最新刊期
卷 22 ， 期 S1 ， 2018
- 摘要：The ionosphere is an atmospheric region ionized by solar radiation, cosmic rays, and various particle radiations ranging from 60 km to 1000 km above the earth. Numerous free electrons and ions in the ionosphere can interfere with radio signals. Ionospheric parameters, especially F2 layer critical frequency (f0F2) and electron density peak height (hmF2), play an important role in the propagation of HF waves. Therefore, the study of f0F2 and hmF2, especially its global distribution, is important.The overall objective of this paper is to study the annual, diurnal, and seasonal variations of f0F2 and hmF2 in the world on the basis of GNSS occulation datasets and to compare the values f0F2 obtained by GNSS occultation and digisondes from all stations in Japan.COSMIC, GRACE, and CHAMP electron density profile datasets and digisonde datasets in Wakkanai, Kokubunji, Yamagawa, and Okinawa for 2002—2016 are selected as the data sources. The maximum electron density NmF2 and hmF2 is obtained by using the electron density profile. Compared with ionosonde f0F2 datasets, the latitude and longitude of the selected NmF2 are within 5 degrees of ionosondes, and the time of the selected NmF2 is within 15 minutes of ionosondes.Results show that the annual variation of f0F2 and hmF2 has a significant positive correlation with solar activity and geomagnetic activity and significant spatial distribution characteristics. The maximum value of f0F2 distribution on both sides of the magnetic equator is approximately 15 degrees, and the maximum value of hmF2 distribution in the equatorial region and the northern and southern hemisphere peak heights is not symmetrical. In addition, the peak value of f0F2 and hmF2 appears during LT 14:00—16:00, and hmF2 exhibits significant equatorial ionization anomaly recovery after sunset. The f0F2 has obvious seasonal characteristics; the peak value of f0F2 appears in spring and autumn at middle and low latitudes, and is evident in abnormal winter phenomenon. However, the seasonal distribution of hmF2 evidently change. The values f0F2, which were obtained by occultation and digisondes from all stations in Japan, were compared, and results indicate that the ionospheric parameters obtained by the two detection methods have acceptable correlation. The correlation in the Okinawa station is the best, with a correlation coefficient of 0.88. The correlation in the Wakkanai station is poor, with a correlation coefficient of 0.75. The correlation between Yamagawa and Kokubunji stations is close at 0.84 and 0.85, respectively.The preliminary study shows that the global f0F2 and hmF2 distribution is affected by many factors, including solar activity, geomagnetic activity, electric field, and wind and high-energy particle sedimentation.The values f0F2 obtained by occultation and digisondes from all stations in Japan were compared, and results show that the ionospheric parameters obtained by the two detection methods have acceptable correlation. However, some evident differences were observed; these differences may be due to the electron density gradient and satellite retrieval technology.关键词：annual variation of;f;0;F;2;and;h;m;2;diurnal variation of;2;seasonal variation of;2;digisondes;GNSS
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发布时间：2021-06-17 - 摘要：Devastating earthquakes are one of the most serious natural disasters that affect mankind. Although humans cannot predict or prevent earthquakes, we can change the way we respond to them. Earthquake-induced building damage is one of the main causes of casualties and property loss. Extracting the information of post-earthquake buildings quickly and accurately is crucial for identifying earthquake-induced building damage and initiating effective rescue of survivors. The geographical environment is complex in the seismic field, and remote sensing technology is a potential alternative to capturing post-event scene data. Numerous studies have focused on researching intact buildings. The identification of building seismic damage based on airborne Light Detection and Ranging (LiDAR) is studied only by using object-oriented analysis, and few papers use the characteristics of building points. This paper proposes a method that extracts building points in the earthquake zone from airborne LiDAR point cloud data.This paper treats the fast and reliable extraction of the information of a post-earthquake building as a challenging task in which many difficulties arise because of airborne LiDAR point cloud data, and pre-existing methods cannot easily achieve the desired effect. Therefore, this paper presents a method that combines aerial images and LiDAR data to extract post-event building points in the affected quake areas. The approach consists of several steps. We first extract terrain points from the LiDAR point cloud by using the cloth simulation filtering algorithm, and off-terrain points are removed. Then, we manually collect training samples of building and vegetation points and identify the red band as the best spectral characteristic information to maintain two isolated points. This procedure is based on the minimum probability of total error. Afterwards, we assign the gray value of the aerial image red band to the terrain points (which mainly include buildings, vegetation, pedestrians, and vehicle). The vegetation points are eliminated from off-terrain points by using gray-level histogram threshold segmentation. We used the density-based spatial clustering of applications with the noise (DBSCAN) algorithm to extract the final building points from the rest of the laser footprints, which contain discrete noise points.We can obtain intact and destructive building points from the LiDAR point cloud by using techniques such as point cloud filtering and threshold segmentation based on the gray intensity of the red band. However, some low-density noise points on the road, such as vehicles, pedestrians, and vegetation, can be obtained. The high-density building points remain nearly constant, and discrete low-density noise points are removed effectively by using the DBSCAN algorithm.The extracted point cloud of a building is compared with reference points to quantitatively verify the extraction accuracy. The false-dismissal probability and false-alarm probability are 15.61% and 7.52%, respectively. The two main causes of undetected error are as follows: (1) The damaged building points, which have a similar height as the ground points, are filtered when the point cloud filter is executed. (2) The building points in the shadow of tall buildings or trees are divided into vegetation points during threshold segmentation. False-alarm error is due to crowded vehicle points in local areas, and these points cannot be removed by using the DBSCAN clustering algorithm. The two errors are small, and the total extraction accuracy is as high as 84.39%, thereby indicating that the extraction of building points in quake-hit regions satisfies requirements in some bounds of precision with the application of the aforementioned method.Results show that the suggested method can effectively extract building points in the earthquake zone within a certain accuracy requirement and provide technical reference for the extraction of post-earthquake intact or destroyed buildings by using airborne LiDAR point cloud data. The proposed approach could establish the foundation for identifying seismic building disasters and completing post-earthquake building damage assessment.With the development of laser radar technology, an airborne LiDAR remote sensing system can receive dense point cloud data while acquiring multispectral or hyperspectral data. Hence, we will improve the ability of the proposed approach to distinguish between vegetation and buildings by using threshold segmentation based on normalized difference vegetation index or other band combinations to further improve the accuracy of building point extraction in the seismic field.关键词：airborne LiDAR;aerial imagery;the earthquake zone;building point cloud;DBSCAN (Density_Based Spatial Clustering of Applications with Noise) clustering algorithm
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发布时间：2021-06-17 - 摘要：Landslides are the most common geological disasters that result from large seismic activities and heavy rainfall in mountainous areas. They are destructive events that occur suddenly and have a wide distribution range. Landslide extraction is the primary factor in collecting destruction information and plays a key role in disaster prevention and emergency rescue. This paper presents a method that combines texture analysis and emissivity estimation to extract landslides from different backgrounds. Many researchers have focused on landslide extraction and recognition, and they proposed methods based on the ability of the Normalized Difference Vegetation Index (NDVI) to separate vegetation. However, although NDVI easily extracts landslides from high vegetation areas, it is affected by soil interference in sparse vegetation areas. Thus, extracting landslides is difficult. An NDVI-based method is proposed for landslide extraction in a complicated environment and to make NDVI effective in sparse vegetation zones.In accordance with the research area and remote sensing data, this method consists of four steps on the assumption that image preprocessing has been completed. First, the NDVI image is calculated by using near-infrared and red bands; this approach shows that some local regions have a sharp contrast, whereas others have a weak contrast. Second, texture analysis is conducted to divide the research area into several blocks according to this contrast distribution. NDVI mean and near-infrared Angular Second Moment (ASM) based on Gray-Level Co-occurrence Matrix (GLCM) could be selected as the texture feature to segment zones