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Editor Work2013 Vol. 2, No. 3
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2013, 2(3): 265-270.
Abstract
1557KB
The echo data can be modeled as the product of the Toeplitz matrix and reflectivity of the observed scene. The row of the Toeplitz matrix is the time-shift of the transmitted signal. Since, it is difficult to vertify whether the Toeplitz matrix satisfis the reconstruct condition of sparse microwave imaging (such as, restricted isometry property), analyzing the performance of the transmitted signal in sparse microwave imaging is a problem. RIPless, a new progress in sparse signal processing, shows if the row of the matrix is an i.i.d. random vector drawn from a distribution, and this distribution satisfies certain conditions, then one can faithfully recover approximately sparse signals from a minimal number of measurements. Toeplitz matrix satisfies RIPless. In this paper, we first introduce the construction of measurement matrix in sparse microwave imaging. Then the relationship of pulse duration, bandwidth and waveform type and the number of measurements in sparse microwave imaging is analyzed. At last simulation results show that the effectiveness of proposed method.
The echo data can be modeled as the product of the Toeplitz matrix and reflectivity of the observed scene. The row of the Toeplitz matrix is the time-shift of the transmitted signal. Since, it is difficult to vertify whether the Toeplitz matrix satisfis the reconstruct condition of sparse microwave imaging (such as, restricted isometry property), analyzing the performance of the transmitted signal in sparse microwave imaging is a problem. RIPless, a new progress in sparse signal processing, shows if the row of the matrix is an i.i.d. random vector drawn from a distribution, and this distribution satisfies certain conditions, then one can faithfully recover approximately sparse signals from a minimal number of measurements. Toeplitz matrix satisfies RIPless. In this paper, we first introduce the construction of measurement matrix in sparse microwave imaging. Then the relationship of pulse duration, bandwidth and waveform type and the number of measurements in sparse microwave imaging is analyzed. At last simulation results show that the effectiveness of proposed method.
2013, 2(3): 271-277.
Sparse microwave imaging requires nonlinear algorithm that is expensive for large scene imaging. Therefore, the sub-block imaging method is studied, in which the measured data and the relative imaging region is divided into sub-blocks, and then sparse microwave imaging algorithm based on Least absolute shrinkage and selection operator (Lasso) is performed on each sub-block, finally the sub-blocks are combined to obtain the whole image of the large scene. Compared to the overall reconstruction of the sparse scene, sub-block algorithm can control data amount involved in each reconstruction, so as to avoid the signal processor frequently accessing the disk, which will cost huge time. Indeed, the theoretical analysis illustrates that the sub-block sparse imaging method is also accurate and stable, and the associated reconstruction error is no more than two times of that of the overall reconstruction. The result proved by simulation and real data processing supports the validity of our method.
Sparse microwave imaging requires nonlinear algorithm that is expensive for large scene imaging. Therefore, the sub-block imaging method is studied, in which the measured data and the relative imaging region is divided into sub-blocks, and then sparse microwave imaging algorithm based on Least absolute shrinkage and selection operator (Lasso) is performed on each sub-block, finally the sub-blocks are combined to obtain the whole image of the large scene. Compared to the overall reconstruction of the sparse scene, sub-block algorithm can control data amount involved in each reconstruction, so as to avoid the signal processor frequently accessing the disk, which will cost huge time. Indeed, the theoretical analysis illustrates that the sub-block sparse imaging method is also accurate and stable, and the associated reconstruction error is no more than two times of that of the overall reconstruction. The result proved by simulation and real data processing supports the validity of our method.
2013, 2(3): 278-283.
Beamforming of Ultra Wide Band (UWB) signals is a crucial technology in UWB radar. Conventional beamforming methods have limitations in instantaneous bandwidth, scanning range, beam pattern deviation and a mainlobe distortion. Direct Time Delay (DTD) compensation is an effective way to avoid above problems. In this paper, a DTD compensation based on Hermite interpolation filters is presented to implement beamforming of UWB signals. Theoretical analysis and simulation results show that the magnitude responses and group delay of the proposed filters are better than those based on Lagrange and Radial basis methods. The demonstration of the UWB Linear-Frequency modulated (LFM) signal also shows excellent performances on the UWB beamforming of the proposed method.
