Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601530
R. Persico, F. Soldovieri, I. Catapano, G. Pochanin, V. Ruban, O. Orlenko
The capabilities of a microwave inverse scattering algorithm for GPR data processing are tested against experimental data gathered by means of a prototypical GPR system. The approach is based on the Born approximation (BA) and exploits a differential contactless measurement configuration. Accordingly, the data are obtained as the difference of the electrical fields gathered at two symmetrical positions with respect to the source location. The use of the differential configuration allows to reduce substantially the mutual direct coupling between the transmitting and receiving parts of the antenna system and this makes it possible to increase power budget of the GPR system.
{"title":"Experimental results of a microwave tomography approach applied to a differential measurement configuration","authors":"R. Persico, F. Soldovieri, I. Catapano, G. Pochanin, V. Ruban, O. Orlenko","doi":"10.1109/IWAGPR.2013.6601530","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601530","url":null,"abstract":"The capabilities of a microwave inverse scattering algorithm for GPR data processing are tested against experimental data gathered by means of a prototypical GPR system. The approach is based on the Born approximation (BA) and exploits a differential contactless measurement configuration. Accordingly, the data are obtained as the difference of the electrical fields gathered at two symmetrical positions with respect to the source location. The use of the differential configuration allows to reduce substantially the mutual direct coupling between the transmitting and receiving parts of the antenna system and this makes it possible to increase power budget of the GPR system.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132959164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601512
C. Ferrara, P. M. Barone, E. Mattei, A. Galli, D. Comite, S. Lauro, G. Vannaroni, E. Pettinelli
In the present paper we use the recently-proposed early-time GPR (Ground Penetrating Radar) amplitude technique with the aim of detecting the variations of electric conductivity in a porous material having a uniform permittivity. A specific laboratory setup has been realised to evaluate the sensitivity of the early-time amplitudes to the variations of the subsurface salt concentration (i.e., conductivity). To assess the capacity of the early-time amplitude to follow the electrical conductivity changes, we compare the early-time results acquired using the envelope of the first part of GPR signals with the concurrent conductivity measured with TDR (Time Domain Reflectometry). The GPR survey has been carried out using a bistatic radar unit (Sensors & Software, Inc) operating at 1 GHz. Further useful information has been derived by suitably implementing a full-wave numerical modelling, able to accurately analyse the features of the waves detected by the GPR with flexible parameterization. Our results indicate that the near-surface electromagnetic properties of the material can be directly extracted from the GPR early-time amplitude technique. In particular, both experimental and numerical data show a very high correlation coefficient between the radar signal amplitude and the TDR-derived electrical conductivities.
{"title":"An evaluation of the early-time GPR amplitude technique for electrical conductivity monitoring","authors":"C. Ferrara, P. M. Barone, E. Mattei, A. Galli, D. Comite, S. Lauro, G. Vannaroni, E. Pettinelli","doi":"10.1109/IWAGPR.2013.6601512","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601512","url":null,"abstract":"In the present paper we use the recently-proposed early-time GPR (Ground Penetrating Radar) amplitude technique with the aim of detecting the variations of electric conductivity in a porous material having a uniform permittivity. A specific laboratory setup has been realised to evaluate the sensitivity of the early-time amplitudes to the variations of the subsurface salt concentration (i.e., conductivity). To assess the capacity of the early-time amplitude to follow the electrical conductivity changes, we compare the early-time results acquired using the envelope of the first part of GPR signals with the concurrent conductivity measured with TDR (Time Domain Reflectometry). The GPR survey has been carried out using a bistatic radar unit (Sensors & Software, Inc) operating at 1 GHz. Further useful information has been derived by suitably implementing a full-wave numerical modelling, able to accurately analyse the features of the waves detected by the GPR with flexible parameterization. Our results indicate that the near-surface electromagnetic properties of the material can be directly extracted from the GPR early-time amplitude technique. In particular, both experimental and numerical data show a very high correlation coefficient between the radar signal amplitude and the TDR-derived electrical conductivities.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114215596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601537
A. Strange
In GPR applications where the antenna is subject to fast movement, vibration or rapid changes in the surface properties, it is desirable to decrease the time required to acquire a complete time domain trace to prevent the distortion of subsurface features between traces. One survey practice that can be adopted to minimize this effect is to decrease the number samples per trace during acquisition. This approach, however, decreases the precision of quantitative subsurface layer thickness measurements due to the timing uncertainty between samples. One processing method that can be applied to increase the measurement precision is interpolation along the time axis. Experiments were conducted to quantify the performance of two interpolation methods in which scans were acquired with both low and high number of samples per trace. The low resolution scans were interpolated to match the number of samples of the high resolution traces. The results show that there is a reduction in the target range error when interpolating along the time axis to increase the sampling resolution.
