Description: Remote sensing of night light emissions in the visible band offers a unique opportunity to directly observe human activity from space. This has allowed a host of applications including mapping urban areas, estimating population and GDP, monitoring disasters and conflicts. More recently, remotely sensed night lights data have found use in understanding the environmental impacts of light emissions (light pollution), including their impacts on human health. In this review, we outline the historical development of night-time optical sensors up to the current state of the art sensors, highlight various applications of night light data, discuss the special challenges associated with remote sensing of night lights with a focus on the limitations of current sensors, and provide an outlook for the future of remote sensing of night lights. While the paper mainly focuses on space borne remote sensing, ground based sensing of night-time brightness for studies on astronomical and ecological light pollution, as well as for calibration and validation of space borne data, are also discussed. Although the development of night light sensors lags behind day-time sensors, we demonstrate that the field is in a stage of rapid development. The worldwide transition to LED lights poses a particular challenge for remote sensing of night lights, and strongly highlights the need for a new generation of space borne night lights instruments. This work shows that future sensors are needed to monitor temporal changes during the night (for example from a geostationary platform or constellation of satellites), and to better understand the angular patterns of light emission (roughly analogous to the BRDF in daylight sensing). Perhaps most importantly, we make the case that higher spatial resolution and multispectral sensors covering the range from blue to NIR are needed to more effectively identify lighting technologies, map urban functions, and monitor energy use.

Description: The oil expulsion efficiency of organic-rich shale during peak oil generation influences the generation of shale gas at high maturity, while the gas expulsion and loss efficiency affect the enrichment and preservation of shale gas. Two series of semiclosed hydrous pyrolysis experiments were performed under in situ geological conditions on Devonian shale sample as comparable analogue to evaluate the generation and preservation potential of shale gas in the Wufeng-Longmaxi Formation shale in the southeastern Sichuan Basin. The results indicate that the maximum oil expulsion efficiency of the Wufeng-Longmaxi shale is 68.8%. Retained oil is the main source of shale gas formed at high maturity. When the value of equal vitrinite reflectance (EqVRo) reaches 3.18%, the total gas generative potential from the retained oil and kerogen is 214.06 mL/g TOC, while that from kerogen is only 69.84 mL/g TOC. Overall, retained oil-formed gas at high maturity (EqVRo 〉1.30%) accounts for 60.82%–68.26% of the total gas, and the kerogen-formed gas is between 31.74% and 39.18% of the total gas. Based on the analysis of the JY2 well, Wufeng-Longmaxi shales with TOC contents 〉1.5% lose 60–80% of the total gas, while shales with TOC contents 〈1.5% lose 70–100% of the total gas. A TOC content of 1.5% can still meet the 2 m3/t gas content as evaluation standard for selecting favorable marine shale gas play areas in China.

Description: This study aims to characterize the geological properties and to evaluate the gas potential of the lower Paleozoic shales in the Yichang area by integrating a series of analyses on geology and geochemistry, well logging data, and 2D seismic interpretation. The thickness of the lower Cambrian Shuijingtuo shale is less than 10 m in the southeast but may exceed 120 m in the southwest area. The thickness of the upper Ordovician Wufeng shale and the lower Silurian Longmaxi shale (hereafter referred to as the Wufeng-Longmaxi shale) gradually increases in thickness from 〈10 m in the south to 40–50 m in the northeast. The organic matter of the above two sets of black shale is mainly dominated by type I and II1 kerogen. The thickness of black shale units with TOC 〉 2% is more than 10–20 m, commonly located at the bottom of the shale intervals. Black shales near the Huangling anticline have low thermal maturity due to its relatively shallow burial. The predominant minerals are quartz and clay minerals. Carbonate contents of the Shuijingtuo shale are relatively high compared to the Wufeng-Longmaxi shale. Pores are more developed in the Wufeng-Longmaxi shale than those in the Shuijingtuo shale. Natural fractures are common in the Shuijingtuo shale but are rare in the Wufeng-Longmaxi shale. The well logging and lab analytical results both indicate that the natural gas content in the black shales is relatively high. The prospective area of the Shuijingtuo interval for shale gas production is nearly 670 km2, located in the southwestern region. In contrast, the prospective area of the Wufeng-Longmaxi interval for shale gas production is approximately 1590 km2, situated in the eastern area.