Beamforming of Ultra Wide Band (UWB) signals is a crucial technology in UWB radar. Conventional beamforming methods have limitations in instantaneous bandwidth, scanning range, beam pattern deviation and a mainlobe distortion. Direct Time Delay (DTD) compensation is an effective way to avoid above problems. In this paper, a DTD compensation based on Hermite interpolation filters is presented to implement beamforming of UWB signals. Theoretical analysis and simulation results show that the magnitude responses and group delay of the proposed filters are better than those based on Lagrange and Radial basis methods. The demonstration of the UWB Linear-Frequency modulated (LFM) signal also shows excellent performances on the UWB beamforming of the proposed method.
2013, 2(3): 284-291.
The output SINR (Signal to Interference and Noise Ratio) of oblique projection and orthogonal projection filtering based on polarization sensitive array is investigated. The output SINR formulas of oblique projection and orthogonal projection filtering under both the ideal and array error conditions are derived. Related with the spatial and polarized matching coefficient between signal and interference under ideal condition, the output SINR is the function of the spatial and polarized matching coefficient between signal and interference, the Interference to Noise Ratio (INR), and the perturbation momentum under array error condition. The oblique projection filtering obtains the same output SINR as the orthogonal projection filtering under both conditions, while the output SINR of the maximum SINR principle filtering is the best. Further analysis shows that the oblique projection distorts the spatial and polarized properties of noise filtering while keeps the amplitude and phase properties of output signal which are distorted employing the orthogonal filtering. The simulation results attest the reasonability of the analysis of the paper.
The output SINR (Signal to Interference and Noise Ratio) of oblique projection and orthogonal projection filtering based on polarization sensitive array is investigated. The output SINR formulas of oblique projection and orthogonal projection filtering under both the ideal and array error conditions are derived. Related with the spatial and polarized matching coefficient between signal and interference under ideal condition, the output SINR is the function of the spatial and polarized matching coefficient between signal and interference, the Interference to Noise Ratio (INR), and the perturbation momentum under array error condition. The oblique projection filtering obtains the same output SINR as the orthogonal projection filtering under both conditions, while the output SINR of the maximum SINR principle filtering is the best. Further analysis shows that the oblique projection distorts the spatial and polarized properties of noise filtering while keeps the amplitude and phase properties of output signal which are distorted employing the orthogonal filtering. The simulation results attest the reasonability of the analysis of the paper.
2013, 2(3): 292-299.
As a batch processing method, the Hough transform hardly overcomes the accumulation phenomenon of single-scan data sets for it gets confused with the time sequence information of measurements. To solve this nonlinear problem, a track initiation method based on the parallel Hough transform that changes the processing structure of the Hough transform and the accumulating manner of the counter is proposed. After mapping sets of different time measurements to the parameter space separately, the accumulated result of the measurement sets with the same index constitute an accumulated vector. According to the rules, the value of the accumulator can be obtained using the sliding window method. Finally, we make a decision on whether to initiate a track or not through threshold detection. Simulation experiment results of track initiation problems with different scan times under heavy clutters show the efficiency of the parallel Hough transform.
As a batch processing method, the Hough transform hardly overcomes the accumulation phenomenon of single-scan data sets for it gets confused with the time sequence information of measurements. To solve this nonlinear problem, a track initiation method based on the parallel Hough transform that changes the processing structure of the Hough transform and the accumulating manner of the counter is proposed. After mapping sets of different time measurements to the parameter space separately, the accumulated result of the measurement sets with the same index constitute an accumulated vector. According to the rules, the value of the accumulator can be obtained using the sliding window method. Finally, we make a decision on whether to initiate a track or not through threshold detection. Simulation experiment results of track initiation problems with different scan times under heavy clutters show the efficiency of the parallel Hough transform.
2013, 2(3): 300-308.
Currently, high-resolution imaging of a high-speed warhead is a popular topic in the field of radar technology. In contrast with regular targets, a high-speed warhead often moves along its trajectory and simultaneously exhibits a special spinning movement. The echoes from a radar sensor can contain complex Doppler information presenting a severe challenge to the high-resolution imaging procedure. This paper investigates imaging methods for a high-speed warhead considering the spinning movement. First, the radar echo characteristics of the spinning warhead are studied and the echo phase characteristics are revealed. Next, the chirp-rate estimation method using the WignerHough Transform (WHT) for the trajectory movement compensation and the imaging method based on spinning are proposed. Finally, the validity and the advantage of the spin-based imaging method are tested with simulation data. Test results indicate that the imaging algorithm is robust when the data reaches a certain SNR, and this paper provides a better solution to the issue of speed estimation and the complexity of imaging algorithm of a high-speed warhead.
