Conventional Synthetic Aperture Radar (SAR) systems cannot obtain high-resolution and wide-swath illumination area due to the well-known minimum antenna area constraint. Single Phase Center MultiBeam (SPCMB) technique...Conventional Synthetic Aperture Radar (SAR) systems cannot obtain high-resolution and wide-swath illumination area due to the well-known minimum antenna area constraint. Single Phase Center MultiBeam (SPCMB) technique can overcome this limitation by adding spatial sampling through multiple receivers in azimuth direction. Unfortunately, this approach will lead to an increase of azimuth ambiguities (interbeam ambiguities), because each receive beam’s mainlobe overlaps with the other ones’ sidelobes. This paper proves that the front part of SPCMB SAR systems can be considered to be a hybrid filterbank. Therefore, the azimuth signal can be reconstructed and the interbeam am- biguities can be effectively suppressed by a well-designed hybrid filterbank.展开更多
High acceleration of radar targets is analyzed using Acceleration Ambiguity Function (AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are deriva...High acceleration of radar targets is analyzed using Acceleration Ambiguity Function (AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.展开更多
It is a main form using the main beamwidth of the ambiguity function to judge the signal resolution, in which the range or Doppler resolution of the signals are investigated for the targets close to each other. Howeve...It is a main form using the main beamwidth of the ambiguity function to judge the signal resolution, in which the range or Doppler resolution of the signals are investigated for the targets close to each other. However, for the pulse signal with rectangular envelope, if the nominal range resolution is calculated from the classic definition, there exists the problem of infinite integral for the high power terms of sine function, and a definite result could not be obtained. Though a definite solution of the nominal velocity resolution can be calculated from the definition, the calculation for the signal consisting of multiple-pulse, especially several periods, is very complex. The paper begins with the physical meaning of nominal resolution rather than from the definition formula to solve the problem using the ambiguity matrix, and make the calculation simplified greatly.展开更多
In this paper, an electrical resistance tomography(ERT) imaging method is used as a classifier, and then the Dempster-Shafer's evidence theory with fuzzy clustering is integrated to improve the ERT image quality. ...In this paper, an electrical resistance tomography(ERT) imaging method is used as a classifier, and then the Dempster-Shafer's evidence theory with fuzzy clustering is integrated to improve the ERT image quality. The fuzzy clustering is applied to determining the key mass function, and dealing with the uncertain, incomplete and inconsistent measured imaging data in ERT. The proposed method was applied to images with the same investigated object under eight typical current drive patterns. Experiments were performed on a group of simulations using COMSOL Multiphysics tool and measurements with a piece of porcine lung and a pair of porcine kidneys as test materials. Compared with any single drive pattern, the proposed method can provide images with a spatial resolution of about 10% higher, while the time resolution was almost the same.展开更多
Due to the almost homogeneous topography in low relief areas, it is usually difficult to make accurate predictions of soil properties using topographic covariates. In this study, we examined how time series of field s...Due to the almost homogeneous topography in low relief areas, it is usually difficult to make accurate predictions of soil properties using topographic covariates. In this study, we examined how time series of field soil moisture observations can be used to estimate soil texture in an oasis agricultural area with low relief in the semi-arid region of northwest China. Time series of field-observed soil moisture variations were recorded for 132 h beginning at the end of an irrigation event during which the surface soil was saturated.Spatial correlation between two time-adjacent soil moisture conditions was used to select the factors for fuzzy c-means clustering. In each of the ten generated clusters, soil texture of the soil sample with the maximum fuzzy membership value was taken as the cluster centroid. Finally, a linearly weighted average was used to predict soil texture from the centroids. The results showed that soil moisture increased with the increase of clay and silt contents, but decreased with the increase of sand content. The spatial patterns of soil moisture changed during the entire soil drying phase. We assumed that these changes were mainly caused by spatial heterogeneity of soil texture. A total of 64 independent samples were used to evaluate the prediction accuracy. The root mean square error(RMSE)values of clay, silt and sand were 1.63, 2.81 and 3.71, respectively. The mean relative error(RE) values were 9.57% for clay, 3.77% for silt and 12.83% for sand. It could be concluded that the method used in this study was effective for soil texture mapping in the low-relief oasis agricultural area and could be applicable in other similar irrigation agricultural areas.展开更多
文摘Conventional Synthetic Aperture Radar (SAR) systems cannot obtain high-resolution and wide-swath illumination area due to the well-known minimum antenna area constraint. Single Phase Center MultiBeam (SPCMB) technique can overcome this limitation by adding spatial sampling through multiple receivers in azimuth direction. Unfortunately, this approach will lead to an increase of azimuth ambiguities (interbeam ambiguities), because each receive beam’s mainlobe overlaps with the other ones’ sidelobes. This paper proves that the front part of SPCMB SAR systems can be considered to be a hybrid filterbank. Therefore, the azimuth signal can be reconstructed and the interbeam am- biguities can be effectively suppressed by a well-designed hybrid filterbank.
