scholarly journals Airborne SAR Imaging Algorithm for Ocean Waves Based on Optimum Focus Setting

2019 ◽  
Vol 11 (5) ◽  
pp. 564 ◽  
Author(s):  
Xiangfei Wei ◽  
Jinsong Chong ◽  
Yawei Zhao ◽  
Yan Li ◽  
Xiaonan Yao
Keyword(s):  
Surface Waves ◽  
Phase Speed ◽  
Ocean Waves ◽  
Integration Time ◽  
Sar Image ◽  
Sar Images ◽  
Imaging Algorithm ◽  
Dominant Wave ◽  
Sar Imaging ◽  
Airborne Sar

Ocean waves are the richest texture on the sea surface, from which valuable information can be inversed. In general, the Synthetic Aperture Radar (SAR) images of surface waves will inevitably be distorted due to the intricate motion of surface waves. However, commonly used imaging algorithms do not take the motion of surface waves into consideration. Therefore, surface waves on the obtained SAR images are rather blurred. To solve this problem, an airborne SAR imaging algorithm for ocean waves based on optimum focus setting is proposed in this paper. Firstly, in order to obtain the real azimuth phase speed of dominant wave, the geometric and scanning distortion in the blurred SAR image is calibrated. Subsequently, according to the SAR integration time and wavelength of the dominant wave, a proper focus setting variation section is selected. Afterwards, all the focus settings in this variation section are used to refocus the image, which are then compared to decide the optimum focus setting for dominant wave. Finally, by redesigning the azimuth matched filter using this optimum focus setting, a well-focused SAR image for the dominant wave can be obtained. The proposed algorithm is applied to both simulation and field data, and SAR images of surface waves are obtained. Furthermore, the obtained images are compared with those obtained with a zero-focus setting. The comparison shows that the focus of surface waves is significantly improved, which verifies the effectiveness of the proposed algorithm. Finally, how to choose the appropriate focus setting variation section under different parameters and the applicability of the algorithm are analyzed.

scholarly journals Similarity measures of full polarimetric SAR images fusion for improved SAR image matching

2015 ◽  
Vol XL-7/W4 ◽  
pp. 13-16 ◽  
Author(s):  
H. Ding
Keyword(s):  
Similarity Measure ◽  
Image Matching ◽  
Stereo Matching ◽  
Similarity Measures ◽  
Sar Image ◽  
Polarimetric Sar ◽  
Sar Images ◽  
Sar Data ◽  
Sar Imagery ◽  
Airborne Sar

China’s first airborne SAR mapping system (CASMSAR) developed by Chinese Academy of Surveying and Mapping can acquire high-resolution and full polarimetric (HH, HV, VH and VV) Synthetic aperture radar (SAR) data. It has the ability to acquire X-band full polarimetric SAR data at a resolution of 0.5m. However, the existence of speckles which is inherent in SAR imagery affects visual interpretation and image processing badly, and challenges the assumption that conjugate points appear similar to each other in matching processing. In addition, researches show that speckles are multiplicative speckles, and most similarity measures of SAR image matching are sensitive to them. Thus, matching outcomes of SAR images acquired by most similarity measures are not reliable and with bad accuracy. Meanwhile, every polarimetric SAR image has different backscattering information of objects from each other and four polarimetric SAR data contain most basic and a large amount of redundancy information to improve matching. Therefore, we introduced logarithmically transformation and a stereo matching similarity measure into airborne full polarimetric SAR imagery. Firstly, in order to transform the multiplicative speckles into additivity ones and weaken speckles' influence on similarity measure, logarithmically transformation have to be taken to all images. Secondly, to prevent performance degradation of similarity measure caused by speckles, measure must be free or insensitive of additivity speckles. Thus, we introduced a stereo matching similarity measure, called Normalized Cross-Correlation (NCC), into full polarimetric SAR image matching. Thirdly, to take advantage of multi-polarimetric data and preserve the best similarity measure value, four measure values calculated between left and right single polarimetric SAR images are fused as final measure value for matching. The method was tested for matching under CASMSAR data. The results showed that the method delivered an effective performance on experimental imagery and can be used for airborne SAR matching applications.

scholarly journals Indoor Experiments of Bistatic/Multistatic GB-SAR with One-Stationary and One-Moving Antennae

2021 ◽  
Vol 13 (18) ◽  
pp. 3733
Author(s):  
Hoonyol Lee ◽  
Jihyun Moon
Keyword(s):  
Time Domain ◽  
Speckle Noise ◽  
The Other ◽  
Synthetic Aperture ◽  
Sar Image ◽  
Sar Images ◽  
Airborne Sar ◽  
Transmitting Antenna ◽  
Azimuth Resolution ◽  
Ku Band

