The No.4 tailings pond of the Dexing Copper Mine is the second largest in Asia. The tailing pond is a dangerous source of man-made debris flow with high potential energy. In view of the lack of effective and low-cost global safety monitoring means in this region, in this paper, the time-series InSAR technology is innovatively introduced to monitor the deformation of tailings dam and significant key findings are obtained. First, the surface deformation information of the tailings pond and its surrounding areas was extracted by using SBAS-InSAR technology and Sentinel-1A data. Second, the cause of deformation is explored by analyzing the deformation rate, deformation accumulation, and three typical deformation rate profiles of the representative observation points on the dam body. Finally, the power function model is used to predict the typical deformation observation points. The results of this paper indicated that: (1) the surface deformation of the tailings dam can be categorized into two directions: the upper portion of the dam moving away from the satellite along the Line of Sight (LOS) at a rate of −40 mm/yr, whereas the bottom portion approaching the satellite along the LOS at a rate of 8 mm/yr; (2) the deformation of the dam body is mainly affected by the inventory deposits and the construction materials of the dam body; (3) according to the current trend, deformation of two typical observation points in the LOS direction will reach the cumulative deformation of 80 mm and −360 mm respectively. The research results can provide data support for safety management of No.4 tailings dam in the Dexing Copper Mine, and provide a method reference for monitoring other similar tailings dams.

Urban land subsidence threatens the safety of urban buildings and people’s lives. The time series interferometric synthetic aperture radar (InSAR) technology can provide us with large-area, high-resolution, and high-precision ground deformation monitoring. In this study, the time series InSAR technology and the strategy with long- and short-time baseline networking are used to obtain the surface deformation along the line of sight of Nanchang City based on the six-year (from December 2015 to December 2021) Sentinel-1 data. Longer datasets and better baseline strategies allow us to obtain more stable deformation results of Nanchang City than other researchers. The results of surface deformation show that the overall surface of Nanchang City is stable, but there are several obvious subsidence funnels. We carried out a field survey on four areas with significant surface subsidence. We considered that these subsidence areas may be related to soil compaction, building construction, and groundwater extraction. Based on the surface deformation results around the subway line, we analyzed the impact of subway construction on the surface along the line and identified the sections that need to be focused on by the managers to prevent the deformation area from affecting the surrounding buildings and subway line operation safety.

In this article, we develop two target parameters to model the interaction between a target and a polarization wave. The two parameters are the target ellipticity angle (TEA) and the target phase angle (TPA). The concept of reflection symmetry or rotation symmetry is used to explain the robustness of the estimation method and to show problems associated with other algorithms. C-band Radarsat-2 and L band ALOS PALSAR multi-look full polarimetric images are used to substantiate the parameters, and validate the effectiveness of them. In addition, the TEA and TPA are compared with $\alpha - \beta $ model and Touzi TVSM model for single-look polarimetric SAR data. Experimental results show that the two target parameters are beneficial supplements for interpreting the target scattering processes and separating buildings from other targets.

The COVID-19 pandemic has been a great challenge to society, the economy, and population health. It has become a significant public health event and social problem. Exploring the impact of COVID-19 on the accessibility of outdoor sports venues is crucial for people’s health. Based on spatial theory, the quantitative and qualitative analyses of outdoor sports venues’ spatial distribution and accessibility were conducted, and the epidemic’s impact on them was analyzed. The results show that: (1) The existing outdoor sports venues in Nanchang show a distribution pattern of “sparse in the north and south, and strong aggregation in the middle”. (2) As a result of the epidemic, the center of the standard deviation ellipse in outdoor sports sites shifted to the southeast, while the number of open venues decreased by 68%. (3) Before COVID-19, the entire study area could achieve full coverage by driving for 17 min, riding for 70 min, or walking for 119 min. After COVID-19, the time increased to 29, 109, and 193 min, respectively. (4) Under the high-risk scenario of COVID-19, the average walking time for people to reach outdoor sports venues increased from 6.2 min to 14.0 min in the study area, with an increase of 126%. Finally, according to the findings of this study, recommendations were made on how government departments could build or re-open outdoor sports venues during and after this epidemic.

Ground subsidence is a representative geohazard in mining areas that threatens human safety and infrastructure. Interferometric synthetic aperture radar (InSAR) was used to measure ground subsidence related to mining activities. However, mining areas are often subjected to severe temporal and geometric decorrelation problems, resulting in sparse persistent scatterers (PSs) and lower measurement accuracy. To improve deformation measurements, a robust multitemporal InSAR (MT-InSAR) method that jointly detects PS and distributed scatterers (DSs) in a two-tier network was utilized here. To solve the mismatch in the traditional linear velocity model, a logistic model was introduced for MT-InSAR processing. Forty-four Sentinel-1A SAR images acquired between 1 January 2020 and 30 June 2021 were used to measure ground subsidence in Zhoutaizi Village, Chengde City, Hebei Province, China, which endured geohazards induced and exacerbated by mining activities. We observed that more measurement points were produced using the logistic model (11 607) compared with the constant velocity model (10 980) in the mining areas with an increase of 5.7%, while the mean value of the standard deviation of the estimated residuals reduced from 1.45 to 1.13 with a decrease of 22%. Results are beneficial for geohazard assessment and management in mining areas.

The helicity asymmetry parameter $\tau $ in the Cameron decomposition indicates the degree to wh ich a scatterer deviates from being an ideal symmetric scatterer. However, the solving procedure of $\tau $ can only be expressed in terms of single-look Sinclair scattering matrix. In this article, we extend the helicity $\tau $ to a generalized helicity parameter $\tau _{g} $ , which is appropriate for both the single- and multi-look polarimetric synthetic aperture radar (PolSAR) data. For single-look data, the generalized helicity $\tau _{g} $ is equivalent to the previous helicity $\tau $ . In addition, we investigate the relationships among the classical helix/helicity definitions, including the Cameron helicity, the Krogager helix component, and the Yamaguchi helix component. To achieve this, we represent the Cameron and Krogager decompositions in terms of the unified coherent polarimetric decompositions (CTD) model in the format of coherency matrix and revise the expression of Krogager decomposition contributions in function of Huynen parameters. Results show that essentially the Cameron helicity and Krogager helix are two kinds of representation of reflection asymmetry under the same decomposition model, and the Yamaguchi helix contribution is always larger than the Krogager helix contribution. Single-look PolSAR data from L-band ESAR are used for demonstration in this article. Several multi-look datasets are generated by $1\,\,\times \,\,3$ , $3\,\,\times \,\,3$ , $3\,\,\times \,\,5$ , $5\,\,\times \,\,5$ , $5\,\,\times \,\,7$ , $7\,\,\times \,\,7$ , $7\,\,\times \,\,9$ , and $9 \times 9$ boxcar average. Two techniques are taken to mitigate reflection symmetry assumption based on helix component and helicity angle, respectively. It will be shown that the technique with the generalized helicity $\tau _{g} $ performs best in terms of efficiency and stability.