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Editor Work2014 Vol. 3, No. 1
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2014, 3(1): 1-9.
Abstract
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This study concentrates on the results of several advanced hybrid bistatic SAR experiments. The hybrid bistatic configuration applies to the case in which the transmitter and receiver are mounted on different types of platforms, e.g., spaceborne/airborne, airborne/stationary, spaceborne/stationary, and so on. Several hybrid bistatic SAR experiments have been performed successfully, i.e., TerraSAR-X/PAMIR, PAMIR/stationary, and TerraSAR-X/stationary. Furthermore, Multiple Baseline Interferometry SAR (MB-InSAR) and Digital Beam-Forming (DBF) technologies are validated in the TerraSAR-X/stationary configuration. Note that the DBF experiment results based on the spaceborne illuminator are discussed for the first time in SAR community. In addition, this paper emphasizes imaging geometry, image analysis, and focusing results.
This study concentrates on the results of several advanced hybrid bistatic SAR experiments. The hybrid bistatic configuration applies to the case in which the transmitter and receiver are mounted on different types of platforms, e.g., spaceborne/airborne, airborne/stationary, spaceborne/stationary, and so on. Several hybrid bistatic SAR experiments have been performed successfully, i.e., TerraSAR-X/PAMIR, PAMIR/stationary, and TerraSAR-X/stationary. Furthermore, Multiple Baseline Interferometry SAR (MB-InSAR) and Digital Beam-Forming (DBF) technologies are validated in the TerraSAR-X/stationary configuration. Note that the DBF experiment results based on the spaceborne illuminator are discussed for the first time in SAR community. In addition, this paper emphasizes imaging geometry, image analysis, and focusing results.
2014, 3(1): 10-18.
Recently, a novel conception of Synthetic Aperture Radar (SAR) based on Multi-Input Multi-Output (MIMO) technology draws much attention for its potential advantages. MIMO-SAR could obtain much more equivalent channels than the number of the physical array elements by simultaneously utilizing multiple antennas at transmission and reception. These additional channels are demonstrated to be useful for the application of High-Resolution Wide-Swath (HRWS) imaging and slowly moving target indication. In this paper, a detailed discussion on the conception and connotation of MIMO-SAR is made firstly, and then the investigation states of MIMO-SAR, such as high range resolution SAR imaging, three-dimensional down-looking SAR imaging, HRWS imaging and Ground Moving Target Indication (GMTI), are discussed. Base on the discussion mentioned above, the advantages and disadvantages of MIMO-SAR system are analyzed, and the key technical issues in MIMO-SAR are summarized. At last, the prospects of MIMO-SAR application are pointed out.
Recently, a novel conception of Synthetic Aperture Radar (SAR) based on Multi-Input Multi-Output (MIMO) technology draws much attention for its potential advantages. MIMO-SAR could obtain much more equivalent channels than the number of the physical array elements by simultaneously utilizing multiple antennas at transmission and reception. These additional channels are demonstrated to be useful for the application of High-Resolution Wide-Swath (HRWS) imaging and slowly moving target indication. In this paper, a detailed discussion on the conception and connotation of MIMO-SAR is made firstly, and then the investigation states of MIMO-SAR, such as high range resolution SAR imaging, three-dimensional down-looking SAR imaging, HRWS imaging and Ground Moving Target Indication (GMTI), are discussed. Base on the discussion mentioned above, the advantages and disadvantages of MIMO-SAR system are analyzed, and the key technical issues in MIMO-SAR are summarized. At last, the prospects of MIMO-SAR application are pointed out.
2014, 3(1): 19-27.
Compared with other bands, the millimeter wave Interferometric Synthetic Aperture Radar (InSAR) has high accuracy and small size, which is a hot topic in InSAR research. On the other hand, shorter wavelength causes difficulties in 2D imaging and interferometric phase extraction. In this study, the imaging and phase performance of the streaming Back Projection (BP) method combined with IMU data are analyzed and discussed on the basis of actual Ka-band InSAR data. It is found that because the wavelength of the Ka-band is short, it is more sensitive to the antenna phase-center history. To ensure the phase-preserving capacity, the IMU data must be used with accurate motion error compensation. Furthermore, during data processing, we verify the flat-earth-removing capacity of the BP algorithm that calculates and compensates the master and slave antenna phase centers individually.
Compared with other bands, the millimeter wave Interferometric Synthetic Aperture Radar (InSAR) has high accuracy and small size, which is a hot topic in InSAR research. On the other hand, shorter wavelength causes difficulties in 2D imaging and interferometric phase extraction. In this study, the imaging and phase performance of the streaming Back Projection (BP) method combined with IMU data are analyzed and discussed on the basis of actual Ka-band InSAR data. It is found that because the wavelength of the Ka-band is short, it is more sensitive to the antenna phase-center history. To ensure the phase-preserving capacity, the IMU data must be used with accurate motion error compensation. Furthermore, during data processing, we verify the flat-earth-removing capacity of the BP algorithm that calculates and compensates the master and slave antenna phase centers individually.