{"title":"Analysis of time interpolation for enhanced resolution GPR data","authors":"A. Strange","doi":"10.1109/IWAGPR.2013.6601537","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601537","url":null,"abstract":"In GPR applications where the antenna is subject to fast movement, vibration or rapid changes in the surface properties, it is desirable to decrease the time required to acquire a complete time domain trace to prevent the distortion of subsurface features between traces. One survey practice that can be adopted to minimize this effect is to decrease the number samples per trace during acquisition. This approach, however, decreases the precision of quantitative subsurface layer thickness measurements due to the timing uncertainty between samples. One processing method that can be applied to increase the measurement precision is interpolation along the time axis. Experiments were conducted to quantify the performance of two interpolation methods in which scans were acquired with both low and high number of samples per trace. The low resolution scans were interpolated to match the number of samples of the high resolution traces. The results show that there is a reduction in the target range error when interpolating along the time axis to increase the sampling resolution.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133874536","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601514
N. Allroggen, J. Tronicke, Marcel Delock, Urs Boniger
The topographic relief of a typical ground-penetrating radar (GPR) survey can easily be in the range of the target depth. In complex subsurface settings, this requires the application of topographic migration schemes to reliably image subsurface structures. Furthermore, a shallow ground water layer introduces significant vertical variations in GPR propagation velocity, which should be considered during migration to accurately image subsurface structures. In this paper, we present a modified topographic migration scheme, which is able to account for vertical variable velocities by using the root-mean-square (rms) velocity approximation. We evaluate our migration scheme by using synthetic and field data, which represent typical near-surface sedimentary structures often investigated using GPR. These examples demonstrate that a significant improvement in structural imaging quality is achieved by considering rms velocities during topographic migration.
{"title":"Topographic migration of GPR data with variable velocities","authors":"N. Allroggen, J. Tronicke, Marcel Delock, Urs Boniger","doi":"10.1109/IWAGPR.2013.6601514","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601514","url":null,"abstract":"The topographic relief of a typical ground-penetrating radar (GPR) survey can easily be in the range of the target depth. In complex subsurface settings, this requires the application of topographic migration schemes to reliably image subsurface structures. Furthermore, a shallow ground water layer introduces significant vertical variations in GPR propagation velocity, which should be considered during migration to accurately image subsurface structures. In this paper, we present a modified topographic migration scheme, which is able to account for vertical variable velocities by using the root-mean-square (rms) velocity approximation. We evaluate our migration scheme by using synthetic and field data, which represent typical near-surface sedimentary structures often investigated using GPR. These examples demonstrate that a significant improvement in structural imaging quality is achieved by considering rms velocities during topographic migration.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121829489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601548
A. Zhuravlev, S. Ivashov, V. Razevig, I. Vasiliev, A. Bugaev
This paper describes the implementation of a holographic subsurface radar for sounding at shallow depths. The radar uses continuous signal with frequency switching and records phases of reflected signal at several operating frequencies. Two versions of the radar with frequency bandwidths 6.4-6.8 and 13.8-14.6 GHz were designed and tested. The data acquisition is accomplished by manual scanning along parallel equidistant lines. Upon acquisition, this two-dimensional interference pattern, or hologram, can be focused by the outlined Fourier-based back propagation algorithm into an image that reflects distribution of sources. Experimentally obtained and demonstrated in the paper images with plan view resolution of the order of 1 cm suggest application of the radar in civil engineering and non-destructive testing.
