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Objectives: The ground-based radar has features such as working all-time in all-weather, providing continuous observations with high spatiotemporal resolutions and can monitor landslides with high precision in near real-time. However, atmospheric effects represent one major limitation of ground-based radar, due to the spatiotemporal variations of the troposphere, especially in mountainous areas. Atmospheric variations are often treated as static signals and corrected by the range function model which can be unreliable, particularly when strong dynamic atmospheric turbulence occurs. Methods: Based on its successful experience in the generic atmospheric correction online service for interferometric synthetic aperture radar (InSAR), the ground based iterative tropospheric decomposition (GBITD) model is utilized to decompose the tropospheric delay into stratification and turbulence components, and perform atmospheric correction. The GBITD model doesn't require global navigation satellite system or any external meteorological observations, which makes it flexible for InSAR atmospheric correction. Results: The application of the GBITD model to the 2018 Baige landslide suggests that the root mean square of two interferograms with temporal baselines of 2 min and 10 min decreased from 1.43 mm and 1.69 mm to 0.21 mm and 0.24 mm, respectively. The maximum cumulative displacement derived from the 778 images acquired during the period from 4 to 10 December 2018 was 1.4 m with the maximum displacement rate of 0.23 m/d. Conclusions: The experimental results show that the GBITD method performes best compared against the homogeneous model and the stratified model in complex mountainous areas. Furthermore, Ground-based radar has obvious unique advantages in landslide monitoring, which can provide strong technical support for landslide emergency monitoring and risk assessment. [ABSTRACT FROM AUTHOR]

Objectives: Millimeter wave radar has been widely used in automotive industry and other fields, but its application is mainly limited to the environmental perception of obstacles or specific tasks. At present, there is little research on the application of millimeter wave radar in the field of navigation and positioning. Methods: This paper first studies the raw data processing principle of millimeter wave radar, and then designs an indoor ego localization method which only depends on a low‐cost millimeter wave radar. The process mainly includes extracting centroid feature points using density based spatial clustering of applications with noise (DBSCAN) algorithm, matching centroid feature point pairs through nearest neighbor criterion, constructing nonlinear optimization function and solving positioning results using levenberg marquardt method. Results and Conclusions: Experiments show that indoor navigation and positioning can be solved in real time by using a low‐cost millimeter wave radar. Under static conditions, the average horizontal positioning accuracy can reach sub centimeter level (mean value is 0.82 cm and standard deviation is 0.47 cm). Under dynamic conditions, the absolute trajectory error can reach 0.66 m and the average heading angle error can reach 4.58°, which shows the feasibility of ego‐localization of low‐cost millimeter wave radar. Finally, this paper discusses the problems and feasible research ideas of low cost millimeter wave radar in navigation and positioning. [ABSTRACT FROM AUTHOR]

Objectives: Two earthquakes with a distance less than 40 km occurred in Menyuan, Qinghai Province, China, including Mw 5.9 earthquake on 26th January 2016 and Mw 6.7 earthquake on 8th January 2022. Methods: The interferometric synthetic aperture radar (InSAR) technique was utilized to process Sentinel-1A radar images from both ascending and descending tracks to retrieve high resolution coseismic surface displacement maps for these two Menyuan earthquakes. The coseismic surface displacements were then inverted to determine the fault geometry parameters and the non-uniform fault slip distributions with a dislocation model in an elastic half- space. Results: The results show that the 2016 Menyuan earthquake was a reverse event on a buried fault with a maximum surface displacement of 6.7 cm and 7.0 cm on the ascending and descending tracks, respectively. The maximum slip on the fault plane reached 0.53 m and concentrated at depths of 4 − 12 km. The 2022 Menyuan earthquake ruptured along the NWW - SEE strike with a maximum surface displacement of 78 cm in the satellite radar line of sight and a maximum fault slip of 3.5 m occurred at a depth of approximately 4 km. Conclusions: Considering the tectonic settings around the Lenglongling fault zone, the 2022 Menyuan earthquake is likely to occure in the western segment of the left‐lateral Lenglongling fault, with its western end extending westward to the Tuolaishan fault. By calculating the coulomb failure stress changes (CFS), it is inferred that the 2016 Menyuan earthquake generated considerable positive CFS which might have triggered the 2022 Menyuan earthquake. [ABSTRACT FROM AUTHOR]

