Flat thin ice (<30 cm thick) is a common ice type in the Bohai Sea, China. Ice thickness detection is important to offshore exploration and marine transport in winter. Synthetic aperture radar (SAR) can be used to ...Flat thin ice (<30 cm thick) is a common ice type in the Bohai Sea, China. Ice thickness detection is important to offshore exploration and marine transport in winter. Synthetic aperture radar (SAR) can be used to acquire sea ice data in all weather conditions, and it is a useful tool for monitoring sea ice conditions. In this paper, we combine a multi-layered sea ice electromagnetic (EM) scattering model with a sea ice thermodynamic model to assess the determination of the thickness of flat thin ice in the Bohai Sea using SAR at different frequencies, polarization, and incidence angles. Our modeling studies suggest that co-polarization backscattering coefficients and the co-polarized ratio can be used to retrieve the thickness of flat thin ice from C- and X-band SAR, while the co-polarized correlation coefficient can be used to retrieve flat thin ice thickness from L-, C-, and X-band SAR. Importantly, small or moderate incidence angles should be chosen to avoid the effect of speckle noise.展开更多
Over the past 20 years,sonar imaging technology particularly for the high-technology sector has been a focus of research,in which many developed countries,especially those with coast lines,have been competing with eac...Over the past 20 years,sonar imaging technology particularly for the high-technology sector has been a focus of research,in which many developed countries,especially those with coast lines,have been competing with each other.It has seen a rapid development with increasing widespread applications that has played an important and irreplaceable role in underwater exploration with great prospects for social,economic,scientific,and military benefits.The fundamental techniques underlying sonar imaging,including multi-beamforming,synthetic-aperture and inverse synthetic-aperture sonar,acoustic lensing,and acoustical holography,are described in this paper.This is followed by a comprehensive and systematic review on the advantages and disadvantages of these imaging techniques,applicability conditions,development trends,new ideas,new methods,and improvements in old methods over recent years with an emphasis on the situation in China,along with a bold and constructive prediction to some development characteristics of sonar imaging technology in the near future in China.The perspectives presented in this paper are offered with the idea of providing some degree of guidance and promotion of research on sonar imaging technology.展开更多
This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response ...This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response is given. The procedure for the squint mode airborne SAR processing using the two RD algorithms is outlined. The simulation demonstrates that these two RD algorithms are suitable for squint mode airborne SAR when the squint angle is not larger than 20(°).展开更多
Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth ...Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth signal in the squint SAR data processing, andthe different slant range targets have different Doppler frequencies. From the mathematicalmodel of SAR echo signal, this paper carefully analyzes the instantaneous azimuth frequency, theinstantaneous Doppler frequency component of the azimuth frequency and the impact of rangechirp on azimuth frequency, which explains that Doppler frequency should be properly selected forcorrect SAR imaging in the squint SAR. The results of point target simulation experiments showthat the way is reasonable for the squint SAR and can effectively complete range compressionand azimuth focusing, and improve images' quality.展开更多
Because texture images cannot be directly processed by the gray level information of individual pixel,we propose a new texture descriptor which reflects the intensity distribution of the patch centered at each pixel.T...Because texture images cannot be directly processed by the gray level information of individual pixel,we propose a new texture descriptor which reflects the intensity distribution of the patch centered at each pixel.Then the general multiphase image segmentation model of Potts model is extended for texture segmentation by adding the region information of the texture descriptor.A fast numerical scheme based on the split Bregman method is designed to speed up the computational process.The algorithm is efficient,and both the texture descriptor and the characteristic functions can be implemented easily.Experiments using synthetic texture images,real natural scene images and synthetic aperture radar images are presented to give qualitative comparisons between our method and other state-of-the-art techniques.The results show that our method can accurately segment object regions and is competitive compared with other methods especially in segmenting natural images.展开更多
In this paper,a focusing approach is presented to widen the use of efficient monostatic imaging algorithms for azimuth-invariant bistatic synthetic aperture radar(SAR) data.The bistatic range history is modeled by a p...In this paper,a focusing approach is presented to widen the use of efficient monostatic imaging algorithms for azimuth-invariant bistatic synthetic aperture radar(SAR) data.The bistatic range history is modeled by a polynomial of azimuth time.Using this model,an analytic form of the signal spectrum in the 2D frequency domain is derived,and a simple single-valued relation between the transmitter and receive ranges is established.In this way,a lot of monostatic image formation algorithms can be extended for the bistatic SAR data,and a bistatic chirp scaling algorithm is developed as an application of the new approach.This algorithm can be used to process the azimuth-invariant bistatic configuration where the transmitter and receiver platforms are moving on parallel tracks with the same velocity.In addition,some simulation results are given to demonstrate the validity of the proposed approach.展开更多
基金Supported by the Major Program of the National Natural Science Foundation of China(No.60890075)the National Natural Science Foundation of China for Young Scientists(No.40906093)
文摘Flat thin ice (<30 cm thick) is a common ice type in the Bohai Sea, China. Ice thickness detection is important to offshore exploration and marine transport in winter. Synthetic aperture radar (SAR) can be used to acquire sea ice data in all weather conditions, and it is a useful tool for monitoring sea ice conditions. In this paper, we combine a multi-layered sea ice electromagnetic (EM) scattering model with a sea ice thermodynamic model to assess the determination of the thickness of flat thin ice in the Bohai Sea using SAR at different frequencies, polarization, and incidence angles. Our modeling studies suggest that co-polarization backscattering coefficients and the co-polarized ratio can be used to retrieve the thickness of flat thin ice from C- and X-band SAR, while the co-polarized correlation coefficient can be used to retrieve flat thin ice thickness from L-, C-, and X-band SAR. Importantly, small or moderate incidence angles should be chosen to avoid the effect of speckle noise.