{"title":"Holographic subsurface radar RASCAN-5","authors":"A. Zhuravlev, S. Ivashov, V. Razevig, I. Vasiliev, A. Bugaev","doi":"10.1109/IWAGPR.2013.6601548","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601548","url":null,"abstract":"This paper describes the implementation of a holographic subsurface radar for sounding at shallow depths. The radar uses continuous signal with frequency switching and records phases of reflected signal at several operating frequencies. Two versions of the radar with frequency bandwidths 6.4-6.8 and 13.8-14.6 GHz were designed and tested. The data acquisition is accomplished by manual scanning along parallel equidistant lines. Upon acquisition, this two-dimensional interference pattern, or hologram, can be focused by the outlined Fourier-based back propagation algorithm into an image that reflects distribution of sources. Experimentally obtained and demonstrated in the paper images with plan view resolution of the order of 1 cm suggest application of the radar in civil engineering and non-destructive testing.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123599189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601547
Shiping Zhu, Jian Wang, Yi Su, Motoyuki Sato
A circular survey for 3D GPR using the linearly polarized antenna is proposed to detect and map the hidden cylinders. The backscattering signal from cylinders may strongly depend on the orientation of the cylinder relative to the antenna. The circular survey can conform to the optimal measuring condition that the long axis of the bow-tie antenna oriented is parallel to the long axis of the cylinders, and always obtain the strongest reflected signal from the cylinders. A regular survey and a circular survey using 3D GPR were carried out in the sand pit, and two crossing metal pipes were buried in dry sand as the targets. The compare results show the advantage and potential of the circular survey to detect the cylinders with the different orientations simultaneously. The fusion of the migrated result and the locations of the detected hyperbolic apices can provide more accurate mapping result of two pipes in accordance with the true scene.
{"title":"A circular survey for 3D ground penetrating radar to map hidden cylinders","authors":"Shiping Zhu, Jian Wang, Yi Su, Motoyuki Sato","doi":"10.1109/IWAGPR.2013.6601547","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601547","url":null,"abstract":"A circular survey for 3D GPR using the linearly polarized antenna is proposed to detect and map the hidden cylinders. The backscattering signal from cylinders may strongly depend on the orientation of the cylinder relative to the antenna. The circular survey can conform to the optimal measuring condition that the long axis of the bow-tie antenna oriented is parallel to the long axis of the cylinders, and always obtain the strongest reflected signal from the cylinders. A regular survey and a circular survey using 3D GPR were carried out in the sand pit, and two crossing metal pipes were buried in dry sand as the targets. The compare results show the advantage and potential of the circular survey to detect the cylinders with the different orientations simultaneously. The fusion of the migrated result and the locations of the detected hyperbolic apices can provide more accurate mapping result of two pipes in accordance with the true scene.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124686198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601531
R. Persico, G. Leucci, F. Soldovieri
This paper deals with the “mathematical description'” of the shape of the GPR diffraction curve in dependence of the distance of the measurement line from to the air/soil interface. In this relevant case., the diffraction curve relative to point-like target is mathematically expressed in a closed form by means of the solution of a fourth degree algebraic equation and this simplifies the analysis of the different measurement factors.
{"title":"The effect of the height of the GPR antennas on the diffraction curve","authors":"R. Persico, G. Leucci, F. Soldovieri","doi":"10.1109/IWAGPR.2013.6601531","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601531","url":null,"abstract":"This paper deals with the “mathematical description'” of the shape of the GPR diffraction curve in dependence of the distance of the measurement line from to the air/soil interface. In this relevant case., the diffraction curve relative to point-like target is mathematically expressed in a closed form by means of the solution of a fourth degree algebraic equation and this simplifies the analysis of the different measurement factors.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"352 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125631406","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601506
K. Chahine, V. Baltazart, Yide Wang
Linear prediction methods, based on a Hankel data matrix, suffer from subspace leakage and degraded resolution when applied to data models that do not result in a mode matrix with Vandermonde structure, such as the constant-Q model. In the absence of noise, the Vandermonde structure ensures the equivalence between the number of backscattered signals and the rank of the data matrix. This paper first identifies the origin of subspace leakage residing in linear prediction methods when applied to data of the constant-Q model. Then it proposes a frequency-distortion technique, based on the extension theorems, for suppressing this leakage and preserving the time resolution performance of subspace-based and linear prediction data processing methods.