Objectives: The Sichuan-Tibet railway is not only a state key project in China, but also the most difficult super project in railway construction history due to the most complex terrain and the active geological structure. Interferometric synthetic aperture radar (InSAR) has proved to be a critical tool for detecting and monitoring geohazards because of its wide coverage, high precision, and high efficiency. However, due to its side-looking geometry, InSAR faces serious geometric distortions in mountainous areas, particularly in extremely steep high mountain and gorge areas along the Sichuan-Tibet railway. Methods: Utilizing the full open-access Sentinel⁃1 data, which has the wide coverage and a short revisiting time, we carry out satellite radar geometric distortion and feasibility analyses along the Sichuan-Tibet railway. Taking into account synthetic aperture radar(SAR) imaging geometry, the variations of the incidence angles across the whole SAR image, and the passive geometric distortions, we present an integrated approach to accurately determine the areas with SAR geometric distortions. Results: Our results for Sentinel-1 data show that the areas with geometric distortions for observations with a single-orbit (i.e. ascending or descending) reach 31%—35% along the Sichuan-Tibet railway, whilst the geometric distortion areas reduce to 1.5% for observations with both ascending and descending orbits; furthermore, about 35% of the whole area is suitable for joint analyses with both ascending and descending observations. Conclusions: The quantitative result also reveals the feasibility to use the Sentinel-1 data to detect and monitor geohazards along the Sichuan-Tibet railway from the perspective of geometric distortions. It can not only improve the overall understanding of the applicability of Sentinel-1 based InSAR and the InSAR results interpretation in this area, but also provide a guideline for efficiently selecting other satellite SAR datasets for detecting and monitoring geological disasters along the Sichuan-Tibet railway. [ABSTRACT FROM AUTHOR]

Objectives: Zhouqu County in Gansu Province is highly prone to landslides. On July 12, 2018, a landslide blocked the Bailong River near the county, posing a serious threat to the life and property of local residents and the safety of infrastructure. The early identification of potential landslides around this area is of great significance to protect the life and property of local residents and the security of its infrastructure. Methods: Firstly, small baseline subset interferometry technology (SBAS‑InSAR) was adopted to identify the potential active landslides in the surrounding area of Zhouqu County, with the Sentinel‑1A satellite ascending and descending images from October 2017 to December 2018. Then, a combination of optical remote sensing image interpretation and field investigation is used to determine and identify potential landslides. The visual interpretation method can be used to identify landslides that have occurred or are occurring on the optical images. The field investigation was used to verify the landslide results identified by In‑ SAR and optical imagery to increase the effectiveness and accuracy of landslide detection. Results: A total of 23 active landslides were detected in the study area, with 16 active landslides detected on the ascending images and 11 on the descending images, with 4 active landslides having valid deformation information detected on both the ascending and descending images. Combined with the visual interpretation of optical remote sensing images and field investigation, the deformation characteristics of 4 typical landslides, including Jiangdingya, Mentouping, Suoertou, and Xieliupo Landslides, were analyzed. It was found that the deformation rates of Jiangdingya, Mentouping, and Xieliupo Landslides were significantly higher during the rainy season than during the non ‑ rainy season, and the Suoertou Landslide did not show a significant increase in the deformation rate during the rainy season but showed fluctuations in the deformation rate during the rainy season. Conclusions: The use of single‑orbit radar satellite data for landslide detection can easily lead to the missed detection of landslide hazards, and the combined use of ascending and descending radar images can improve the accuracy of landslide detection in steep mountainous terrain. The deformation rates of active landslides in the study area have a good correlation with rainfall. The results can provide supports for the geohazard mitigation and prevention in Zhouqu County. The strategy which combines optical imagery, field investigation, and time‑series InSAR can efficiently and accurately detect and monitor landslides over a wide area. [ABSTRACT FROM AUTHOR]

