The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third...The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.展开更多
Downward Looking Sparse Linear Array Three Dimensional SAR(DLSLA 3D SAR) is an important form of 3D SAR imaging, which has a widespread application field. Since its practical equivalent phase centers are usually distr...Downward Looking Sparse Linear Array Three Dimensional SAR(DLSLA 3D SAR) is an important form of 3D SAR imaging, which has a widespread application field. Since its practical equivalent phase centers are usually distributed sparsely and nonuniformly, traditional 3D SAR algorithms suffer from low resolution and high sidelobes in cross-track dimension. To deal with this problem, this paper introduces a method based on back-projection and convex optimization to achieve 3D high accuracy imaging reconstruction. Compared with traditional SAR algorithms, the proposed method sufficiently utilizes the sparsity of the 3D SAR imaging scene and can achieve lower sidelobes and higher resolution in cross-track dimension. In the simulated experiments, the reconstructed results of both simple and complex imaging scene verify that the proposed method outperforms 3D back-projection algorithm and shows satisfying cross-track dimensional resolution and good robustness to noise.展开更多
The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-...The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.展开更多
In this paper a new spherical actuator is designed and its advantages are compared to an existing spherical actuator, which function is limited by several design bottlenecks. First the output torque is too small. Seco...In this paper a new spherical actuator is designed and its advantages are compared to an existing spherical actuator, which function is limited by several design bottlenecks. First the output torque is too small. Second, the attitude is difficult to be accurately detected. The new three-dimen- sional magnetic pole array can solve these major problems. The new actuator features an outer rotor with multiple permanent magnet （PM） poles. Using an analytical solution and the finite element so- lution simulation, the feasibility of the approach is verified. A prototype was developed, tested, and experiments were conducted to obtain the practical value of the magnetic flux density.展开更多
As a 3-D display technology,stereoscopic imaging with lenticular lens sheet can only offer viewers the horizontal parallax.To reconstruct the 3-D image with parallax in both horizontal and vertical directions,the full...As a 3-D display technology,stereoscopic imaging with lenticular lens sheet can only offer viewers the horizontal parallax.To reconstruct the 3-D image with parallax in both horizontal and vertical directions,the full parallax technique with micro-lens array was proposed.But due to the fabrication constraints and cost concerns of the micro-lens array,application of the full parallax technique is restricted in practice.In this paper we revisited the lenticular sheet method and cross-lenticular lens array formed by two lenticular sheets overlapped orthogonally.By analyzing the optical properties of this cross-lenticular lens array,we found that it has reasonable imaging qualities as a conventional micro-lens array.Besides,due to the poor optical property of the outskirt area of the cross-lenticular lens,the cross-lenticular lens array has better crosstalk suppression capability than the conventional one.Based on the analysis,in this paper,we used the proposed lens array to reconstruct a 3-D image and verified its practicability.The cross-lenticular lens array was found feasible to take the full parallax technique into commercial applications,with comparable advantages in terms of low-cost and easy fabrication over a large area.展开更多
On 22 nd May 2021(local time),an earthquake of M_(s)7.4 struck Maduo county in Qinghai Province,China.This was the largest earthquake in China since the 2008 Wenchuan earthquake.In this study,ascending/descending Sent...On 22 nd May 2021(local time),an earthquake of M_(s)7.4 struck Maduo county in Qinghai Province,China.This was the largest earthquake in China since the 2008 Wenchuan earthquake.In this study,ascending/descending Sentinel-1 and advanced land observation satellite-2(ALOS-2)synthetic aperture radar(SAR)images were used to derive the three-dimensional(3-D)coseismic displacements of this earthquake.We used the differential interferometric SAR(In SAR,DIn SAR),pixel offset-tracking(POT),multiple aperture In SAR(MAI),and burst overlap interferometry(BOI)methods to derive the displacement observations along the line-of-sight(LOS)and azimuth directions.To accurately mitigate the effect of ionospheric delay on the ALOS-2 DIn SAR observations,a polynomial fitting method was proposed to optimize range-spectrum-split-derived ionospheric phases.In addition,the 3-D displacement field was obtained by a strain model and variance component estimation(SM-VCE)method based on the high-quality SAR displacement observations.Results indicated that a left-lateral fault