2014, 3(1): 28-34.
Employing Polarimetric Interferometry Synthetic Aperture Radar (PolInSAR) data to inverse forest parameters is a hot topic in the research field of PolInSAR. The typical forest parameter inversion algorithm is the three-stage inversion algorithm based on Random Volume over Ground (RVoG) model. The errors of linear fitting and volume scattering correlation estimation are the major factors for parameter estimation accuracy. In this paper, straight line fitting employing the total least squares method is used to estimate the ground phase. Then, the Gamma function is applied as the line measure to adaptively estimate the volume scattering correlation. The improved three-stage inversion algorithm with PolInSAR is presented. The experiment result proves the forest parameters inversion result is accurate and reliable.
Employing Polarimetric Interferometry Synthetic Aperture Radar (PolInSAR) data to inverse forest parameters is a hot topic in the research field of PolInSAR. The typical forest parameter inversion algorithm is the three-stage inversion algorithm based on Random Volume over Ground (RVoG) model. The errors of linear fitting and volume scattering correlation estimation are the major factors for parameter estimation accuracy. In this paper, straight line fitting employing the total least squares method is used to estimate the ground phase. Then, the Gamma function is applied as the line measure to adaptively estimate the volume scattering correlation. The improved three-stage inversion algorithm with PolInSAR is presented. The experiment result proves the forest parameters inversion result is accurate and reliable.
2014, 3(1): 35-44.
The priority during speckle reduction in Polarimetric Synthetic Aperture Radar (Pol-SAR) data is to maintain the polarization information. For this reason, it is undesirable to separate each element of polarimetric SAR. Based on the multiplicative noise model and complex matrix, an effective distance similarity measure method is derived, which can process covariance matrix C or coherent matrix T directly. Experiments show that this method can effectively reduce speckle and maintain the polarization information, point targets, and texture structure. Moreover, it can handle large polarimetric SAR with simplicity and ease.
The priority during speckle reduction in Polarimetric Synthetic Aperture Radar (Pol-SAR) data is to maintain the polarization information. For this reason, it is undesirable to separate each element of polarimetric SAR. Based on the multiplicative noise model and complex matrix, an effective distance similarity measure method is derived, which can process covariance matrix C or coherent matrix T directly. Experiments show that this method can effectively reduce speckle and maintain the polarization information, point targets, and texture structure. Moreover, it can handle large polarimetric SAR with simplicity and ease.
For high resolution space-borne P-band SAR system, ionospheric effects could cause serious phase errors. These errors are causally related to the radar frequency and the TEC of ionosphere and make the image quality degraded. To guarantee the image quality, the ionosphere errors must be emended. Based on the mismatched filter model caused by ionosphere, it is pointed out that accurate ionosphere TEC is the key for phase error correction, a high precision ionosphere TEC measurement method is further put forward by using the phase errors of SAR echoes, which is validated by processing the data of a ground based P-band radar with well focused radar image of the international space station obtained. The results indicate that the method can effectively increase the accuracy of ionosphere TEC estimation, and thus improve the radar imaging quality, it is applicable to low frequency space-borne SAR systems for reducing the ionosphere effects.
For high resolution space-borne P-band SAR system, ionospheric effects could cause serious phase errors. These errors are causally related to the radar frequency and the TEC of ionosphere and make the image quality degraded. To guarantee the image quality, the ionosphere errors must be emended. Based on the mismatched filter model caused by ionosphere, it is pointed out that accurate ionosphere TEC is the key for phase error correction, a high precision ionosphere TEC measurement method is further put forward by using the phase errors of SAR echoes, which is validated by processing the data of a ground based P-band radar with well focused radar image of the international space station obtained. The results indicate that the method can effectively increase the accuracy of ionosphere TEC estimation, and thus improve the radar imaging quality, it is applicable to low frequency space-borne SAR systems for reducing the ionosphere effects.
2014, 3(1): 53-60.
In rough mountainous areas, beam-pointing mismatch problems always arise when a spaceborne Synthetic Aperture Radar (SAR) uses the traditional Digital BeamForming (DBF) approach in elevation to receive echoes, leading to the degradation of the receivers gain and system Signal-to-Noise Ratio (SNR). To solve this problem, an Adaptive Digital BeamForming (ADBF) approach based on the Capon spatial spectrum estimation is proposed. This approach first estimates the Angle Of Arrival (AOA) of the source signal in each range bin using the limited echo data. Then, it updates the weighting vector in the beamforming process, thereby enabling the receiving beams to precisely point to the signal source, and enhance the receivers gain and SNR.