easily by providing simple thresholds. A continual large vegetation area is outstanding in the Mean feature, and a mountainous landslide area is rough in the ASM feature. The remaining area, except the first two, varies in the ASM feature related to soil components. Thus, the combination of Mean and ASM features facilitates texture analysis. Third, emissivity is estimated in different blocks based on the NDVI image. In this section, the NDVIs of pure soil and pure vegetation from statistics of the NDVI image in different blocks are critical parameters in calculating the Percentage of Vegetation (PV), thereby obtaining the emissivity. In a limited area, emissivity contrasts within different objects, especially for soil and vegetation, thereby making it more suitable than NDVI for landslide extraction. Finally, the landslides are extracted through emissivity threshold segmentation technology with an appropriate threshold manually.Landsat 5 TM and Terra ASTER data are tested by this method, and the result is favorable given that it is more consistent with that of artificial landslide extraction than that of the other methods, such as maximum likelihood supervised classification, neural net supervised classification, support vector machine-based supervised classification, and NDVI global threshold segmentation. For objective and quantitative evaluation, the result of artificial extraction is considered as the ground-truth data to calculate the confusion matrix of other results, with the Kappa coefficient being used to demonstrate the performance of each method. As a result, the method described in this article achieves a high Kappa coefficient, namely, 0.8531 (TM) and 0.9271 (ASTER). By contrast, maximum likelihood classification achieves 0.7634 (TM), neural net classification achieves 0.66 (TM), SVM-based classification achieves 0.6896 (TM), NDVI global threshold (0.3) segmentation achieves 0.622 (TM), and NDVI global threshold (0.5) segmentation achieves 0.7487% (TM). Evidently, this method can effectively eliminate omission and misclassification. With the increase in the resolution of remote sensing data, ASTER (15 m) provides a better result compared with TM (30 m), thereby showing that this method does not rely on data sources, and a high resolution contributes to a good result.Comparative analysis between different methods and data sources indicates the following results: The NDVI mean and near-infrared ASM are good texture features for separating different background environment blocks, especially with soil as the leading factor. Emissivity reflects the spatial difference in objects, although it is estimated by NDVI. The estimated emissivity not only separates vegetation from NDVI but also increases the difference between soils, thereby resulting in good landslide extraction. The advantages of texture analysis and emissivity estimation enhance landslide extraction in complicated research areas. Finally, the threshold selection problem in NDVI global threshold segmentation method is solved, and the sample selection and learning process in supervised classification are avoided. This method is designed for a medium resolution that ranges between 10 m to 50 m; thus, this method can be used with other data sources with a similar resolution, such as Landsat 5 TM and Terra ASTER. We proposed an effective method for landslide extraction for medium resolution. To handle high-resolution remote sensing data, this method will be combined with object-oriented methods in follow-up studies for accurate landslide extraction. The proposed method has a strong dependency on manual threshold selection; this dependency is inconvenient in the auto-extraction process. Therefore, self-adaptive threshold extraction is another challenge in future work.关键词：landslide extraction;Emissivity;Texture analysis;disaster remote sensing;diverse background;threshold segmentation
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发布时间：2021-06-17 - 摘要：Seismic ionospheric disturbance research shows that ionospheric change caused by seismic activity exists in seismic ionospheric precursory phenomena of space plasma change before an earthquake. For example, the electronic total content (TEC), electron density (Ne), ion density (Ni), electron temperature (Te), and ion temperature (Ti) are abnormal. Therefore, monitoring earthquakes and providing an early warning is feasible by measuring pre-earthquake plasma changes. The Langmuir probe effectively detects space plasma and can be used to measure parameters such as electron density and electron temperature. The feasibility of the Langmuir probe in seismic remote sensing observation is studied based on the mission of the China seismo-electromagnetic satellite.The Langmuir probe payload consists of three parts: a sensor, an extension rod, and an electronics box. The sensor has a spherical configuration; its upper hemisphere is a collecting electrode, and its lower hemisphere is a protective electrode. The same sweep voltage is applied to the upper and lower hemispheres to eliminate the terminal effect of the connecting point between the traditional spherical structure and the boom. The sensor surface is coated with TiN material to ensure uniform surface work function and to prevent space atomic oxygen erosion. The Langmuir probe is designed with two sensors, each of which is redundant.The plasma environment calibration test of the Langmuir probe flight model was conducted in INAF-IAPS. The test method measures the electron density and temperature at six different distances from the plasma source and compares the results with the measured results of the INAF-IAPS reference Langmuir probe. The calibration test result shows that the Langmuir probe test data are consistent with the test data of the INAF-IAPS reference Langmuir probe. Thus, the design of the Langmuir probe can achieve the missions of the satellite.The scientific data of the Langmuir probe include level 0, level 1, and level 2 data. The interference is removed from the raw data, the error is corrected, and repetition is eliminated to generate level 0 data. The level 0 data are revised by calibration parameters to produce level 1 data, which are preliminary physical data. The level 2 data are the final physical data, which contain geographic and geomagnetic coordinates, satellite time, space position, and satellite attitude information.With the launch of the China seismo-electromagnetic satellite, the Langmuir probe is applied for the first time in the field of earthquake remote sensing observation in China. The electron density and temperature are obtained by the Langmuir probe, and the ion density and temperature are obtained by a plasma analyzer. Other space electromagnetic information is obtained by an electric field instrument and a magnetometer. These data are studied synthetically to provide a new method for seismic stereoscopic observation and exploration for early earthquake prediction.关键词：Langmuir probe;seismic remote sensing observation;electromagnetic monitoring test satellite;ionosphere plasma;electron density;electron temperature
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发布时间：2021-06-17 - 摘要：Seismic hazard is closely related to Holocene active tectonics. A quantitative study of parameters, such as seismic slips, slip rate, and recurrence intervals of the active fault, is significant for scientific earthquake research. High-resolution Remote Sensing (RS) is effective for a large-scale quantitative study of active tectonics. However, many differences exist between active tectonics study and traditional geologic study with the use of RS. We should first establish a series of geomorphic markers to interpret many different active tectonics, which still lack effective guidance and a systematic conclusion.To direct the effective application of RS in quantitative research of active faults, we conducted several investigations based on RS images. First, the differences and correlations between active tectonic survey and traditional geologic survey, which mostly relies on the interpretation of macrogeomorphology or linear structural features, are discussed based on research developments through high-resolution RS. Second, the mechanisms of different fault models, including strike-slip, normal, and thrust faults, are introduced according to their stress-strain relations among maximum principal stress (Δσxx), intermediate principal stress (Δσyy), and minimum principal stress (Δσzz). The different relationships among the three vectors generate different structural environments and mechanical behavior. Three tectonic geomorphologic models are illustrated and delineated in the paper according to dynamic mechanics with field phenomena. A series of micro-tectonic geomorphogical features is generated by the three fault models.A series of interpretive markers of different tectonic geomorphologic indices related to the active tectonics is presented based on RS images. We divide the interpretive markers into three groups, namely, geomorphologic markers directly offset by a fault, tectonic geomorphologic markers derived from a fault, and indirect interpretive markers from an image. The first group can be identified directly from offset evidence conserved on the earth surface; it can also be used to determine the fault type and evaluate the offset amount of the fault. The second group can be used to determine the geometrical and kinetic features of the active fault, such as the pressure ridge, seismic bumps, pull-apart basin, and Redel ruptures. The third group is an indirect interpretive marker for the active fault. However, not all phenomena similar to the third group are related to the active fault. Image features of a non-active fault that may be related to human activity, natural erosion, or previous geological evolution are also analyzed in this study. These features may lead to the misinterpretation of active tectonics. Numerous examples of different markers, which are interpreted from important active faults of China, are presented in this study to guide the investigation of active faults. Different correlations among active faults, tectonic micro-geomorphology, interpretive markers, and image features are analyzed according to different cases.Each of the three fault models can generate many different interpretive markers. However, the three-fault model could also generate similar interpretive markers. In practice, no fault with one pure fault model exists in the field, and the fault usually behaves in superimposed mechanical mechanisms. In addition, the fault may also behave in different fault models in different segments along the fault zone. Therefore, studying an active fault by using interpretive markers is complicated. Field identification of active faults by verifying interpretive markers is necessary to supplement the evidence.The interpretive markers of different active faults are summarized by high-resolution RS images in this paper. The relational schemas supplied among different active faults, tectonic micro-geomorphology, interpretive markers, and image features are important for a qualitative and quantitative study of active faults. Our study provides beneficial guidelines for research of active faults on the basis of high-resolution RS images.