基金Supported by the National Natural Science Foundation of China(No.41076060)
文摘Over the past 20 years,sonar imaging technology particularly for the high-technology sector has been a focus of research,in which many developed countries,especially those with coast lines,have been competing with each other.It has seen a rapid development with increasing widespread applications that has played an important and irreplaceable role in underwater exploration with great prospects for social,economic,scientific,and military benefits.The fundamental techniques underlying sonar imaging,including multi-beamforming,synthetic-aperture and inverse synthetic-aperture sonar,acoustic lensing,and acoustical holography,are described in this paper.This is followed by a comprehensive and systematic review on the advantages and disadvantages of these imaging techniques,applicability conditions,development trends,new ideas,new methods,and improvements in old methods over recent years with an emphasis on the situation in China,along with a bold and constructive prediction to some development characteristics of sonar imaging technology in the near future in China.The perspectives presented in this paper are offered with the idea of providing some degree of guidance and promotion of research on sonar imaging technology.
文摘This paper studies two range-Doppler (RD) algorithms for the azimuth correlation in the squint mode airborne synthetic aperture radar (SAR). The modeling of squint mode airborne SAR spatial geometry and echo response is given. The procedure for the squint mode airborne SAR processing using the two RD algorithms is outlined. The simulation demonstrates that these two RD algorithms are suitable for squint mode airborne SAR when the squint angle is not larger than 20(°).
文摘Instantaneous Doppler frequency for squint SAR imaging has been found with ChirpScaling Algorithm (CSA). Because the azimuth sample is not perpendicular to the range sample,the range signal must impact on the azimuth signal in the squint SAR data processing, andthe different slant range targets have different Doppler frequencies. From the mathematicalmodel of SAR echo signal, this paper carefully analyzes the instantaneous azimuth frequency, theinstantaneous Doppler frequency component of the azimuth frequency and the impact of rangechirp on azimuth frequency, which explains that Doppler frequency should be properly selected forcorrect SAR imaging in the squint SAR. The results of point target simulation experiments showthat the way is reasonable for the squint SAR and can effectively complete range compressionand azimuth focusing, and improve images' quality.
基金supported by the National Natural Science Foundation of China(No.61170106)
文摘Because texture images cannot be directly processed by the gray level information of individual pixel,we propose a new texture descriptor which reflects the intensity distribution of the patch centered at each pixel.Then the general multiphase image segmentation model of Potts model is extended for texture segmentation by adding the region information of the texture descriptor.A fast numerical scheme based on the split Bregman method is designed to speed up the computational process.The algorithm is efficient,and both the texture descriptor and the characteristic functions can be implemented easily.Experiments using synthetic texture images,real natural scene images and synthetic aperture radar images are presented to give qualitative comparisons between our method and other state-of-the-art techniques.The results show that our method can accurately segment object regions and is competitive compared with other methods especially in segmenting natural images.
基金the National High Technology Research and Development Program (863) of China(No. 2008AA12Z108)
文摘In this paper,a focusing approach is presented to widen the use of efficient monostatic imaging algorithms for azimuth-invariant bistatic synthetic aperture radar(SAR) data.The bistatic range history is modeled by a polynomial of azimuth time.Using this model,an analytic form of the signal spectrum in the 2D frequency domain is derived,and a simple single-valued relation between the transmitter and receive ranges is established.In this way,a lot of monostatic image formation algorithms can be extended for the bistatic SAR data,and a bistatic chirp scaling algorithm is developed as an application of the new approach.This algorithm can be used to process the azimuth-invariant bistatic configuration where the transmitter and receiver platforms are moving on parallel tracks with the same velocity.In addition,some simulation results are given to demonstrate the validity of the proposed approach.