Simulation results suggest that the ADBF approach significantly improves the performance compared to the SCan-On-REceive (SCORE) approach, exhibiting robustness to system and source parameters variations.
In rough mountainous areas, beam-pointing mismatch problems always arise when a spaceborne Synthetic Aperture Radar (SAR) uses the traditional Digital BeamForming (DBF) approach in elevation to receive echoes, leading to the degradation of the receivers gain and system Signal-to-Noise Ratio (SNR). To solve this problem, an Adaptive Digital BeamForming (ADBF) approach based on the Capon spatial spectrum estimation is proposed. This approach first estimates the Angle Of Arrival (AOA) of the source signal in each range bin using the limited echo data. Then, it updates the weighting vector in the beamforming process, thereby enabling the receiving beams to precisely point to the signal source, and enhance the receivers gain and SNR.
Simulation results suggest that the ADBF approach significantly improves the performance compared to the SCan-On-REceive (SCORE) approach, exhibiting robustness to system and source parameters variations.
2014, 3(1): 61-69.
Attitude Steering has been widely applied to the current low orbit SAR system to decrease the rang/azimuth coupling of the received data. This paper focuses on the impacts of attitude steering to the observation properties of Geo-SAR, namely, Doppler parameters, range swath, and rang cell migration effect, and a comparisonbetween 3 different ways of attitude steering is made. Based on the simulation results, the necessity of attitude steering for Geo-SAR is validated, and for Geo-SAR on elliptical orbit, 2D attitude steering is the most effective.
Attitude Steering has been widely applied to the current low orbit SAR system to decrease the rang/azimuth coupling of the received data. This paper focuses on the impacts of attitude steering to the observation properties of Geo-SAR, namely, Doppler parameters, range swath, and rang cell migration effect, and a comparisonbetween 3 different ways of attitude steering is made. Based on the simulation results, the necessity of attitude steering for Geo-SAR is validated, and for Geo-SAR on elliptical orbit, 2D attitude steering is the most effective.
2014, 3(1): 70-77.
To overcome the influence of non-ideal factor on the performance of moving target indication, such as the channel gain and phase response error and image registration error, an improving clutter rejection method is proposed. The algorithm combines the minimum variance clutter rejection method and the steering vector clutter rejection method. Firstly, the weight vector of minimum variance clutter rejection is calculated to construct registration image. Then clutter orthogonal subspace is calculated with registration image. Finally, clutter rejection is implemented with orthogonal subspace method. Theoretical analysis and experimental results show that the proposed method performs well and it can obtain higher SCNR than the minimum variance clutter rejection method and steering vector clutter rejection method when both image registration and channel amplitude and phase errors are big.
To overcome the influence of non-ideal factor on the performance of moving target indication, such as the channel gain and phase response error and image registration error, an improving clutter rejection method is proposed. The algorithm combines the minimum variance clutter rejection method and the steering vector clutter rejection method. Firstly, the weight vector of minimum variance clutter rejection is calculated to construct registration image. Then clutter orthogonal subspace is calculated with registration image. Finally, clutter rejection is implemented with orthogonal subspace method. Theoretical analysis and experimental results show that the proposed method performs well and it can obtain higher SCNR than the minimum variance clutter rejection method and steering vector clutter rejection method when both image registration and channel amplitude and phase errors are big.
2014, 3(1): 78-84.
The registration of SAR and optical remote sensing image is the basise for fusing of multi-source image and comprehensive analysis. In this paper a new fine registration method for SAR and optical image is proposed. Firstly, three to four corresponding points are selected manually to realize a coarse registration that eliminates the differences in scale and rotation. Many characteristic points in the optical image are detected and the corresponding points in SAR image are extracted using normalized gradient correlations based on the different gradients by operators. An irregular triangle network is constructed using these corresponding points and each triangle region is finely registered. Finally SAR image and optical image are finely registered. Experiment and processed results demonstrate the feasibility of this method.
The registration of SAR and optical remote sensing image is the basise for fusing of multi-source image and comprehensive analysis. In this paper a new fine registration method for SAR and optical image is proposed. Firstly, three to four corresponding points are selected manually to realize a coarse registration that eliminates the differences in scale and rotation. Many characteristic points in the optical image are detected and the corresponding points in SAR image are extracted using normalized gradient correlations based on the different gradients by operators. An irregular triangle network is constructed using these corresponding points and each triangle region is finely registered. Finally SAR image and optical image are finely registered. Experiment and processed results demonstrate the feasibility of this method.
2014, 3(1): 85-91.