关键词：remote sensing image;active fault;tectonic micro-geomorphology;interpretive marker;quantitative research
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发布时间：2021-06-17 - 摘要：An earthquake is a sudden natural disaster that results in the great loss of human lives and the compromised safety of properties. Rapid assessment of building damage after an earthquake is crucial for earthquake emergency rescue and damage assessment. Synthetic Aperture Radar (SAR) is an effective earthquake disaster analysis and evaluation method with a unique ability to overcome the impact of bad weather after an earthquake. Change detection based on SAR images is one of the important methods for remote sensing seismic information recognition.The conventional SAR image change detection method is mainly based on intensity images. Damaged buildings after an earthquake have complex and diverse forms, and no regularity exists in the intensity image. Therefore, capturing all the change information in the image under the set standard is difficult. However, the change in texture features is stable and cannot be affected easily by a change in ground features. Therefore, the inclusion of texture features in the calculation can completely obtain the change information of the image. Many parameters can describe texture features. If all the features are used, then the complexity of the algorithm is increased, and the feature information becomes redundant, thus reducing the accuracy of information recognition.To address irregular changes in intensity images after an earthquake and the numerous and difficult-to-optimize texture feature parameters, we propose a correlation change detection method based on principal component analysis of texture features. Principal component analysis is used to fuse multi-texture information based on the analysis of image texture features to avoid redundancy of features. Then, the window size is set to calculate the correlation between the extracted principal component components, and the correlation classification threshold is set for the detection of seismic building information. The process is mainly divided into four steps: (1) texture feature analysis; (2) principal component analysis; (3) correlation analysis; and (4) threshold setting and classification.The study considers Mashiki, which is the area that was most seriously damaged by the Kumamoto earthquake, as the study area. ALOS-2 SAR image data are used to verify the effectiveness of the proposed method, and the results are compared with those of the correlation change detection method on the basis of intensity image and with those of the difference change detection method on the basis of intensity image. Results show that the proposed method can efficiently extract buildings with different damage levels with an overall extraction accuracy that reaches 87.2%. The overall extraction accuracy is higher than that of the two change detection methods based on intensity images. The method not only obtains high extraction precision but also reduces misclassification probability.Principal component analysis can cover the useful information in the features and avoid the redundancy of features effectively. The change detection method based on SAR image texture feature can distinguish the intact and the destroyed buildings effectively. The proposed method can be used for allocating earthquake emergency rescue forces, damage assessment, and reconstruction.关键词：change detection;SAR;texture feature;correlation;Earthquake;building
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发布时间：2021-06-17 - 摘要：The internal structure of the Earth and its geomagnetic distribution and spatial environment can be studied by exploring the near-Earth magnetic field. The China Seismo-Electromagnetic Satellite (CSES) is the first satellite of this kind in a near-Earth orbit. Its scientific goals include the real-time monitoring of electromagnetic changes by studying the Earth system, especially the ionosphere and the mutual actions of other spheres. Obtaining information on ionospheric response before and after an earthquake is the main goal. The magnetic field is one of the most important physical parameters for monitoring the ionosphere. A High-Precision Magnetometer (HPM) is responsible for the accurate measurement of magnetic field vector components from DC to 15 Hz.The magnetic environment of the spacecraft and the vector value accuracy requirement for magnetic field detection are considered. The HPM consists of two fluxgate sensors and a CDSM scalar sensor. The fluxgate sensors provide the vector components of the magnetic field but with limited accuracy and long-term stability. The CDSM sensor measures the scalar of the magnetic field with high accuracy and stability and is therefore used to calibrate the vector data. Satellite remanence magnetic interferences can be reduced with the help of two fluxgate sensors.Several ground data processing methods used to obtain the actual accuracy vector magnetic field data were considered, including the physical calibration of the single sensor, the absolute vector correction algorithm, the remanence magnetic interference elimination, and the coordination conversion method. Several ground calibration tests were conducted to obtain the actual performances.This article also introduces the development of sensors and electronics, as well as provides the data processing procedure and method, and the calibration results.Several algorithms were developed and presented in this article according to the requirement of the ground data processing method. Several key calibration tests were conducted to obtain the linearity, the thermal drift results, the coordination relations between the FGM magnetic axis and the sensor structure, the disturbances of sensors, and the heading error of the CDSM sensor. The results are shown in the table below. Calibration results show that the performances of the HPM satisfy the specifications.HPM development provides a magnetic field exploration method for a near-earth orbit satellite. The schedule indicates that HPM has completed all development and calibration works before the satellite launch. All the performances and data processing procedures satisfy the requirements defined for the CSES mission.关键词：CSES;HPM;fluxgate magnetometer;CPT magnetometer;magnetometer calibration
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发布时间：2021-06-17 -
Temporal and spatial characteristics of the 2008 Wuqia, Xinjiang M6.7 earthquake multiple parameters
摘要：Seismic thermal anomalies have attracted increasing attention from the scientific community since they were proposed in the mid-1980s. A long-term Outgoing Longwave Radiation (OLR) data set from 2007 to 2016 was used to analyze thermal anomalies in the magnitude 6.7 earthquake that hit Wuqia, China, on October 5, 2008. To identify the earth-atmosphere system’s multiple parameter variations related to earthquakes, other surface and atmospheric multi-parameter data were processed over the critical region of Thermal Infrared Radiation (TIR) anomalies.Nighttime NOAA OLR data were selected because capturing seismic anomalies at night is easier than in the daytime considering the effect of artificial anomalies and solar radiation. The vorticity method was used in this study. To reliably detect seismic precursory information, 2009—2011 data on the absence of significant seismic activity in the Xinjiang region were calculated as background field. Apart from vorticity spatial analysis, time series analysis was utilized in this study. Then, the coupling variation of multi-parameter data was analyzed according to the Deviation-Time-Space (DTS) method.The 10-day average OLR vorticity analysis shows a sudden increase of OLR in mid-September 2008. Moreover, a long-term OLR data analysis showed that the anomalies existed prior to the seismic case only, which can be considered a unique variation. The OLR anomalies were not observed in aseismic years, thereby showing that OLR anomalies were related to the Wuqia earthquake. The OLR anomaly is located on the boundary of the Tarim active block. Therefore, distinguishing the seismic precursor is important. The strong-body earthquake-generating model indicates that the irregular boundary of a solid block is likely to accumulate stress. The Tarim tectonic block has been stable since the Cenozoic era and can be classified as a solid body. Previous