{"title":"A subspace leakage suppression technique for high resolution processing of dispersive GPR signals","authors":"K. Chahine, V. Baltazart, Yide Wang","doi":"10.1109/IWAGPR.2013.6601506","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601506","url":null,"abstract":"Linear prediction methods, based on a Hankel data matrix, suffer from subspace leakage and degraded resolution when applied to data models that do not result in a mode matrix with Vandermonde structure, such as the constant-Q model. In the absence of noise, the Vandermonde structure ensures the equivalence between the number of backscattered signals and the rank of the data matrix. This paper first identifies the origin of subspace leakage residing in linear prediction methods when applied to data of the constant-Q model. Then it proposes a frequency-distortion technique, based on the extension theorems, for suppressing this leakage and preserving the time resolution performance of subspace-based and linear prediction data processing methods.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127126505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601543
Jian Wang, Shiping Zhu, Yi Su
The bow-tie antenna, which is widely used in impulse ground penetrating radar (GPR), has very low radiating efficiency. It is because that, nearly 70% of the radiated energy exists as the form of end reflection, which is harmful to probe objects. In order to keep the probing ability, the remarkable energy in end reflections is usually dissipated by resistive loading. We find that, in this paper, if the exciting pulse is bipolar and monocycle, the radiation efficiency can be significantly improved by utilizing the energy in end reflection. And the improvement can be implemented by optimizing the antenna length. The proposed method is validated by simulated experiment. And the results show that, the radiation efficiency can be increased by 100% compared with an antenna with infinite length. Additionally, the proposed method is easy to be carried out in applications and of great use.
{"title":"Use end reflections to improve the radiation efficiency of bow-tie antenna","authors":"Jian Wang, Shiping Zhu, Yi Su","doi":"10.1109/IWAGPR.2013.6601543","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601543","url":null,"abstract":"The bow-tie antenna, which is widely used in impulse ground penetrating radar (GPR), has very low radiating efficiency. It is because that, nearly 70% of the radiated energy exists as the form of end reflection, which is harmful to probe objects. In order to keep the probing ability, the remarkable energy in end reflections is usually dissipated by resistive loading. We find that, in this paper, if the exciting pulse is bipolar and monocycle, the radiation efficiency can be significantly improved by utilizing the energy in end reflection. And the improvement can be implemented by optimizing the antenna length. The proposed method is validated by simulated experiment. And the results show that, the radiation efficiency can be increased by 100% compared with an antenna with infinite length. Additionally, the proposed method is easy to be carried out in applications and of great use.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117051772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-07-02DOI: 10.1109/IWAGPR.2013.6601536
L. Anishchenko, S. Ivashov, I. Catapano, L. Crocco, G. Gennarelli, F. Soldovieri
This paper deals with the exploitation of two bio-radar systems (4 GHz and 14 GHZ frequency) developed at Remote Sensing Laboratory of the Bauman Moscow State Technical University for vital signs characterization (breathing and heartbeat). In particular, an experiment has been performed with the two radar systems, in order to appraise the different performance, in terms of detection and accuracy, with respect to vital signs estimation. For this experiment, the data have been processed by means of a recently developed approach that allows us to perform the parameter estimation (and therefore the overall monitoring process) in an automatic way.
{"title":"Radar for vital signs characterization: A comparison between two different frequency band systems","authors":"L. Anishchenko, S. Ivashov, I. Catapano, L. Crocco, G. Gennarelli, F. Soldovieri","doi":"10.1109/IWAGPR.2013.6601536","DOIUrl":"https://doi.org/10.1109/IWAGPR.2013.6601536","url":null,"abstract":"This paper deals with the exploitation of two bio-radar systems (4 GHz and 14 GHZ frequency) developed at Remote Sensing Laboratory of the Bauman Moscow State Technical University for vital signs characterization (breathing and heartbeat). In particular, an experiment has been performed with the two radar systems, in order to appraise the different performance, in terms of detection and accuracy, with respect to vital signs estimation. For this experiment, the data have been processed by means of a recently developed approach that allows us to perform the parameter estimation (and therefore the overall monitoring process) in an automatic way.","PeriodicalId":257117,"journal":{"name":"2013 7th International Workshop on Advanced Ground Penetrating Radar","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2013-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122679137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：