slip with the largest horizontal displacement of up to 2.4 m dominated this earthquake,and the small-magnitude vertical displacement with an alternating uplift/subsidence pattern along the fault trace was more concentrated in the near-fault regions.Comparison with the global navigation satellite system data indicated that the SM-VCE method can significantly improve the accuracy of the displacements compared to the classical weighted least squares method,and the incorporation of the BOI displacements can substantially benefit the accuracy of north-south displacement.In addition to the displacements,three coseismic strain invariants calculated based on the strain model parameters were also investigated.It was found that the eastern and western parts of the faults suffered more significant strains compared with the epicenter region.展开更多
To obtain high cross-range resolution, the underwater 3-D acoustic imaging system usually requires a rectangular array with a great number of sensors and a large physical size. To reduce the sensor number and the arra...To obtain high cross-range resolution, the underwater 3-D acoustic imaging system usually requires a rectangular array with a great number of sensors and a large physical size. To reduce the sensor number and the array physical size simultaneously, this paper proposes a new underwater 3-D acoustic imaging approach based on a novel multiple-input multiple-output (MIMO) array. Specifically, the MIMO array is composed of four uniform linear arrays (ULAs) located on four sides of a rectangle. The transmitting array composed of two ULAs is located on a pair of opposite sides, and the receiving array composed of another two ULAs is located on the other two sides. Furthermore, narrowband waveforms coded with orthogonal polyphase sequences are employed as transmitting waveforms. When the subcode numbers in the polyphase coded sequences are sufficient, the MIMO array has the same 3-D imaging ability as a rectangular array, which has a two-time bigger size than that of the former. Consequently, the MIMO array can not only save a great number of sensors, but halve the array size, when compared to a rectangular array with the same cross-range resolution. Computer simulations are provided to demonstrate the effectiveness of the proposed imaging approach.展开更多
Based on the general geometric model of multi-baseline Synthetic Aperture Radar Tomography （TomoSAR）, the three-dimensional （3-D） sampling criteria, the analytic expression of the 3-D Point Spread Function （PSF）...Based on the general geometric model of multi-baseline Synthetic Aperture Radar Tomography （TomoSAR）, the three-dimensional （3-D） sampling criteria, the analytic expression of the 3-D Point Spread Function （PSF） and the 3-D resolution are derived in the 3-D wavenumber domain in this paper. Considering the relationship between the observation geometry and the size of illuminated scenario, a 3-D Range Migration Algorithm with Elevation Digital Spotlighting （RMA-EDS） is proposed. With this algorithm 3-D images of the area of interest can be directly and accurately reconstructed in the 3-D space avoiding the complex operations of 3-D geometric correction. Finally, theoretical analyses and simulation results are presented to demonstrate the shift-varying property of the 3-D PSF and the spatialvarying property of the 3-D resolution and to demonstrate the validity of the 3-D RMA-EDS.展开更多
基金This work was supported by the General Design Department,China Academy of Space Technology(10377).
文摘The spaceborne synthetic aperture radar(SAR)sparse flight 3-D imaging technology through multiple observations of the cross-track direction is designed to form the cross-track equivalent aperture,and achieve the third dimensionality recognition.In this paper,combined with the actual triple star orbits,a sparse flight spaceborne SAR 3-D imaging method based on the sparse spectrum of interferometry and the principal component analysis(PCA)is presented.Firstly,interferometric processing is utilized to reach an effective sparse representation of radar images in the frequency domain.Secondly,as a method with simple principle and fast calculation,the PCA is introduced to extract the main features of the image spectrum according to its principal characteristics.Finally,the 3-D image can be obtained by inverse transformation of the reconstructed spectrum by the PCA.The simulation results of 4.84 km equivalent cross-track aperture and corresponding 1.78 m cross-track resolution verify the effective suppression of this method on high-frequency sidelobe noise introduced by sparse flight with a sparsity of 49%and random noise introduced by the receiver.Meanwhile,due to the influence of orbit distribution of the actual triple star orbits,the simulation results of the sparse flight with the 7-bit Barker code orbits are given as a comparison and reference to illuminate the significance of orbit distribution for this reconstruction results.This method has prospects for sparse flight 3-D imaging in high latitude areas for its short revisit period.