studies have shown a strong correlation between stress changes and TIR. The enhanced TIR between the active blocks was due to non-continuous stresses and high energy accumulation induced by the interaction of the active blocks and the strong differential movement between them.The increasing TIR anomalies prior to the earthquake led to heat accumulation on the near-surface and the near-ground air, resulting in the variation of skin temperature, air temperature at the lower height pressure levels, and relative humidity of air. The behavior indicates the coupling relationship between the lithosphere and the atmosphere in the seismogenic region.We deduce that air pressure is one of the external trigger factors of earthquakes. The dramatic variation of air pressure during the seismogenic process might affect the critical state. As soon as all internal conditions (the active seismic structure, the nature of the seismogenic zone, the crustal stress environment, and the focal mechanism) exist, some external conditions may trigger an earthquake.The increase in CO degasing in this case is only at the 800 hPa pressure level, thereby indicating that the source of CO variation is mainly the near-ground surface over the seismogenic zone and appears four days after the shock. The post-seismic variation might be related to the nature of seismogenic structure (locked and extrusion pressure-controlled) and the aftershocks.The surface and atmosphere multi-parameter variations associated with the 2008 M6.7 Wuqia earthquake were analyzed to detect precursor information related to the earth-atmosphere system. OLR anomalies were detected on the boundary of the Tarim active block because stress easily accumulated along a solid block boundary. The enhanced TIR emissions are reflected in anomalous OLR data. Results showed that the spatial location of OLR anomalies could reflect the crustal stress accumulation. Furthermore, OLR, skin temperature, air temperature, and relative humidity showed quasi-synchronous variations before this case. Results supported the seismic multi-sphere coupling model. The multi-parameter coupling between the surface and the atmosphere is an important precursor indicator in the short-term and immediate periods, and should be considered in future seismic infrared monitoring.关键词：outgoing longwave radiation;lithosphere-atmosphere coupling;multiple parameters;earthquake monitoring;satellite observation- 1142
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发布时间：2021-06-17 - 摘要：A coseismic displacement field is particularly important for earthquake studies. Since their launch in 2014 and 2016, ESA's Sentinel-1A/Sentinel-1B satellites have been acquiring large amounts of SAR images from all major plate boundary regions. Thus, these satellites are well suited for this task. We review the principle of Sentinel-1 imaging modes and the latest data process techniques through case studies of the 2014 Napa Valley, 2015 Nepal, 2016 Kumamoto, and 2016 New Zealand earthquakes. We introduce how to utilize the coherent and incoherent information of Sentinel-1 data fully to map coseismic displacements in near and far fields, along the line of sight and in along-track directions. The latest technical development and case studies show that we can derive not only a smooth coseismic displacement from the far field but also a displacement close to the rupture trace, demonstrating that the Sentinel-1 system plays an increasingly important role in earthquake studies.关键词：SAR, InSAR;Sentinel-1;coseismic deformation;radar remote sensing
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发布时间：2021-06-17 - 摘要：Multi-geophysical field observation is the main academic domain in research on earthquake preparation mechanisms, and satellite-based remote sensing technologies provide strong support for this study. To obtain a comprehensive understanding of the 2010 Yushu earthquake, the earthquake preparation process was studied based on multi-geophysical field observations.The regional strain field was inversed from GPS data, and co- and post-stress effects were discussed by applying the focal mechanism model from the Wenchuan earthquake to the Yushu earthquake to distinguish their relationship. Then, all the precursors to the Yushu earthquake were collected and classified by their occurrence time and the parameters of GPS strain, gravity, electromagnetic fields, and infrared.The independence of the Yushu earthquake in terms of its preparation process and occurrence was verified by using regional GPS stress and strain field results and with the stress-triggering effects of the Wenchuan earthquake used as basis. The developing time chart of various anomalous information of the Yushu earthquake, which occurred on April 14, 2010, was drawn by integrating multi-geophysical parameters and combining the related results of seismology, gravity field, geochemical, infrared, and ionospheric monitoring studies. The remote sensing technologies present special monitoring advantages in the region with sparse station distribution.The three typical preparation processes of the Yushu earthquake can be divided based on the corresponding response of multi-geophysical parameters, and the underground rock in different stress states can excite anomalies in different geophysical fields. GPS stress and strain fields are the main parameter in long-term earthquake monitoring, and the space electromagnetic field presents evident perturbations in the impending time period. The coupling process and connections among multi-geophysical fields require further investigation. Satellite-based remote sensing technologies play important roles in this earthquake analysis and show significant advantages in regions with few seismic stations.关键词：Yushu Earthquake;GPS strain field;multi-geophysical fields;preparation process
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发布时间：2021-06-17 - 摘要：The paper analyzed the relationship between an earthquake and a celestial tide-generating force. We selected the background that indicates the time for the research of the abnormal enhancement in identifying the atmospheric temperature rise caused by an earthquake based on the phase change cycle of tidal force. Then, with the use of atmospheric stratification, which is integrated with atmospheric temperature data from the National Center for Environmental Prediction, the air temperature evolution of several different levels in the vertical direction before and after the MS8.1 Kunlun Mountains earthquake was analyzed. Results show that the earthquake occurred when the tidal force value was near the maximum amplitude phase. Thus, the tidal force could trigger an earthquake near land surfaces and upper multi-layers. The warming areas are mainly concentrated near active faults, thereby exhibiting non-uniform heating procession. The temperature increased to a continuous evolution procession of warming before the earthquake and recession after the earthquake. It obeyed the rule of thermal rise procession of rock broken under stress loading. Thus, the increase in temperature was related to the activities of the regional fault. Meantime, the air temperature performed a warm procession, that is, the surface air is warmed by land, uplifted by heat flux, and cooled and dissipated in the sky. It is consistent with the dynamic diffusion principle of atmospheric air thermal warming by land in the vertical direction. The tectonic activity is the main cause of the abnormal change in temperature. Finally, the atmospheric warming process stepped with the tidal force (from low phase to high phase) change process. Therefore, the tide force not only delivered a mechanical basis and calculated the time to select the background in advance in research on air temperature warming during an earthquake but also showed that the atmosphere temperature change, according to the tidal force change cycle, could reflect the change in tectonic stress prior to an impending earthquake. Combining the analysis of the tidal force change and the analysis of atmospheric vertical temperature stratification distinguishes the increase in air temperature anomalies caused by the earthquake from that which is not caused by an earthquake.关键词：earthquake remote sensing;temperature anomaly;vertical distribution;celestial tide-generating stress;tectonic fault
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发布时间：2021-06-17 - 摘要：Strong surface or subsurface vibrations (e.g., aftershocks and blasting) may affect the stability of open-pit mining slopes. Slope stability evaluation is one of the important research topics in open-pit mining safety production. Ground-based InSAR has become a conventional method for monitoring micro-deformation. Similar to spaceborne InSAR, GB-InSAR calculates phase change along the line of sight (LOS) to inverse the deformation of an observation object and then transforms into deformation in a specific direction according to the projection between the LOS and the observation direction. The GB-InSAR system can be used to monitor the activity characteristics of an open-pit slope in near real-time and provide reliable data for safety production.We use a continuous observation mode and apply direct integration method to integrate the 25 interferograms formed by processing each SLC image with the subsequent one. The uniform atmospheric time-series correction factor is estimated based on the displacement variations over time for 12 ground control points selected on stable iron ores located away from the blasting areas.Results show that the observation accuracy is within -0.3 mm to 0.3 mm. Only one remarkable displacement sector is located in the lower part of the quarry rock face with a maximum cumulated displacement of ~4 mm. Time-series displacement analysis of pixels shows a slight sliding of not more than 0.3 mm in LOS after blasting and gradually becomes stable over time.The ground-based InSAR system has high observation stability. The blasting operation has no significant destructive effect on the entire mining face except for a slight decrease in the ore accumulation layer. The GB-SAR system can observe and recognize the deformation zone in a short time and plays an important role in investigating and evaluating slope stability and artificial landslide. The combined application of spaceborne and ground-based InSAR technologies will be further developed to realize the complementary advantages of both observation types based on the current research. At the same time, we will further develop the multi-baseline InSAR technique under repeated observations and introduce mature spaceborne InSAR processing methods to ground-based InSAR to expand its scope of application and enhance the stability of information extraction.关键词：ground-based InSAR;slope stability;ground-based InSAR time-series analysis;combined spaceborne and ground-based measurements
