesia, using multi-sensor satellite data

Research has been conducted in Semarang, Indonesia, to assess coastal vulnerability under enhanced land subsidence using multi-sensor satellite data, including the Advanced Land Observing Satellite (ALOS) Phased Array type L-band SAR (PALSAR), Landsat TM, IKONOS, and TOPEX/Poseidon. A coastal vulnerability index (CVI) was constructed to estimate the level of vulnerability of a coastline approximately 48.68?km in length using seven physical variables, namely, land subsidence, relative sea level change, coastal geomorphology, coastal slope, shoreline change, mean tidal range, and significant wave height. A comparison was also performed between a CVI calculated using seven parameters and a CVI using six parameters, the latter of which excludes the land subsidence parameter, to determine the effects of land subsidence during the coastal vulnerability assessment. This study showed that the accuracy of coastal vulnerability was increased 40% by adding the land subsidence factor (i.e., CVI 6 parameters?=?53%, CVI 7 parameters?=?93%). Moreover, Kappa coefficient indicated very good agreement (0.90) for CVI 7 parameters and fair agreement (0.3) for CVI 6 parameters. The results indicate that the area of very high vulnerability increased by 7% when land subsidence was added. Hence, using the CVI calculation including land subsidence parameters, the very high vulnerability area is determined to be 20% of the total coastline or 9.7?km of the total 48.7?km of coastline. This study proved that land subsidence has significant influence on coastal vulnerability in Semarang.     

GPS monitoring of vertical seafloor motion at Platform Harvest

We describe results from two decades of monitoring vertical seafloor motion at the Harvest oil platform, NASA’s prime verification site for the TOPEX/Poseidon and Jason series of reference altimeter missions. Using continuous GPS observations, we refine estimates of the platform subsidence—due most likely to fluid withdrawal linked to oil production—and describe the impact on estimates of stability for the altimeter measurement systems. The cumulative seafloor subsidence over 20 yrs is approximately 10 cm, but the rate does not appear constant. The apparent non-linear nature of the vertical motion, coupled with long-period GPS errors, implies that the quality of the seafloor motion estimates is not uniform over the 20-yr period. For the Jason-1 era (2002–2009), competing estimates for the subsidence show agreement to better than 1 mm yr⁻¹. Longer durations of data are needed before the seafloor motion estimates for the Jason-2 era (2008–present) can approach this level of accuracy.     

运输机短舱挂架纵向位置优选数值研究

针对运输机的翼/身/架/舱干扰问题,本文基于Euler方程,采用笛卡尔直角网格,应用有限体积法对全机绕流流场进行数值计算,分析和比较了短舱挂架不同前伸量、下沉量的影响,提出了基于最佳前伸量和下沉量的优选配合位置,并与初始位置的全机气动特性进行对比。结果表明,获得的短舱挂架优选配合位置使全机气动特性得到了明显改善和提高。     

Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang,Indonesia by SBAS DInSAR analyses using Envisat-ASAR,ALOS-PALSAR,and Sentinel-1A SAR data

Land subsidence is a critical issue that large cities located in coastal areas, such as Semarang, Indonesia, must address. The monitoring of land subsidence is vital for predicting and mitigating the disasters that such subsidence may cause. Therefore, an economical and effective monitoring method, which can continuously provide accurate measurements over extensive areas, is highly required. Differential Interferometry Synthetic Aperture Radar (DInSAR) has the potential to be a powerful technique that can meet the above demands. Actually, DInSAR has been applied to monitor the subsidence in Semarang, but it was for a limited period before 2012.In order to clarify the transition of the long-term subsidence behavior in Semarang, the Small Baseline Subset (SBAS) method, which is one type of time-series DInSAR, is employed in this research. The sets of data of Envisat-ASAR (2003–2007), ALOS-PALSAR (2007–2011), and Sentinel-1A (2015–2017) are employed for the analyses. Then, the validity of the SBAS results is discussed from the viewpoints of both spatial distribution and temporal transition using GPS displacement measurement results and the geological conditions of the ground.On the other hand, as the lifespan of SAR satellites is commonly designed to be around 5–7?years, an appropriate method, which can connect the subsidence provided independently by the unlinked time-series data sets of the three different SAR satellite data, is required. This study uses the Hyperbolic Method (HM) to connect the above unlinked SBAS results. The HM is often used to fit the monitored subsidence in practice as a geotechnical engineering tool. Using this method, 14?years of the temporal behavior of the subsidence in Semarang is evaluated.It is found that the transition of the subsidence is different depending on the location, and that the subsidence rate is still increasing in the north and northeast parts of the coastal area. This study shows that SBAS DInSAR can be a useful tool for long-term continuous subsidence monitoring.     

基于永久散射体合成孔径雷达干涉测量技术的地面沉降监测

城市施工建设及地下水开采活动日益频繁，导致城市地面沉降问题日益严重。虽然传统地面沉降监测技术的精度较高，但成本也高。近年来，星载合成孔径雷达干涉测量(InSAR)技术发展起来，已被用于监测大范围地表形变，具有低成本、大面积、高精度等特点。首次采用永久散射体合成孔径雷达干涉测量(PSInSAR)技术，监测上海西南某区域2017—2021年间的地面沉降。结果显示:除一处楼房外，该区域大部分地区未发生沉降，最大沉降速率约-7.10 mm/a，最大沉降量约25.43 mm。采用该技术监测沉降，一方面节省了大量的人力和物力;另一方面，本研究成果对城市地表沉降的科学防治具有重要的参考意义。