基金Supported by the National Natural Science Foundation of China General Programs(Nos.61072112,61372186)the National Natural Science Foundation of China Key Program(No.60890071)
文摘Downward Looking Sparse Linear Array Three Dimensional SAR(DLSLA 3D SAR) is an important form of 3D SAR imaging, which has a widespread application field. Since its practical equivalent phase centers are usually distributed sparsely and nonuniformly, traditional 3D SAR algorithms suffer from low resolution and high sidelobes in cross-track dimension. To deal with this problem, this paper introduces a method based on back-projection and convex optimization to achieve 3D high accuracy imaging reconstruction. Compared with traditional SAR algorithms, the proposed method sufficiently utilizes the sparsity of the 3D SAR imaging scene and can achieve lower sidelobes and higher resolution in cross-track dimension. In the simulated experiments, the reconstructed results of both simple and complex imaging scene verify that the proposed method outperforms 3D back-projection algorithm and shows satisfying cross-track dimensional resolution and good robustness to noise.
基金Supported by the National Basic Research Program (973) of China (No. 2009CB72400)
文摘The airborne cross-track three apertures MilliMeter Wave (MMW) Synthetic Aperture Radar (SAR) side-looking three-Dimensional (3D) imaging is investigated in this paper. Three apertures are distributed along the cross-track direction, and three virtual phase centers will be obtained through one-input and three-output. These three virtual phase centers form a sparse array which can be used to obtain the cross-track resolution. Because the cross-track array is short, the cross-track resolution is low. When the system works in side-looking mode, the cross-track resolution and height resolution will be coupling, and the low cross-track resolution will partly be transformed into the height uncertainty. The beam pattern of the real aperture is used as a weight to improve the Peak to SideLobe Ratio (PSLR) and Integrated SideLobe Ratio (ISLR) of the cross-track sparse array. In order to suppress the high cross-track sidelobes, a weighting preprocessing method is proposed. The 3D images of a point target and a simulation scene are achieved to verify the feasibility of the proposed method. And the imaging result of the real data obtained by the cross-track three-baseline MMW InSAR prototype is presented as a beneficial attempt.
基金Supported by the National Key Basic Research and Development Program(973 Program)(2014CB046405)
文摘In this paper a new spherical actuator is designed and its advantages are compared to an existing spherical actuator, which function is limited by several design bottlenecks. First the output torque is too small. Second, the attitude is difficult to be accurately detected. The new three-dimen- sional magnetic pole array can solve these major problems. The new actuator features an outer rotor with multiple permanent magnet （PM） poles. Using an analytical solution and the finite element so- lution simulation, the feasibility of the approach is verified. A prototype was developed, tested, and experiments were conducted to obtain the practical value of the magnetic flux density.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2010CB327702)
文摘As a 3-D display technology,stereoscopic imaging with lenticular lens sheet can only offer viewers the horizontal parallax.To reconstruct the 3-D image with parallax in both horizontal and vertical directions,the full parallax technique with micro-lens array was proposed.But due to the fabrication constraints and cost concerns of the micro-lens array,application of the full parallax technique is restricted in practice.In this paper we revisited the lenticular sheet method and cross-lenticular lens array formed by two lenticular sheets overlapped orthogonally.By analyzing the optical properties of this cross-lenticular lens array,we found that it has reasonable imaging qualities as a conventional micro-lens array.Besides,due to the poor optical property of the outskirt area of the cross-lenticular lens,the cross-lenticular lens array has better crosstalk suppression capability than the conventional one.Based on the analysis,in this paper,we used the proposed lens array to reconstruct a 3-D image and verified its practicability.The cross-lenticular lens array was found feasible to take the full parallax technique into commercial applications,with comparable advantages in terms of low-cost and easy fabrication over a large area.