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发布时间：2021-06-17 - 摘要：Many electromagnetic emissions related to earthquakes have been observed by using space-based monitoring systems in the past decades. Such systems can operate together with ground-based monitoring networks to improve the capability to detect abnormal information related to earthquakes. The first French-developed satellite, known as Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions (DEMETER), is used for detecting ionospheric perturbations associated with earthquakes and volcanic eruptions. DEMETER has produced significant results, but the mission ended in 2010. However, the China Seismo-Electromagnetic Satellite (CSES) project began in 2013, and CSES will be launched in early 2018. CSES is proposed to be the first experimental satellite for earthquake-related electromagnetic emission monitoring from the ionosphere. This satellite is the first space observation platform within the 3D earthquake observation system in China. The objectives of CSES are as follows: (1) obtain worldwide data on space environment of the electromagnetic field, ionospheric plasma, and energetic particles; (2) monitor ionospheric perturbations in real-time when the satellite passes over Chinese territories and their adjacent area; and (3) investigate ionospheric perturbations that may be associated with earthquake activity, especially destructive phenomena. Eight scientific payloads, including search coil magnetometer, high precision magnetometer, electric field detector, GNSS occultation receiver, plasma analyzer package, Langmuir probe, high energy particle analyzer, and tri-band beacon, will be on board CSES to address the aforementioned objectives. All the payloads are used for monitoring the electromagnetic field, its disturbances, and the ionosphere environment. The payloads are also used to obtain the changing information of ionospheric structure below the satellite altitude. The detecting elements include electromagnetic field, plasma wave, electron density, electron temperature, ion temperature, ion composition, ion velocity distribution, and ion drift velocity. The CSES will provide an approach to studying the electromagnetic disturbances related to earthquakes, recognizing the regularity and mechanism of ionospheric disturbance, and studying atmosphere-ionosphere-lithosphere interactions. The data process method of CSES is a completely new research field for Chinese researchers, and the method has been developed in recent years. In this paper, we introduced the data catalog, data processing level, and the definitions thereof. The CSES data are divided into five levels (0—4). The general data processing procedure and the associated products were introduced. The data processing procedures of Levels 1 and 2 and the key algorithms of each scientific payload were described in detail.关键词：CSES satellite;data level;data process method and procedure;data product
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发布时间：2021-06-17 - 摘要：At 3:42 on July 28, 1976, a strong earthquake of magnitude Ms7.8 with a focal depth of 12 km and an epicentral intensity of XI degrees occurred in the Tangshan area of Hebei Province. The earthquake caused severe casualties and property losses and the most serious damage in Tangshan, but it also spread to Beijing and Tianjin. Equal intensity maps of the Tangshan earthquake were studied in detail by using relevant preserved data. After the Tangshan earthquake, significant departments conducted aerial photography for the first time and gathered the most valuable information for the earthquake damage distribution.Seismic damage information and sand-water blasting are interpreted and extracted by comparing KH satellite and aerial images before and after the earthquake, respectively. The image features for earthquake damage interpretation are summarized, and the meizoseismal area and damage zone are determined. Change detection in major counties is processed using aerial, KH, and Landsat MSS images before and after the earthquake. A total of 2495 building samples are selected, and the change detection of key villages and town targets is performed through correlation analysis. The damage degree and its trend are studied on the basis of change detection. The earthquake fault is analyzed using aerial images, aftershock distribution, and aeromagnetic images. Then, the intensity zone is determined by interpolating sample points through the method of inverse distance weighted interpolation. The seismic intensity zone of the Tangshan earthquake has been interpreted by combining multi-source remote sensing data. This map has finer details than previous results but with high similarity.This paper comprehensively used multi-source remote sensing data to realize the determination of seismic intensity zones. The results obtained are as follows： (1) The aerial images after the Tangshan earthquake were mosaicked, the characteristics of the earthquake damage in Tangshan were analyzed, and interpretation marks of the aerial images were established. (2) US KH satellite and aerial images before and after the earthquake, respectively, were analyzed comparatively. The damage to buildings in Tangshan City and its surrounding towns and the collapse rate information were extracted by using the change detection method based on object-oriented image processing. The 90.9% collapse rate of Tangshan City and its surrounding towns was calculated through a comprehensive analysis. (3) Landsat, aerial, and KH images of cities and towns before and after the earthquake were obtained, and 2495 building zone samples were clipped from images. Correlation coefficients were determined from pre- and post-earthquake images. The correlation analysis shows that the correlation coefficient is low from towns near the epicenter and high from towns far from the epicenter. This result is consistent with the actual situation. (4) On the basis of typical tectonic interpretation marks in aerial films, the active tectonic map of the Tangshan area was obtained using KH, aerial, and ETM images, which provide the information basis for the direction of intensity distribution. (5) On the basis of these results, with reference to the previous research intensity map, the threshold of correlation points was determined through statistical analysis. The intensity distribution area was identified by interpolating the sample data on the basis of the IDW interpolation method. The trend of intensity maps was simplified using seismogenic faults, historical earthquakes, and other tectonic data. The generated earthquake intensity has changed in detail, but it is similar to the field survey results.Rapid mapping of intensity maps after earthquakes is significant in deploying rescue work and reducing casualties and property losses caused by earthquakes. On the basis of remote sensing data, the intensity map was formulated, and it was revised using numerous methods for further precision and accuracy. With a variety of sensors and the launch of UAV photogrammetry and remote sensing, remote sensing technology will play an increasingly important role in drawing and revising seismic intensity maps. The seismic intensity assessment in this study requires a high level of sample data and a uniform distribution. In the future, additional samples should be selected to improve the accuracy of seismic intensity estimation.关键词：Tangshan earthquake;aerial photograph;KH images;seismic intensity zone;correlation analysis