文摘High acceleration of radar targets is analyzed using Acceleration Ambiguity Function (AAF). The acceleration resolution based on AAF is defined. The AAF and acceleration resolution of rectangle pulse signal are derivated and the conclusion that its acceleration resolution is in inverse proportion with the square of its duration is drawn. In the end, these conclusions are applied to the parameter designing and performance evaluation for a certain type of pulse Doppler radar.
基金Supported by the National Natural Science Foundation of China(No.60232010)
文摘It is a main form using the main beamwidth of the ambiguity function to judge the signal resolution, in which the range or Doppler resolution of the signals are investigated for the targets close to each other. However, for the pulse signal with rectangular envelope, if the nominal range resolution is calculated from the classic definition, there exists the problem of infinite integral for the high power terms of sine function, and a definite result could not be obtained. Though a definite solution of the nominal velocity resolution can be calculated from the definition, the calculation for the signal consisting of multiple-pulse, especially several periods, is very complex. The paper begins with the physical meaning of nominal resolution rather than from the definition formula to solve the problem using the ambiguity matrix, and make the calculation simplified greatly.
基金Supported by National Natural Science Foundation of China(No.61774014 and No.60772080)
文摘In this paper, an electrical resistance tomography(ERT) imaging method is used as a classifier, and then the Dempster-Shafer's evidence theory with fuzzy clustering is integrated to improve the ERT image quality. The fuzzy clustering is applied to determining the key mass function, and dealing with the uncertain, incomplete and inconsistent measured imaging data in ERT. The proposed method was applied to images with the same investigated object under eight typical current drive patterns. Experiments were performed on a group of simulations using COMSOL Multiphysics tool and measurements with a piece of porcine lung and a pair of porcine kidneys as test materials. Compared with any single drive pattern, the proposed method can provide images with a spatial resolution of about 10% higher, while the time resolution was almost the same.
基金supported by the National Natural Science Foundation of China(Nos.41130530,91325301,41201207 and 41571212)the Project of Frontier Fields during the Thirteenth Five-Year Plan Period of the Institute of Soil Science,Chinese Academy of Sciences(ISSASIP1622)
文摘Due to the almost homogeneous topography in low relief areas, it is usually difficult to make accurate predictions of soil properties using topographic covariates. In this study, we examined how time series of field soil moisture observations can be used to estimate soil texture in an oasis agricultural area with low relief in the semi-arid region of northwest China. Time series of field-observed soil moisture variations were recorded for 132 h beginning at the end of an irrigation event during which the surface soil was saturated.Spatial correlation between two time-adjacent soil moisture conditions was used to select the factors for fuzzy c-means clustering. In each of the ten generated clusters, soil texture of the soil sample with the maximum fuzzy membership value was taken as the cluster centroid. Finally, a linearly weighted average was used to predict soil texture from the centroids. The results showed that soil moisture increased with the increase of clay and silt contents, but decreased with the increase of sand content. The spatial patterns of soil moisture changed during the entire soil drying phase. We assumed that these changes were mainly caused by spatial heterogeneity of soil texture. A total of 64 independent samples were used to evaluate the prediction accuracy. The root mean square error(RMSE)values of clay, silt and sand were 1.63, 2.81 and 3.71, respectively. The mean relative error(RE) values were 9.57% for clay, 3.77% for silt and 12.83% for sand. It could be concluded that the method used in this study was effective for soil texture mapping in the low-relief oasis agricultural area and could be applicable in other similar irrigation agricultural areas.