Currently, high-resolution imaging of a high-speed warhead is a popular topic in the field of radar technology. In contrast with regular targets, a high-speed warhead often moves along its trajectory and simultaneously exhibits a special spinning movement. The echoes from a radar sensor can contain complex Doppler information presenting a severe challenge to the high-resolution imaging procedure. This paper investigates imaging methods for a high-speed warhead considering the spinning movement. First, the radar echo characteristics of the spinning warhead are studied and the echo phase characteristics are revealed. Next, the chirp-rate estimation method using the WignerHough Transform (WHT) for the trajectory movement compensation and the imaging method based on spinning are proposed. Finally, the validity and the advantage of the spin-based imaging method are tested with simulation data. Test results indicate that the imaging algorithm is robust when the data reaches a certain SNR, and this paper provides a better solution to the issue of speed estimation and the complexity of imaging algorithm of a high-speed warhead.
2013, 2(3): 309-313.
To improve the computational efficiency of system feature extraction, reduce the occupied memory space, and simplify the program design, a modified gradient descent method on Stiefel manifold is proposed based on the optimization algorithm of geometry frame on the Riemann manifold. Different geodesic calculation formulas are used for different scenarios. A polynomial is also used to lie close to the geodesic equations. JiuZhaoQin-Horner polynomial algorithm and the strategies of line-searching technique and change of the step size of iteration are also adopted. The gradient descent algorithm on Stiefel manifold applied in Principal Component Analysis (PCA) is discussed in detail as an example of system feature extraction. Theoretical analysis and simulation experiments show that the new method can achieve superior performance in both the convergence rate and calculation efficiency while ensuring the unitary column orthogonality. In addition, it is easier to implement by software or hardware.
To improve the computational efficiency of system feature extraction, reduce the occupied memory space, and simplify the program design, a modified gradient descent method on Stiefel manifold is proposed based on the optimization algorithm of geometry frame on the Riemann manifold. Different geodesic calculation formulas are used for different scenarios. A polynomial is also used to lie close to the geodesic equations. JiuZhaoQin-Horner polynomial algorithm and the strategies of line-searching technique and change of the step size of iteration are also adopted. The gradient descent algorithm on Stiefel manifold applied in Principal Component Analysis (PCA) is discussed in detail as an example of system feature extraction. Theoretical analysis and simulation experiments show that the new method can achieve superior performance in both the convergence rate and calculation efficiency while ensuring the unitary column orthogonality. In addition, it is easier to implement by software or hardware.
2013, 2(3): 314-318.
Broad band Digital Beam Forming (DBF) is the key technique for the realization of Digital Array Radar (DAR). We propose the method of combination realization of the channel equalization and DBF time delay filter function by using adaptive Sample Matrix Inversion algorithm. The broad band DBF function is realized on a new DBF module based on parallel fiber optic engines and Field Program Gate Array (FPGA). Good performance is achieved when it is used to some radar products.
Broad band Digital Beam Forming (DBF) is the key technique for the realization of Digital Array Radar (DAR). We propose the method of combination realization of the channel equalization and DBF time delay filter function by using adaptive Sample Matrix Inversion algorithm. The broad band DBF function is realized on a new DBF module based on parallel fiber optic engines and Field Program Gate Array (FPGA). Good performance is achieved when it is used to some radar products.
2013, 2(3): 319-325.
This paper analyses the geometry of sliding spotlight FMCW-SAR, sets up the echo model and derives the two-dimensional spectrum of its echo signal. According to its signal characteristics a subaperture wavenumberdomain algorithm is presented, which corrects the Doppler Frequency Shift Effect caused by the motion within the sweep. The algorithm can acquire the images with azimuth resolution better than that obtained in the stripmap case by the subaperture coherent recombination and with an imaged area larger than that achieved in the spotlight operation by adjoining the subaperture images. Rationality of the echo model and the effectiveness of the proposed algorithm are verified by the simulation results and analysis.