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发布时间：2021-06-17 - 摘要：Satellite gravimetry is a technique of surveying the earth’s gravity and geoid and their changing signal. The data are used in geodesy science, environment monitoring, seismic, hydrology, and ocean science.An accelerometer is a core payload in the satellite-to-satellite tracking model or satellite gravity gradiometry and is used to sense non-gravity forces. An accelerometer cannot survey a non-conservative force absolutely for its bias, drift, scale, and second-order terms. Parameters change with the environment, status, and time. Thus, the accelerometer should be calibrated and validated.The accelerometer STAR is loaded on the Challenging Mini-Satellite Payload for Geophysical Research and Application (CHAMP) satellite and has an accuracy of 10-8—10-9 m/s2. The SuperStar accelerometer is loaded on the Gravity Recovery And Climate Experiment (GRACE) satellite, and its accuracy is improved to 10-9—10-10 m/s2. The GRADIO accelerometer is loaded on the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite, and its accuracy is 10-11—10-12 m/s2. With the improving accuracy, additional requirements are needed to calibrate the accelerometer.In terms of data type, the three calibration methods are as follows: The first method is direct calibration, where non-gravity force model data are used to compare the output of the accelerometer. The second is the dynamic method, where GNSS data are used to determine the satellite orbit and the accelerometer bias parameters together. The third is the integrated method, where all data are used to determine the total coefficients of the gravity model and the bias of the accelerometer. In addition, the energy domain, the cross point, and the gravity up-continue methods are used to calibrate the accelerometer. The energy domain method is based on persistence energy. The dissipative energy is deduced by the satellite position and velocity. Then, the parameters of the accelerometer are evaluated from the dissipative energy. Its accuracy is not better because the dissipative energy cannot be calculated precisely given the error of the satellite position and velocity. The cross point method is based on the hypothesis that the force of satellite, which crosses a point twice, is equivalent. Evidently, it is an inaccurate method. The gravity up-continue method is used to calibrate the gravity gradiometer. All these methods have been used to calibrate the accelerometer on CHAMP and GRACE. Results indicate that the dynamic and integrated methods are appropriate for external calibration. A new calibration method called the acceleration domain method is proposed. The calibration method is discussed, and the mathematic model is deduced.The acceleration domain method is used to calibrate the GRACE accelerometer. Results indicate that the total calibration accuracy is 10-8—10-9 m/s2. The best calibration is that of the X-axis parameters, followed by the Z-axis parameters, and then the Y-axis.The acceleration domain method effectively determines the accelerometer parameters. The calibration method is affected by the prior earth gravity model. Thus, iterative procedures should be applied. The accuracy of total acceleration, which is calculated from GNSS data, is related to the position sample rate. Thus, if the GNSS data rate is increased, then the calibration accuracy is improved. If the GNSS data rate is 1 s, and the calibration accuracy is 10-9—10-10 m/s2, then the accuracy is improved 8-10 times.关键词：satellite gravimetry mission;accelerometer;calibration;acceleration calibration method
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发布时间：2021-06-17 - 摘要：Low-low tracking gravimetric satellite Gravity Recovery and Climate Experiment (GRACE) with a spatial resolution of 330 km can detect gravity field change due to mass migration of the Earth. Numerous studies show that coseismic and postseismic gravity changes caused by several megathrust earthquakes (>Mw 8.8) in the ocean can be detected by GRACE. The gravity gradient satellite Gravity field and steady-state Ocean Circulation Explorer (GOCE) can provide a global gravity and geoid model with high accuracy and a high spatial resolution of 80 km. However, GOCE measurements cannot be used to detect gravity signals induced by any earthquake because of high-frequency noise. Previous studies focused only on the oceanic earthquake and gravity change but not fault creep during the interseismic period. In this paper, we simulate the gravity and gravity gradient changes caused by interseismic coupling of the Main Himalaya Thrust, as well as the coseismic rupture of the 2015 Nepal Mw 7.8 event.The MHT, where most crustal deformation occurs, absorbs half of the total India-Eurasia convergence rate (~20 mm/yr). Large earthquakes that recur along the Himalaya front must be related to the MHT rupture, for example, the 2015 Nepal earthquake. We first jointly invert the coseismic slip distribution of the 2015 Nepal event, which occurred at the seismic gap between the 1505 M 8.5 and 1934 M 8.2 events, using Markov chain Monte Carlo approach from GPS and InSAR observations. The InSAR data from ALOS-2 are resampled by using the quadtree technique. Green’s function is computed by using a spherically layered dislocation theory. The inverted average slip model shows that the maximum slip is approximately 6±0.7 m, and the seismic moment is approximately 1.02×1021 Nm, which is equivalent to Mw 7.9. The result is similar to that of other studies.Then, we invert the interseismic slip deficit of the MHT from GPS data that are post-processed by removing the block rotation effect based on the backslip model. The interseismic coupling model, which is converted from the slip deficit, shows that almost all 20 km of the uppermost MHT was locked during the interseismic period. It includes the coseismic slip region of the 2015 Nepal event. The seismic moment deficit is approximately 6.8×1019 Nm/yr, which is consistent with other studies.We compute the gravity changes at the Earth surface with a full wavelength on a 3’×3’ grid on the basis of the coseismic slip and interseismic slip deficit models. After considering the gravity change by vertical deformation, coseismic gravity change at the deformed surface has a dipolar distribution of gravity increase at the north of the epicenter and a decrease at the south. The magnitude of gravity change ranges from -261 μGal to 125 μGal and can be detected by traditional land gravimetry. The gravity change at Lhasa is -0.12 μGal, which was detected by using a superconductor gravimeter. Unlike the coseismic gravity change, the interseismic gravity change rate of the MHT after free air correction around the MHT ranges from -0.65 μGal/yr to 1.4 μGal/yr, which is difficult for gravimeters to detect with an accuracy of 10 μGal.We synthesize geoid, gravity, and gravity gradient tensor changes with long wavelengths caused by coseismic slip and interseismic slip deficit of the MHT by using spherical harmonic expansion of gravity changes. The truncation degrees of geoid and gravity are 60, and that of the gravity gradient tensor is 250, which is consistent with that of GRACE and of GOCE. In addition, similar to GRACE data post-process, geoid and gravity are smoothed by using a DDK3 filter, which is useful for damping the high-frequency noise. Gravity satellite is not sensitive to crustal vertical deformation; thus, gravity changes of the full wavelength without free air correction are used to expand into spherical harmonics. Results show that coseismic geoid and gravity changes with 60 degrees are distributed at the surface with a dipolar pattern. For the coseismic phase, the magnitude of geoid change is -0.2-0.3 mm, and that of gravity change is -0.9-1.2 μGal, which cannot be detected by GRACE with an observation accuracy of approximately 2 μGal. The synthetic interseismic geoid and gravity changes have an opposite pattern to the coseismic signals. The magnitudes of interseismic geoid and gravity are -0.026-0.014 mm/yr and -0.11-0.08 μGal/yr, respectively. The synthetic interseismic signals are much smaller than those values because of glacier melting on high mountains.The space coseismic gravity gradient of Trr has a dipolar pattern with a magnitude of -27-31 mE; components of Trθ and Tθθ have a tripolar pattern, and the magnitudes are -27-20 mE and -22-19 mE. The signals of the other three components are weaker at approximately ±10 mE. Unlike coseismic signals, all components of the interseismic gravity gradient tensor have a tripolar pattern in the range of -4-4 mE.Indubitably, gravity and gravity gradient changes with a low degree due to interseismic coupling of the MHT may not be detected by gravimetric satellite directly given their weaker signals compared with changes due to glacier mass migration or land water storage change. However, after careful correction for other sources, we can extract the gravity or gravity gradient change from next-generation gravimetric satellites, the measurement accuracy of which will be improved by new techniques such as laser ranging and an accurate gradiometer in the future.关键词：GPS;InSAR;gravity field;coseismic;interseismic;the Main Himalaya Thrust
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发布时间：2021-06-17 - 摘要：Crust stress is recognized as the vital force of solid earth hazards including earthquake, landslide and rock burst. The Curst Stress Field Altering (CSFA) in not only the source of solid earth hazards, but also the results of rock fracturing and earthquakes. The precursors of coming earthquake is essentially the particular appearance or the spatio-temporal projection of CSFA and the accumulated crust stress before shocking. Crust Stress Remote Sensing (CSRS) is a new paradigm of Remote Sensing, which can pave the way to making earthquake prediction possible. However, the traditional science and technology of remote sensing, which we call as Side-A of Remote Sensing, is theoretically based on the physical-chemical property of target and the radiation characteristics of surface conditions, without consideration to the additional radiation in condition of stress and fracturing. Present remote sensing physics has insufficient interpretation on the abnormal infrared-microwave radiation preceding earthquakes. As the theoretical foundation of CSRS and the new science and technology of remote sensing on additional radiation from stressed and fracturing solid, which we call as Side-B of Remote Sensing, it is urgently demanded to establish the physical mechanism of additional radiation from loaded rock and the quantitative technologies for separating additional electromagnetic radiation from noisy backgrounds. This paper briefly reviews international studies on infrared and microwave anomalies related to tectonic earthquakes. It also systematically establishes the achievements of electromagnetic radiation experimental observations in the domain of solid mechanics, which include thermal imaging analysis of material stress and damages, and the thermal image, thermal spectrum and microwave radiation observation on loaded rock to fracturing. The main achievements of studies on the mechanism of altering electromagnetic radiation from loaded rock to fracturing are also introduced. Such studies focus on (1) the rock physics mechanism including the effects of piezoelectric mineral crystals, discharging of crack tips, escaping of free electrons, and energy balance in an isolated system, (2) the quantum mechanics mechanism including the energy jump due to atom vibration and molecule rotation, and (3) the remote sensing physics mechanism including the effect of changing dielectric effect and changing surface emissivity. Referring to the coupling behaviors of multiple spheres of Earth system driven by CSFA, the principles and shortcomings of both the effect of battery transfer in crust rock and the effect of underground radon emission are also analyzed, and the multiple scale properties of Earth system response on seismogenic activities are finally presented. With regard to the Geophysical Satellites Plan in China, the key technologies are suggested, including the optimal selection of sensitive wave bands and its configuration for CSRS satellites, the remote sensing identification and combined diagnosis of tectonic activities and earthquake precursors, and the synergic observation with the use of spaceborne, airborne, and ground-based platforms on CSFA appearances as well as intelligent analysis.