Geometrical imaging models and calculations of orientation parameters are the main factors affecting the positioning of stereo Synthetic Aperture Radar (SAR) images. For accurate positioning with squint stereo SAR images and less Ground Control Points (GCPs), a positioning algorithm with one GCP is designed. In this algorithm, the position and velocity of the radar antenna phase center are derived using orbit parameters, and the close range and Doppler centroid of the SAR images are compensated by one GCP. Thus, accurate orientation parameters are obtained and accurate positioning with stereo SAR images is completed. Airborne SAR images acquired by the Chinese Academy of Surveying and Mapping are used in experiments. The positioning errors of the checkpoints are calculated and analyzed, and it verified the accuracy and effectiveness of the proposed method.
Geometrical imaging models and calculations of orientation parameters are the main factors affecting the positioning of stereo Synthetic Aperture Radar (SAR) images. For accurate positioning with squint stereo SAR images and less Ground Control Points (GCPs), a positioning algorithm with one GCP is designed. In this algorithm, the position and velocity of the radar antenna phase center are derived using orbit parameters, and the close range and Doppler centroid of the SAR images are compensated by one GCP. Thus, accurate orientation parameters are obtained and accurate positioning with stereo SAR images is completed. Airborne SAR images acquired by the Chinese Academy of Surveying and Mapping are used in experiments. The positioning errors of the checkpoints are calculated and analyzed, and it verified the accuracy and effectiveness of the proposed method.
2014, 3(1): 92-100.
This paper presents a novel feature extraction method for remote sensing imagery based on the cooperation of multiple ant colonies. First, multiresolution expression of the input remote sensing imagery is created, and two different ant colonies are spread on different resolution images. The ant colony in the low-resolution image uses phase congruency as the inspiration information, whereas that in the high-resolution image uses gradient magnitude. The two ant colonies cooperate to detect features in the image by sharing the same pheromone matrix. Finally, the image features are extracted on the basis of the pheromone matrix threshold. Because a substantial amount of information in the input image is used as inspiration information of the ant colonies, the proposed method shows higher intelligence and acquires more complete and meaningful image features than those of other simple edge detectors.
This paper presents a novel feature extraction method for remote sensing imagery based on the cooperation of multiple ant colonies. First, multiresolution expression of the input remote sensing imagery is created, and two different ant colonies are spread on different resolution images. The ant colony in the low-resolution image uses phase congruency as the inspiration information, whereas that in the high-resolution image uses gradient magnitude. The two ant colonies cooperate to detect features in the image by sharing the same pheromone matrix. Finally, the image features are extracted on the basis of the pheromone matrix threshold. Because a substantial amount of information in the input image is used as inspiration information of the ant colonies, the proposed method shows higher intelligence and acquires more complete and meaningful image features than those of other simple edge detectors.
2014, 3(1): 101-110.
This paper discusses the change detection in high-resolution SAR image interpretation. Referring to the unfavorable elements in the change detection and the status quo, this paper focuses on resolving the semantic information deficiency problem in SAR image change detection. A method named change detection base on Bag of Words Model (BoWM) is proposed. By using the BoWM, two visual histograms of two different temporal images are obtained, and the histogram difference, which contains semantic information, is defined as the change vector. By analyzing the change vector and combining it with the statistical change detection method, the semantic analysis and interest change-type detection of the change area can be obtained. Experiments show that the proposed method may be applicable to the semantic analysis of the change area in high-resolution SAR images.
This paper discusses the change detection in high-resolution SAR image interpretation. Referring to the unfavorable elements in the change detection and the status quo, this paper focuses on resolving the semantic information deficiency problem in SAR image change detection. A method named change detection base on Bag of Words Model (BoWM) is proposed. By using the BoWM, two visual histograms of two different temporal images are obtained, and the histogram difference, which contains semantic information, is defined as the change vector. By analyzing the change vector and combining it with the statistical change detection method, the semantic analysis and interest change-type detection of the change area can be obtained. Experiments show that the proposed method may be applicable to the semantic analysis of the change area in high-resolution SAR images.
2014, 3(1): 111-118.
In this study, the performance of three phase-modulated signals used in airborne Synthetic Aperture Ladar (SAL) is investigated. The transmitting and receiving modes and imaging processing methods for these signals are studied. Considering that the swath of the airborne SAL is very narrow, in order to reduce the AD sampling rate of the wideband signal, a phase-dechirping receiving mode is proposed for the phase-modulated signal based on the Linear Frequency Modulation (LFM) signal. The imaging simulation results for these three phase-modulated signals validate the effectiveness of the proposed method.
In this study, the performance of three phase-modulated signals used in airborne Synthetic Aperture Ladar (SAL) is investigated. The transmitting and receiving modes and imaging processing methods for these signals are studied. Considering that the swath of the airborne SAL is very narrow, in order to reduce the AD sampling rate of the wideband signal, a phase-dechirping receiving mode is proposed for the phase-modulated signal based on the Linear Frequency Modulation (LFM) signal. The imaging simulation results for these three phase-modulated signals validate the effectiveness of the proposed method.
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