Description: A gravity sensor onboard an aircraft always measures the sum of all accelerations acting on the sensor. To separate the accelerations caused by the movement of the aircraft from the gravitational accelerations, the movement, including position, velocity, and acceleration of the aircraft, must be measured independently. Nowadays, this is possible using GNSS. Obviously, this means that the kinematic acceleration must be measured or derived from GNSS measurements as accurately as the gravity survey. Compared to the traditional airborne gravimetry, the determination of positions and velocities from GNSS is a big challenge for the special HALO aircraft, which is characterized by high-altitude and long-range flying capability. A strategy of integrated GNSS Doppler velocity determination based on a combination of robust estimation and Helmert variance components estimation (VCE) is proposed in this study to fulfill the requirements for this aircraft. This strategy is tested by processing GNSS Doppler data recorded onboard the HALO aircraft. The velocity obtained has been applied in the data processing of the GEOHALO airborne gravimetry campaign of 2012. The results show that the proposed strategy improves GNSS Doppler velocity determination accuracy and allows the subtraction of the kinematic vertical accelerations from the GEOHALO airborne gravimetry records.

Description: Monitoring ground displacement produced by underground mining is essential to ensure the safety of infrastructure over mining areas. Differential synthetic aperture radar (DInSAR) can only obtain the one-dimensional (1D, i.e., along the line-of-sight (LOS) direction) displacement component. In this study, we present an improved algorithm for retrieving and predicting three-dimensional (3D) displacement fields induced by underground mining based on the LOS displacement derived from DInSAR and the probability integral method (PIM). Whole parameters included in the standard PIM model are involved in the improved algorithm. In addition, the interaction between multiple working panels is considered and incorporated into the model. Next, a stochastic optimization technique hybridizing the cultural algorithm and random particle swarm optimization (CA-rPSO) has been designed to retrieve model parameters, which can be used to retrieve and predict the 3D displacement field. Simulated experiments show that the RMSEs are 10 mm, 12 mm and 17 mm in the vertical, east-west and north-south directions, respectively, by comparing the simulated and retrieved 3D displacement. Furthermore, the capability of the proposed method is investigated and validated in the Xuehu mining area of China using three ALOS PALSAR acquisitions. Our results agree well with levelling measurements in the vertical direction with a RMSE of 38 mm. Although the retrieved horizontal displacement cannot be validated due to a lack of field surveys, these displacement fields coincide spatially with the evolution of mining excavation.

Description: Hydrogen induced plasticity has been found in metallic glasses; however, the underlying mechanism remains unclear. Herein, we studied a Cu-Zr metallic glass charged in a hydrogen atmosphere inside an environmental transmission electron microscope. Compression tests of hydrogen charged nanopillars show more controllable deformation compared to uncharged ones. A variable resolution fluctuation electron microscopy study of the hydrogen charged samples reveals an increase in the correlation length of the medium-range order. Our results provide experimental evidence for hydrogen-induced heterogeneity and support the idea that increasing the degree of heterogeneity leads to multiple local shear events and suppresses catastrophic shear banding.

Description: The symmetry of conjugate rifted margins is a first-order observable feature reflecting the geodynamic processes acting during and after continental rifting. The symmetry of the South China Sea (SCS) rifted margins can be deduced from comprehensive geophysical datasets on a continental-margin scale. Here, we combine three key approaches: (1) lateral fault distributions are delineated according to free-air gravity anomalies, (2) crustal stretching styles are mapped based on gravity inversion constrained by deep seismic profiles, and (3) total extension of conjugate margins is estimated according to margin restorations and tectonic settings. We infer a predominantly symmetric rifting style caused by pure shear extension, with only narrow domains of asymmetric deformation in continent-ocean transition (COT) regions that have undergone simple shear and where the lower crust of the highly thinned distal margin is embrittled before continental breakup. However, our analysis also suggests that this symmetry has been modified by post-rift geodynamic processes. Southward lower crustal flow, which occurred only on the southern margin due to the low viscosity of the lower crust and the slab pull induced by the subducting Proto-SCS plate during seafloor spreading, shifted the crustal stretching styles from symmetric to asymmetric. The collision between the southern margin and Borneo thickened the lower crust more than the upper crust at the southern end of the southern margin and shortened the southern margin. This event had a large impact on the SE margin but a small impact on the SW margin. We conclude that (1) for the SE and NE margins, the crustal stretching styles shifted from asymmetric to approximately symmetric, and the total extension shifted from symmetric to asymmetric; (2) for the SW and NW margins, the crustal stretching and total extension remained asymmetric and symmetric, respectively.