基金supported by the National Key Basic Research and Development Program of China(Grant No.2018YFC1503603)the National Natural Science Foundation of China(Grant No.42030112)+3 种基金the Nature Science Foundation of Hunan Province(Grant No.2020JJ2043)the Project of Innovation-driven Plan of Central South University(Grant No.2019CX007)the Fundamental Research Funds for the Central Universities of Central South University(Grant Nos.2018zzts684 and 2019zzts011)the Hunan Provincial Innovation Foundation For Postgraduate(Grant No.CX20190067)。
文摘On 22 nd May 2021(local time),an earthquake of M_(s)7.4 struck Maduo county in Qinghai Province,China.This was the largest earthquake in China since the 2008 Wenchuan earthquake.In this study,ascending/descending Sentinel-1 and advanced land observation satellite-2(ALOS-2)synthetic aperture radar(SAR)images were used to derive the three-dimensional(3-D)coseismic displacements of this earthquake.We used the differential interferometric SAR(In SAR,DIn SAR),pixel offset-tracking(POT),multiple aperture In SAR(MAI),and burst overlap interferometry(BOI)methods to derive the displacement observations along the line-of-sight(LOS)and azimuth directions.To accurately mitigate the effect of ionospheric delay on the ALOS-2 DIn SAR observations,a polynomial fitting method was proposed to optimize range-spectrum-split-derived ionospheric phases.In addition,the 3-D displacement field was obtained by a strain model and variance component estimation(SM-VCE)method based on the high-quality SAR displacement observations.Results indicated that a left-lateral fault slip with the largest horizontal displacement of up to 2.4 m dominated this earthquake,and the small-magnitude vertical displacement with an alternating uplift/subsidence pattern along the fault trace was more concentrated in the near-fault regions.Comparison with the global navigation satellite system data indicated that the SM-VCE method can significantly improve the accuracy of the displacements compared to the classical weighted least squares method,and the incorporation of the BOI displacements can substantially benefit the accuracy of north-south displacement.In addition to the displacements,three coseismic strain invariants calculated based on the strain model parameters were also investigated.It was found that the eastern and western parts of the faults suffered more significant strains compared with the epicenter region.
基金supported in part by the Doctorate Foundation of Northwestern Polytechnical University(Grant No. CX201101)
文摘To obtain high cross-range resolution, the underwater 3-D acoustic imaging system usually requires a rectangular array with a great number of sensors and a large physical size. To reduce the sensor number and the array physical size simultaneously, this paper proposes a new underwater 3-D acoustic imaging approach based on a novel multiple-input multiple-output (MIMO) array. Specifically, the MIMO array is composed of four uniform linear arrays (ULAs) located on four sides of a rectangle. The transmitting array composed of two ULAs is located on a pair of opposite sides, and the receiving array composed of another two ULAs is located on the other two sides. Furthermore, narrowband waveforms coded with orthogonal polyphase sequences are employed as transmitting waveforms. When the subcode numbers in the polyphase coded sequences are sufficient, the MIMO array has the same 3-D imaging ability as a rectangular array, which has a two-time bigger size than that of the former. Consequently, the MIMO array can not only save a great number of sensors, but halve the array size, when compared to a rectangular array with the same cross-range resolution. Computer simulations are provided to demonstrate the effectiveness of the proposed imaging approach.
基金Supported by the National Science Fund for Distinguished Young Scholars (Grant No. 60725103)the National Natural Science Foundation ofChina (Grant No. 60602015)+1 种基金the National Key Laboratory Foundation (Grant No. 9140C1903030603)the Knowledge Innovation Programof Chinese Academy of Sciences (Grant No. 07QNCX-1154)
文摘Based on the general geometric model of multi-baseline Synthetic Aperture Radar Tomography （TomoSAR）, the three-dimensional （3-D） sampling criteria, the analytic expression of the 3-D Point Spread Function （PSF） and the 3-D resolution are derived in the 3-D wavenumber domain in this paper. Considering the relationship between the observation geometry and the size of illuminated scenario, a 3-D Range Migration Algorithm with Elevation Digital Spotlighting （RMA-EDS） is proposed. With this algorithm 3-D images of the area of interest can be directly and accurately reconstructed in the 3-D space avoiding the complex operations of 3-D geometric correction. Finally, theoretical analyses and simulation results are presented to demonstrate the shift-varying property of the 3-D PSF and the spatialvarying property of the 3-D resolution and to demonstrate the validity of the 3-D RMA-EDS.
