Ground instability detection using PS-InSAR in Lanzhou, China

This paper reports on the application of radar satellite data and Persistent Scatterer Interferometry (PS-InSAR) techniques for the detection of ground deformation in the semi-arid loess region of Lanzhou, northwestern China. Compared with Synthetic Aperture Radar Interferometry (InSAR), PS-InSAR overcomes the problems of temporal and geometric de-correlation and atmospheric heterogeneities by identifying persistent radar targets (PS) in a series of interferograms. The SPINUA algorithm was used to process 40 ENVISAT ASAR images for the study period 2003–2010. The analysis resulted in the identification of over 140000 PS in the greater Lanzhou area covering some 300 km2. The spatial distribution of moving radar targets was checked during a field campaign and highlights the range of ground instability problems that the Lanzhou area faces as urban expansion continues to accelerate. The PS-InSAR application detected ground deformations with rates up to 10 mm a−1; it resulted in the detection of previously unknown unstable slopes and two areas of subsidence. Lanzhou is the capital of Gansu Province and is one of the most important industrial cities in NW China (Fig. 1). The 12th Five-Year Plan and the 2011 National Economic and Social Development Statistical Bulletin of Lanzhou City indicate that the gross domestic product (GDP) of Lanzhou more than doubled in the last decade, reaching some 136 billion Yuan (c. £13.6 billion). This is associated with a rapid increase in the urban population and current forecasts suggest that the remaining undeveloped land can sustain further development for only some 10–15 years (Yao 2008). Increasingly, people have to encroach on marginal areas having a greater potential for ground instability. Since 1949, a variety of geohazards (mainly comprising landslides, debris flows, soil collapse, subsidence and floods) in Lanzhou have caused some 676 deaths and an estimated cumulative direct economic loss of some 756 million Yuan (Ding & Li 2009; Dijkstra et al. 2014). It is expected that further casualties and economic impacts will result in this unstable landscape unless a better understanding of the spatial distribution and causes of typical geohazards involving ground instability can be implemented in the development of land-use management practices, urban planning and the design of mitigation strategies. Satellite-based radar interferometry provides an opportunity to map ground deformation over large areas of interest. This paper highlights the use of PS-InSAR (Permanent Scatterer Synthetic Aperture Radar Interferometry) in a region where an incomplete ground instability inventory exist

Full-Scale System for Quantifying Loads and Leak Rates of Seals for Space Applications

NASA is developing advanced space-rated vacuum seals in support of future space exploration missions to low-Earth orbit and other destinations. These seals may be 50 to 60 in. (127 to 152 cm) in diameter and must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions to the International Space Station or the Moon. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them during docking or mating, and seal adhesion forces must be low to allow two mated systems to separate when required. NASA Glenn Research Center has developed a new test apparatus to measure leak rates and compression and adhesion loads of candidate full-scale seals under simulated thermal, vacuum, and engagement conditions. Tests can be performed in seal-on-seal or seal-on-flange configurations at temperatures from -76 to 140 F (-60 to 60 C) under operational pressure gradients. Nominal and off-nominal mating conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features of the test apparatus as well as techniques used to overcome some of the design challenges

AUTSEG: Automatic Test Set Generator for Embedded Reactive Systems

Part 2: Tools and FrameworksInternational audienceOne of the biggest challenges in hardware and software design is to ensure that a system is error-free. Small errors in reactive embedded systems can have disastrous and costly consequences for a project. Preventing such errors by identifying the most probable cases of erratic system behavior is quite challenging. In this paper, we introduce an automatic test set generator called AUTSEG. Its input is a generic model of the target system, generated using the synchronous approach. Our tool finds the optimal preconditions for restricting the state space of the model. It only works locally on significant subspaces. Our approach exhibits a simpler and efficient quasi-flattening algorithm than existing techniques and a useful compiled form to check security properties and reduce the combinatorial explosion problem of state space. To illustrate our approach, AUTSEG was applied to the case of a transportation contactless card

Full-Scale System for Quantifying Leakage of Docking System Seals for Space Applications

NASA is developing a new docking and berthing system to support future space exploration missions to low-Earth orbit, the Moon, and Mars. This mechanism, called the Low Impact Docking System, is designed to connect pressurized space vehicles and structures. NASA Glenn Research Center is playing a key role in developing advanced technology for the main interface seal for this new docking system. The baseline system is designed to have a fully androgynous mating interface, thereby requiring a seal-on-seal configuration when two systems mate. These seals will be approximately 147 cm (58 in.) in diameter. NASA Glenn has designed and fabricated a new test fixture which will be used to evaluate the leakage of candidate full-scale seals under simulated thermal, vacuum, and engagement conditions. This includes testing under seal-on-seal or seal-on-plate configurations, temperatures from -50 to 50 C (-58 to 122 F), operational and pre-flight checkout pressure gradients, and vehicle misalignment (plus or minus 0.381 cm (0.150 in.)) and gapping (up to 0.10 cm (0.040 in.)) conditions. This paper describes the main design features of the test rig and techniques used to overcome some of the design challenges

Automated reasoning on feature models

Software Product Line (SPL) Engineering has proved to be an effective method for software production. However, in the SPL community it is well recognized that variability in SPLs is increasing by the thousands. Hence, an automatic support is needed to deal with variability in SPL. Most of the current proposals for automatic reasoning on SPL are not devised to cope with extra– functional features. In this paper we introduce a proposal to model and reason on an SPL using constraint programming. We take into account functional and extra–functional features, improve current proposals and present a running, yet feasible implementation

Data-efficient performance learning for configurable systems

Many software systems today are configurable, offering customization of functionality by feature selection. Understanding how performance varies in terms of feature selection is key for selecting appropriate configurations that meet a set of given requirements. Due to a huge configuration space and the possibly high cost of performance measurement, it is usually not feasible to explore the entire configuration space of a configurable system exhaustively. It is thus a major challenge to accurately predict performance based on a small sample of measured system variants. To address this challenge, we propose a data-efficient learning approach, called DECART, that combines several techniques of machine learning and statistics for performance prediction of configurable systems. DECART builds, validates, and determines a prediction model based on an available sample of measured system variants. Empirical results on 10 real-world configurable systems demonstrate the effectiveness and practicality of DECART. In particular, DECART achieves a prediction accuracy of 90% or higher based on a small sample, whose size is linear in the number of features. In addition, we propose a sample quality metric and introduce a quantitative analysis of the quality of a sample for performance prediction

Introduction to geohazards of Central China

This thematic set of papers is intended to raise awareness of the types, nature, effects and impacts of geohazards in Central China. The papers will be published in this and subsequent issues of QJEGH and demonstrate the significant impacts that are wrought on the lives and livelihoods of those who live and work in the mountainous areas of Central China. China is all too often in the news as a result of geohazards that have a severe impact on lives and livelihoods. The mountainous terrain of Central China is subject to frequent hazards of high intensity with recent examples such as the 2008 Wenchuan earthquake and the 2010 Zhouqu debris flow. Rapid economic development brings with it expansion of urban centres and infrastructure networks, which not only increases the exposure of the population to natural processes in a dynamic environment, but can also lead to further strains on a landscape that is only marginally stable. Frequent geohazard events have sparked much research in an effort to better understand processes and material properties that can be used to inform and implement effective strategies to mitigate against the negative consequences of these geohazards