Surface ruptures and deformation of large earthquakes are important for investigating earthquake mechanisms, fault activities and continental deformation. With the improvement of satellite techniques, op‐ tical and radar images have been widely used in earthquake studies since the 1992 Landers earthquake. However, due to a lack of pre ‐earthquake images, historical earthquakes prior to the 1990s are rarely studied. Recent declassification of American KeyHole (KH) satellite images opened up new possibilities of investi‐ gating old earthquakes back to the 1970s. Researchers have successfully applied KH ‐9 images to the 1978 Tabas‐e‐Golshan and 1979 Khuli‐Boniabad earthquakes in Iran, and gained some new insights into fault be‐ haviours. We first provided a review of the methodology and progresses of using KH ‐9 images to measure earthquake deformation, then investigated the 1976 Chaldiran, Turkey earthquake by matching the pre ‐ and post‐earthquake KH ‐9 images,and obtained an E ‐W displacement of about (3.1±0.7) m (i.e. strike‐slip), consistent with the measurements in the field. KH ‐9 imagery provides a new means of investigating histori‐ cal earthquakes in detail, but there are some limitations. These limitations are briefly discussed in the end. [ABSTRACT FROM AUTHOR]

Today, Sentinel ‐ 1A data with terrain observation with progressive scanning (TOPS) imaging mode is increasingly used in earth observation aiming at consistent monitoring of surface change and its deformation. However, due to the limited accuracy of coarse co ‐registration, spectral aliasing along the azimuth direction enables the presence of phase jumping in overlapping area of neighboring bursts. Although geometrical co‐registration in conjunction with enhanced spectral diversity (ESD) is proven to be a feasible strategy to correct such error and has been widely used in some open source softwares (e.g. DORIS (Delft object‐oriented radar interferometric software), SNAP (sentinel applications platform), ISCE (InSAR scientific computing environment)), the performance of ESD is still not satisfactory and relies strongly on spatiotemporal decorrelation. Given that decorrelation is generally quantized by interferometric coherence, this paper presents and assesses a new methodology to improve the accuracy of ESD by fully exploring the high coherent targets. Specifically, this method focuses on mitigating the spatiotemporal decorrelation in fine coregistration procedures by: (1) Selecting stable targets with moderate and high coherence using accurate coherence estimation. (2) Maximizing coherence magnitude by optimal interferometric subset chosen from Dijkstra algorithm. We compare and test this method against current favorites based on single master image and network‐based enhanced spectral diversity (NESD), and the experimental results demonstrate the value of our method. It can make up for the shortage of NESD method. [ABSTRACT FROM AUTHOR]

To solve the problem of high precision calibration of three‐dimensional baseline of space‐borne distributed interferometric synthetic aperture radar （InSAR） , a new method of baseline calibration is proposed. Firstly, this method combines the slave radar Doppler equation and the slave radar distance modification equation to form the baseline calibration model. Based on the ground control points, the least square iteration is used to solve the baseline three axial errors. Compared with the baseline calibration model based on the slave radar distance modification equation, the baseline calibration model optimizes the coefficient matrix condition number of the normal equation, reduces the morbidity of the matrix, and improves the calibration precision. Then, according to the baseline calibration, the baseline vector is actually used to intersect by the ground control points, and the intersection angle can be increased to improve the accuracy of the intersection. The control point layout strategy is given, that is, the control points are laid separately at the near and far ends of the radar footprint at ground. Compared with the way of laying control point uniformly, we can significantly improve the calibration precision and robustness. Finally, the spaceborne distributed InSAR simulation data was used to carry out the baseline calibration experiments based on different control points number, different control points precision, and different control points layout. The experiments show that the new method can achieve high ‐ precision result of three ‐ dimensional baseline calibration, namely, millimeter‐scale in cross‐track, along‐track and radial baseline direction respectively, which can provide a new way for the baseline calibration of spaceborne distributed InSAR . [ABSTRACT FROM AUTHOR]

Three-dimensional phase unwrapping is one of the key steps of time-series interferometric syn- thetic aperture radar (InSAR) technology. The unwrapping results directly affect the accuracy of time-series InSAR land subsidence monitoring. Aiming at the problem of the whole period unwrapping error caused by phase undersampling in areas with serious land subsidence and large change of terrain slope, a weighted least squares phase unwrapping algorithm based on frequency confidence is proposed, which replaces the weighted least squares phase unwrapping algorithm based on phase gradient in the time-dependent three-di- mensional phase. By improving the accuracy of phase slope change estimation, the accuracy and stability of spatio -temporal three-dimensional phase unwrapping can be improved. The land subsidence results of the typical area in Beijing are obtained by using the improved spatio-temporal three-dimensional phase unwrap- ping method. Compared with the classical spatio - temporal three - dimensional phase unwrapping method, the improved method can obtain higher accuracy of land subsidence monitoring results. Especially for the subsidence funnel region where the slope changes greatly and the decorrelation exists obviously, the subsid- ence monitoring accuracy has improved significantly. [ABSTRACT FROM AUTHOR]