This paper analyses the geometry of sliding spotlight FMCW-SAR, sets up the echo model and derives the two-dimensional spectrum of its echo signal. According to its signal characteristics a subaperture wavenumberdomain algorithm is presented, which corrects the Doppler Frequency Shift Effect caused by the motion within the sweep. The algorithm can acquire the images with azimuth resolution better than that obtained in the stripmap case by the subaperture coherent recombination and with an imaged area larger than that achieved in the spotlight operation by adjoining the subaperture images. Rationality of the echo model and the effectiveness of the proposed algorithm are verified by the simulation results and analysis.
2013, 2(3): 326-333.
Airborne differential synthetic aperture radar interferometry (D-InSAR) is a kind of potential technology to survey the surface deformation. In this paper, the errors of two usually used modes of this technology, namely, two-pass and three-pass approaches, are compared and analyzed. In the analysis, all the errors are decomposed and sorted according to the principle of independence, and the coupling between motion error and other errors is considered. Based on the analysis, analytical expressions are derived for the deformation measurement errors in the two modes. The results demonstrate that when the amplitude of the motion error is small, the three-pass approach can reduce the requirement on the precision of the external topography data, so it distinctly outperforms the two-pass approach; when the amplitude of the motion error is large, high-precision topography data are needed in the three-pass approach, and as a result, its advantage over the two-pass approach is not distinct any more.
Airborne differential synthetic aperture radar interferometry (D-InSAR) is a kind of potential technology to survey the surface deformation. In this paper, the errors of two usually used modes of this technology, namely, two-pass and three-pass approaches, are compared and analyzed. In the analysis, all the errors are decomposed and sorted according to the principle of independence, and the coupling between motion error and other errors is considered. Based on the analysis, analytical expressions are derived for the deformation measurement errors in the two modes. The results demonstrate that when the amplitude of the motion error is small, the three-pass approach can reduce the requirement on the precision of the external topography data, so it distinctly outperforms the two-pass approach; when the amplitude of the motion error is large, high-precision topography data are needed in the three-pass approach, and as a result, its advantage over the two-pass approach is not distinct any more.
2013, 2(3): 334-347.
When applying to the airborne repeat-pass Interferometric Synthetic Aperture Radar (InSAR), which has long synthetic aperture and large azimuth-dependent errors, the surface assumption used to simply the time-domain algorithm model and the residual motion errors due to the precision of the navigation system will affect the imaging result and the interferometric measurement. This paper analyzes the altitude errors introduced by the surface assumption and the residual motion errors due to the precision of the navigation system. We deduce the range errors model during the single pass and analyze the effects of these errors on the plane location, interferometric phase and DEM precision. Then the accuracy of the theoretical deduction is verified by simulation and real data. The research provides theoretical bases for the system design and signal processing of airborne repeat-pass InSAR.
When applying to the airborne repeat-pass Interferometric Synthetic Aperture Radar (InSAR), which has long synthetic aperture and large azimuth-dependent errors, the surface assumption used to simply the time-domain algorithm model and the residual motion errors due to the precision of the navigation system will affect the imaging result and the interferometric measurement. This paper analyzes the altitude errors introduced by the surface assumption and the residual motion errors due to the precision of the navigation system. We deduce the range errors model during the single pass and analyze the effects of these errors on the plane location, interferometric phase and DEM precision. Then the accuracy of the theoretical deduction is verified by simulation and real data. The research provides theoretical bases for the system design and signal processing of airborne repeat-pass InSAR.
2013, 2(3): 348-356.
Under the geometry of geosynchronous satellite-air bistatic SAR where the geosynchronous satellite is the transmitter and aerostat is the receiver, in order to suppress clutter and detect slowly moving target using Space Time Adaptive Processing (STAP), it is necessary to analyze the clutter characteristics. From the point of view of ground moving target indication, the theory model of the clutter characteristics under the geometry of geosynchronous satellite-space bistatic SAR is analyzed and established in this paper; especially, the range-dependence characteristics of the angle-Doppler curve of the clutter is analyzed. Finally, the simulation verifies correctness of the analysis. The theory model and the conclusion in this paper indicates the clutter characteristics of the new geosynchronous satellite-air bistatic SAR mode, and provide theory basis for the selection and research of ground moving target indication method under this mode.