关键词：geophysics satellite;crust stress remote sensing (CSRS);crustal stress field alteration (CSFA);crustal stress responding;infrared brightness temperature;microwave brightness temperature;remote sensing rock mechanics (RSRM)
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发布时间：2021-06-17 - 摘要：China Seismo-Electromagnetic Satellite (CSES) is the first space-based electromagnetic platform of China’s stereo seismic monitoring system and the first satellite of China’s geophysical field exploration satellite program that will be used to obtain the in-situ structural parameters and their effects on Earth’s magnetic field, space electromagnetic wave field, and ionospheric plasma. According to the objective of CSES, the parameters of the satellite orbit, satellite platform, and payloads, including the satellite footprint, magnetic and charging cleanliness control and boom design, and the isoelectric potential on the platform surface, are analyzed and tested. On February 2, CSES was launched, and the commission test proved that the system works well. The entire team has overcome difficulties in the R&D phase. The platform and payload can work in orbit, and the preliminary test shows that the main function and performance meet the demand and index designed by the project.关键词：China Seismo-Electromagnetic Satellite (CSES);geophysical field;ionosphere;earthqueke;magnetic cleanliness;charging cleanliness;boom mechanism
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发布时间：2021-06-17 - 摘要：The critical technology of the Gravity Recovery And Climate Experiment (GRACE) satellite measures the change in the relative velocity between two low-orbit satellites. The static gravity field and the time variable gravity field can be estimated by the inter-satellite range-rate. Middle and high orders of gravity can obtain high accuracy. With practical consideration of the wide application of the time-variable gravity field, precise detection of related geophysical phenomena, such as ice sheets, ground water storage, and change in global sea level, is achieved provided that the measurement accuracy of the gravity satellite can be improved. Therefore, several research institutions have developed similar GRACE satellites before the original GRACE satellites crash. China is also stepping up research and development in this field.This paper discusses whether laser range measurement can improve the detection accuracy of the earth gravity field on the basis of the design of next-generation gravity satellites by using high-precision laser ranging technology instead of microwave ranging. A linearized inter-satellite range-rate formula is derived by using the high-precision dynamic gravity field model inversion method. Satellite orbital perturbation theory established the functional relationship between the observation of the two satellites in terms of the speed difference in the direction of the component with geopotential coefficients, the initial state parameters of the satellites, and the scale and bias parameters of an accelerometer. The function is linearized, and the linear equations of inter-satellite variation are obtained by discarding the smaller quantity above two orders.The normal equation is not solved if only the observed inter-satellite range-rate is used. When the two satellites after a previous one are used, the state transition matrix is almost the same, and the equation is rank-deficient. Therefore, the underdetermined equations can be solved with precise satellite orbit data. The observed precise satellite orbit data are sensitive only for a low order of the gravity field and have poor results at a high order; thus, we must find the best weight to combine the two types of data. Therefore, the inversion of the satellite gravity field based on the weight between precise orbit data with inter-satellite range-rate data is studied. It is solved for the precise satellite orbit data by using the dynamic method, which is linearized based on Newton’s second law of motion. The difference between the reference orbit and the actual satellite orbit is established with the state transfer matrix and parameter sensitivity matrix. The reference and actual orbits are calculated by using the eighth-order Adam method, and the initial orbit is calculated by the 10th-order Runge-Kutta method. The designed orbit parameter is the same as that of the GRACE satellite for easy comparison. The reference orbit uses the EGM96 model, and the actual orbit selects the EGM08 model. Each arc length is 6 hours, and its normal equation is established. One month of data are used for computation, and the establishment of the final normal equation is established by superpositioning the normal equations of all arcs. The matrix is computed by using the LU decomposition method. In Example 1, the KUALA curve shows that the calculation error with the error-free model is approximately five orders of magnitude smaller than the difference between the EGM96 and EGM08 gravity models, thereby confirming the accuracy of the program presented in this paper. Some simulation examples are calculated to analyze the effect of laser ranging on the accuracy of the Earth’s gravity field recovery. Simulation results show that when the accuracy of the inter-satellite range-rate is improved from 1.0×10-6 to 5.0×10-7, 1.0×10-7, 5.0×10-8, and 1.0×10-8 m/s, the accumulated geoid error at the 120th order is reduced from 85.14 cm to 33.09, 7.33, 3.70, and 3.59 cm. Therefore, the accuracy of the Earth’s static gravity field model, which is recovered by the satellite-to-satellite tracking in the low-low model, is expected to be one order of magnitude higher than that of GRACE after high-precision laser ranging. The KUALA curve shows that the static gravity field with the design accuracy of GRACE can be retrieved to the order of 90. However, when the accuracy of the inter-satellite range-rate is increased to 5.0×10-8 and 1.0×10-8 m/s, it can be completely recovered to the 120th order. The inter-satellite range-rate of 1.0×10-8 m/s has redundant measurement accuracy given that the two results are similar.Therefore, if the measurement accuracy of next-generation Chinese gravity satellites does not improve, then we recommend improving the accuracy of the inter-satellite range-rate to 5.0×10-8 m/s, thereby achieving a relevant breakthrough.关键词：laser ranging;static earth gravity field;geoid accuracy;SST-LL model;GRACE
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发布时间：2021-06-17 - 摘要：Interferometric Synthetic Aperture Radar (InSAR) has been proved to be a high-precision geodetic approach for monitoring the crustal deformation of the earth. Comparison with other methods, such as leveling, GPS, Very-Long-Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR) and so on, InSAR has the remarkable advantages of continuous large-area coverage and centimeter to millimeter-level measurement accuracy, its measuring results are the significant geophysical parameters needed by seismic research, thereby becoming an important means of seismic crustal deformation monitoring.The occurrence and development of earthquakes have periodic characteristics. A complete seismic cycle can be divided into four phases: pre-seismic, co-seismic, post-seismic and inter-seismic. Different seismic processes have their own crustal deformation characteristics, so we should to adopt different methods for the deformation monitoring at different stages. At present, D-InSAR technology is mainly used to monitor the co-seismic deformation, while time-series analysis of InSAR is in the inter-seismic deformation monitoring.In recent years, some new satellite platforms, namely, Sentinel-1A/1B RADARSAT-2, ALOS-2, TerraSAR/TanDEM-X and COSMO-SkyMed, have enhanced the ability to obtain SAR data globally with short revisit cycles and possibility for monitoring crustal deformations worldwide and routinely. In the meantime, the number of InSAR users, including governments, research institutes, and commercial companies, is expanding year by year, then the demands to improve the accuracy and reliability of InSAR results are also increasing.This paper first summarizes the landmark works and up-to-date research status of InSAR technology in seismic crustal deformation monitoring, then focuses on major limitations hindering the technique deeper applications, such as Atmospheric Phase Screen (APS), Line-Of-Sight (LOS) ambiguity, and imaged swath width. The existing methods to remove APS have been