Landslide is the second only to earthquake as one of the most serious geological hazards， which occur most frequently and cause the most serious losses. It poses a great threat to people9 s lives and property safety. In order to monitor dangerous landslides dynamically, GPRI-II groundbased radar system is used in this experiment to study the key technology of landslide deformation time series analysis, and the main process of ground-based radar data time series processing is formulated. It is applied to the stability monitoring of a road slope in Shaoxing，Zhejiang Province. The experimental results show that there is an obvious deformation area in the slope，which is located in the accumulation area of the construction site，and the maximum deformation is 3. 5 mm/d. At present，ground-based radar has the ability to monitor deformation with sub-millimeter accuracy when the observation conditions are satisfied. Ground-based radar has become one of the important means of disaster early warning and control. [ABSTRACT FROM AUTHOR]

In order to promote the wider use of ground-based synthetic aperture radar (GB-SAR) in the field of surface micro-deformation monitoring, this paper summarizes the main types of GB-SAR and introduces the working principles and important parameters of some representative systems. By taking the S-SAR (slope-synthetic aperture radar) ground-based radar independently developed by the China Academy of Safety and Production Science as an example，the key processing techniques utilized by the GB-SAR are introduced. Experiments verify the accuracy of GB-SAR. It also shows the application of GB-SAR in open pit mine slope monitoring，mine dumping site and landslide emergency rescue. Finally，the problems and suggestions of GB-SAR in monitoring are proposed. [ABSTRACT FROM AUTHOR]

As one important part of post-earthquake loss assessment, building damage detection has important significance for understanding the disaster in time, implementing the emergency response, and post-disaster reconstructing. In recent years the development of the multi-platform remote sensing and the high-resolution remote sensing technology have provided opportunities to building damage detection with high accuracy. In this paper， firstly，the basic building damage characteristics and the concrete classification criteria are introduced. Then，the common damage detection methods at home and abroad based on the remote sensing technology are concluded，including the single-temporal image detection of the post-earthquake, the change detection between the pre-earthquake and the post-earthquake images，and the damage detection based on the multi-sources data. Limitations and drawbacks of these methods are proposed. Finally, combining with some cutting-edge technologies in remote sensing domain，the latest research progress of building damage detection based on the high-resolution remote sensing technology，synthetic aperture radar technology，light detection and ranging technology 9 and oblique aerial photography technology are summarized in detail. [ABSTRACT FROM AUTHOR]

Satellite remote sensing has made great strides in the last few decades, which enables the long-term consistent observations of many variables of the terrestrial water cycle and thus advances the understanding of the terrestrial water cycle. This paper reviews the principles of remote sensing in retrieving key variables of the terrestrial water cycle, illustrates the progress of satellite remote sen-sing in hydrological applications, and discusses the future direction. Although most of hydrological states and fluxes variables are observable by remote sensing, closing terrestrial water budget with the remote sensing products is still an open question, suggesting more efforts are needed to improve the hydrological consistency of the remote sensing products. In the future, efforts should be made to develop new generation sensors and platforms for the consistent remote sensing products with finer spatiotemporal resolution. At the same time, efforts should be devoted to the evaluation of remote sen-sing products of the terrestrial water cycle through carrying out integrated field experiments. [ABSTRACT FROM AUTHOR]

Signal echoes from radar targets are usually buried in thermal noise and clutter, reflected back to the receiver by buildings, clouds, and the sea. The clutter-plus-noise power is not known at any given location, thus a fixed-threshold detection scheme cannot be applied if the false alarm rate is to be controlled. A class of schemes that can be used to overcome the problem of clutter; the constant false alarm rate (CFAR) processing schemes, set a threshold adaptively based on local information of total noise power. CFAR detection of radar targets can be implemented by a sliding-window detection approach or through the clutter map technique. The clutter map technique is often used for the radar target detection in a non-homogeneous background where the clutter power in spatial domain changes abruptly. However, the detection performance of the classic Nitzberg's clutter map on a non-Gaussian distributed background with a heavy long-tail greatly degrades. In our work, a new clutter map detection method based on non-coherent integration is presented. The analytic results show that its detection performance improves in a more spiky clutter environment, and it can be easily implemented. [ABSTRACT FROM AUTHOR]