Under the geometry of geosynchronous satellite-air bistatic SAR where the geosynchronous satellite is the transmitter and aerostat is the receiver, in order to suppress clutter and detect slowly moving target using Space Time Adaptive Processing (STAP), it is necessary to analyze the clutter characteristics. From the point of view of ground moving target indication, the theory model of the clutter characteristics under the geometry of geosynchronous satellite-space bistatic SAR is analyzed and established in this paper; especially, the range-dependence characteristics of the angle-Doppler curve of the clutter is analyzed. Finally, the simulation verifies correctness of the analysis. The theory model and the conclusion in this paper indicates the clutter characteristics of the new geosynchronous satellite-air bistatic SAR mode, and provide theory basis for the selection and research of ground moving target indication method under this mode.
2013, 2(3): 357-366.
A Fast Back Projection (FBP) algorithm for spotlight mode Bistatic Synthetic Aperture Radar (Bi-SAR) was presented. Sync channel signal from land receiver was taken as matched filter for echo signal in the phase of range compression, and the secondary phase calibration decreased the approximation error effects for FBP algorithm in the phase of azimuth compression. Computational complexity of this algorithm was O(N2.5 ). In addition, this algorithm was validated on Graphic Processing Unit (GPU) by simulation data and measured data.
A Fast Back Projection (FBP) algorithm for spotlight mode Bistatic Synthetic Aperture Radar (Bi-SAR) was presented. Sync channel signal from land receiver was taken as matched filter for echo signal in the phase of range compression, and the secondary phase calibration decreased the approximation error effects for FBP algorithm in the phase of azimuth compression. Computational complexity of this algorithm was O(N2.5 ). In addition, this algorithm was validated on Graphic Processing Unit (GPU) by simulation data and measured data.
2013, 2(3): 367-381.
Due to its agility, flexibility and accuracy, airborne repeat-pass Interferometric Synthetic Aperture Radar (InSAR) is capable of overcoming the disadvantages of long revisit time and low resolution in space-borne SAR interferometry, and play an irreplaceable role in monitoring the deformation of landslides, volcanoes, earthquakes, etc. In this paper, the history and status in the world wide about the technology of airborne repeat-pass SAR interferometry are reviewed detailedly. Then after the accuracy of this technology is analyzed, its key problems in practice are presented, and the related researches in this field are also introduced comprehensively. The development trend and the prospect of this technology are also described in this paper. Finally, it is pointed that several problems still need to be studied further for accurate parameter inversion.
Due to its agility, flexibility and accuracy, airborne repeat-pass Interferometric Synthetic Aperture Radar (InSAR) is capable of overcoming the disadvantages of long revisit time and low resolution in space-borne SAR interferometry, and play an irreplaceable role in monitoring the deformation of landslides, volcanoes, earthquakes, etc. In this paper, the history and status in the world wide about the technology of airborne repeat-pass SAR interferometry are reviewed detailedly. Then after the accuracy of this technology is analyzed, its key problems in practice are presented, and the related researches in this field are also introduced comprehensively. The development trend and the prospect of this technology are also described in this paper. Finally, it is pointed that several problems still need to be studied further for accurate parameter inversion.
2013, 2(3): 382-388.
In this paper, the false target discrimination strategy of air surveillance radar is studied. Aiming to distinguish false target which can form certain track such as clutter residual false track or false track deception, a novel method based on track velocity modification and frequency spectrum analysis is proposed here, which can provide a great potential approach for solving the false target discrimination puzzle. The discrimination issue is concluded as a problem of bivariate test of hypothesis, and the likelihood ratio formula is deduced with the way to calculate the judge threshold also proposed. The validity of the novel method is verified by experimental results of real surveillance radar data.
In this paper, the false target discrimination strategy of air surveillance radar is studied. Aiming to distinguish false target which can form certain track such as clutter residual false track or false track deception, a novel method based on track velocity modification and frequency spectrum analysis is proposed here, which can provide a great potential approach for solving the false target discrimination puzzle. The discrimination issue is concluded as a problem of bivariate test of hypothesis, and the likelihood ratio formula is deduced with the way to calculate the judge threshold also proposed. The validity of the novel method is verified by experimental results of real surveillance radar data.
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