summarized, and an emerging method based on Numerical Weather Prediction (NWP) model has been discussed especially. The problems on swath width limitation and LOS ambiguity have been analyzed and the possible solutions are introduced. InSAR time-series analysis is an advanced method for monitoring inter-seismic and post-seismic displacement. In the paper, the most important four methods of InSAR time-series, which are PS-InSAR, SBAS, StaMPS, and SqueeSAR respectively, are described in detail.The paper concludes with a discussion of the key technical issues on InSAR applications and the associated ways toward to the solutions. The conclusions are given as follows: (1) APS is a main source of error in InSAR processing, which could be eliminated or mitigated by APS correction with the output from NWP models. (2) One-dimensional measurement along the LOS direction has greatly limited the capability of InSAR technique in the investigation of crustal deformations which demands three dimensional deformation components. To obtain accurate 3-D surface deformation not only need to incorporate descending InSAR result together with ascending one, or with Multi-Aperture Interferometry (MAI), but also SAR satellite in large oblique orbit should be considered. (3) High-coherence target selection is an important prerequisite for InSAR time series analysis. The problems, such as unevenly distribution of PS and low coherence of the natural surface, are main reasons for poor performance of InSAR time-series analysis application in Earthquake research. Reasonable choice of the thresholds and optimal high-coherence target selection strategies can improve the accuracy of InSAR results. (4) Wide area mapping is urgently needed in the crustal deformation monitoring, since the coverage of the great earthquakes faults usually extended over several hundreds or even up to thousands kilometers. Strategies to merge multi-track InSAR results together with ScanSAR interferometry and its time series analysis should be took into consideration in future. (5) Time-series analysis algorithms must be adapted to incorporate each new image in an efficient and optimal manner without starting the processing from scratch. New approaches should be proposed as efficient processing schemes to exploit the unprecedented Big Data for high-precision near-real-time processing. (6) Now the validation of InSAR outputs or its accuracy estimation relies heavily on GPS, leveling, and other external data. Here, we propose an idea to introduce the “Totally Quality Control” into InSAR processing chain that goes through every step of InSAR time series processing to indentify the possible artifacts in the processing and correcting them to ensure the quality of the outputs.关键词：seismic crustal deformation;InSAR;D-InSAR;time series;ScanSAR
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发布时间：2021-06-17 - 摘要：Remote sensing technology has become an important technique of active fault research because of its macro, intuitive and non-contact advantages. With the rapid development of remote sensing technology, the increasement of satellite sensors and the improvement of spatial resolution, a various data of satellite sensors at home and abroad have been widely used in active fault research. Foreign satellite data mainly include ALOS, IKONOS, SPOT, QuickBird, Worldview and so on, among which the spatial resolution of QuickBird is 0.6 m, Worldview up to 0.31 m. Domestic satellite data include GF-1, GF-2 and ZY3, where the spatial resolution of GF-1 multispectral band and panchromatic band is 8 m and 2 m respectively; the spatial resolution of ZY3 multispectral band and panchromatic band is 5.8 m and 2.1 m respectively; the spatial resolution of GF-2 multispectral band and panchromatic band is 4 m and 1 m respectively.In recent decades, the rapid development of urbanization and human activities have seriously destroyed natural landforms. Especially in the eastern part of China, natural landforms have been seriously damaged due to the construction of roads, railways, factories and houses, so that tectonic geomorphology no longer existed, which made a great difficulty for remote sensing interpretation of active tectonics. US Keyhole(KH) satellites began to run in the 1960s, taking a large number of images in China. KH images are characterized by early imaging time, high resolution and better original terrain information, so they can be effective to obtain the characteristics of tectonic geomorphology and determine the geometric distribution and fault behavior. Those are significant for active fault research.In this paper, the basic information and data processing flow of KH satellite is introduced firstly. KH satellite mainly include KH1-12 and other 12 models. KH1-6 is the recoverable reconnaissance satellite of photographic film. The data source of KH1-6 is basically open, which is the main application of the promotion model. The best resolution of KH4A, KH4B and KH6 is 2.7 m, 1.8 m and 0.3 m respectively. Secondly, the application of KH images in active fault is discussed: 1) For the tectonic landform of active fault, with the advantages of early imaging time and high resolution, KH images can obtain the tectonic micro- landform features of active fault such as linear structure, fault scarp, fault cliff, fault groove and channels offset, which can not be identified by current satellite images. They are helpful to complete the precision mapping and quantitative analysis of active fault; 2) For the surface rupture zone of a historical earthquake, the KH images photographed at the nearest time after the earthquake is useful to map the surface rupture of the earthquake and measure the coseismic displacement. KH images visualize the post-earthquake rupture information to reveal the relationship between the rupture and the active fault, which guides us to understand the seismogenic structure, seismogenic mechanism and the process of diastrophism. Finally, this paper take the Jiangsu section of the Tan-Lu Fault Zone(TLFZ) as an example. The Suqian city and surrounding area were selected as the test area, where the remote sensing interpretation of the active fault based on KH-4B satellite image was carried out. The results show that, Malingshan-Chonggangshan Fault(F5) and Xinyi-Xindian Fault (F2) intermittently exposed to the surface. The tectonic micro-landforms of the two faults are very developed. In the Huangchaoguan, Shanxiawu and the south of Xiaodian, F5 exposed to the surface, which formed fault cliff, fault triangular surface, fault scarp and other structural landform. In the west of Huangchaoguan, F2 intermittent exposed to the surface, which formed fault scarp, fault deflection, fault groove and other tectonic micro-landforms. There are no obvious dislocations in the gully of the two faults. The two faults are mainly dip-slip movement with high angle thrust motion.KH satellites have obtained a large number of instantaneous image data from the last century, and recorded the process and evolution of the Earth's surface for a period of time. These images have important application values in the field of active fault research. In order to study and understand the geological structure, tectonic landforms and the latest historical changes, the KH images provide more accurate basic data. How applying KH images to active fault mapping work and seismic hazard assessment is an important development direction in active tectonics research in the future. What is more, It is hoped that, except in the earthquake industry, KH satellite data will be widely used in the fields of forestry, fishery, surveying and mapping, engineering, electric power, and other industries.关键词：KH images;active fault;Jiangsu segment of Tan-Lu fault zone;tectonic micro-landform
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发布时间：2021-06-17 - 摘要：The application of seismic remote sensing in China began in mid 1970s. More than 40 years have passed since the beginning of the simple linear active structure of multi spectral image interpretation. In the 1970s and 1980s, it was characterized by the application of visible light remote sensing images, and in the 1990s, the infrared remote sensing, GNSS remote sensing, and InSAR technology were at the experimental application stage. From the late 20th century to the first decade of the 21st century, it was mainly manifested as integrated remote sensing application and pre-research of the satellite program of geophysical field exploration, such as electromagnetic field and gravity satellites. Since 2011, more attentions were played to integrating previous research results, implementing the geophysical field satellite plan, and the constructing, as well as operating the satellite seismic application system. After more than 40 years of development, the application of visible-light remote sensing technology in active tectonic exploration and disaster assessment has been realized. Satellite infrared, satellite electromagnetism, InSAR technology, satellite gravity, and hyperspectral gas geochemical detection technology have become increasingly prominent in the field of seismic monitoring. As the first satellite of the national geophysical field exploration satellite program, China Seismic-Electromagnetic Satellite, named ZH-1, entered its present orbit on February 2, 2018. At present, China’s first global geomagnetic map was produced after the normal operation in orbit, which fills the gap in the acquisition capacity of the global geophysical field in China.关键词：seismic remote sensing;geophysical field detection satellites;satellite electromagnetic;satellite gravity;InSAR;infrared remote sensing;optical remote sensing;GNSS remote sensingremote sensing
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发布时间：2021-06-17
- Postal code：100190
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