Ground-based synthetic aperture radar (GB-SAR) is a useful tool to simulate advanced SAR systems with its flexibility on RF system and SAR configuration. This paper reports an indoor experiment of bistatic/multistatic GB-SAR operated in Ku-band with two antennae: one antenna was stationary on the ground and the other was moving along a linear rail. Multiple bistatic GB-SAR images were taken with various stationary antenna positions, and then averaged to simulate a multistatic GB-SAR configuration composed of a moving Tx antenna along a rail and multiple stationary Rx antennae with various viewing angles. This configuration simulates the use of a spaceborne/airborne SAR system as a transmitting antenna and multiple ground-based stationary antennae as receiving antennae to obtain omni-directional scattering images. This SAR geometry with one-stationary and one-moving antennae configuration was analyzed and a time-domain SAR focusing algorithm was adjusted to this geometry. Being stationary for one antenna, the Doppler rate was analyzed to be half of the monostatic case, and the azimuth resolution was doubled. Image quality was enhanced by identifying and reducing azimuth ambiguity. By averaging multiple bistatic images from various stationary antenna positions, a multistatic GB-SAR image was achieved to have better image swath and reduced speckle noise.

An Efficient Segmentation Method for Mariculture Areas on Airborne SAR Images

2019 ◽  
Vol 53 (3) ◽  
pp. 30-38
Author(s):  
Houjun Wang ◽  
Hui Liu ◽  
Ning Ding ◽  
Pingping Jing ◽  
Guangyu Li
Keyword(s):  
Image Data ◽  
Synthetic Aperture ◽  
Sar Image ◽  
Adaptive Segmentation ◽  
Segmentation Method ◽  
Clustering Method ◽  
Sar Images ◽  
Local Patch ◽  
Airborne Sar ◽  
Coarse To Fine

AbstractIn this paper, the problems of mariculture area segmentation and corresponding area value estimations are investigated on the basis of airborne synthetic aperture radar (SAR) images. In order to deal with a limited amount of noisy airborne SAR image data in an efficient way, an effective coarse-to-fine approach is proposed, consisting of three major components, including (1) an adaptive segmentation method for each local patch to remove noise from the ocean background, (2) a dynamic coarse-to-fine clustering method for grouping pixels to achieve image segments, and (3) a polygon-fitting-based algorithm to obtain regular borders for each region and corresponding area value. Some feasible experiments are operated based on the restricted airborne SAR images, and the effectiveness of the proposed algorithm is validated in terms of the provided pixel level evaluation annotations.

Design, Deploy and Signal Analysis of Different Types of CR

2012 ◽  
Vol 239-240 ◽  
pp. 1238-1241
Author(s):  
Jing Hui Fan ◽  
Hong Li Zhao ◽  
Yi Wang
Keyword(s):  
Data Processing ◽  
Signal Analysis ◽  
Corner Reflector ◽  
Sar Image ◽  
Sar Images ◽  
Differential Processing ◽  
Imaging Parameters ◽  
Sar Imaging ◽  
Different Types ◽  
Reflection Intensity

In Shuping area, it is difficulty to find enough nature coherent targets to use InSAR technique to monitor the landslide. In order to solve the problem, CRs(Corner Reflectors) were used to improve the effectiveness of this technology. In this article Pyramidal Corner Reflector, Asymmetric Cubic Corner Reflector, Double Direction Asymmetric Cubic Corner Reflector are designed. In order to achieve maximum reflection intensity of CR, it's attitude must be carefully adjusted to match with the SAR imaging parameters exactly. After the CRs were deployed, the strong echo signals can be retrieved from SAR images. Analyzing the SAR image peak signals to locate the CR is the premise of differential processing. Through image location and phase analysis of ASAR and RADARSAT-2, the CRs’ signals can be recognition certainly. During the data processing of ASAR and PALSAR, the CRs can be regarded as ideal coherence target points.

scholarly journals A New Synthetic Aperture Radar (SAR) Imaging Method Combining Match Filter Imaging and Image Edge Enhancement

Sensors ◽  
2018 ◽  
Vol 18 (12) ◽  
pp. 4133 ◽  
Author(s):  
Bing Sun ◽  
Chuying Fang ◽  
Hailun Xu ◽  
Anqi Gao
Keyword(s):  
Image Processing ◽  
Image Segmentation ◽  
Synthetic Aperture Radar ◽  
Synthetic Aperture ◽  
Imaging Method ◽  
Sar Image ◽  
Sar Images ◽  
Gradient Operator ◽  
Sar Imaging ◽  
Aperture Radar

In general, synthetic aperture radar (SAR) imaging and image processing are two sequential steps in SAR image processing. Due to the large size of SAR images, most image processing algorithms require image segmentation before processing. However, the existence of speckle noise in SAR images, as well as poor contrast and the uneven distribution of gray values in the same target, make SAR images difficult to segment. In order to facilitate the subsequent processing of SAR images, this paper proposes a new method that combines the back-projection algorithm (BPA) and a first-order gradient operator to enhance the edges of SAR images to overcome image segmentation problems. For complex-valued signals, the gradient operator was applied directly to the imaging process. The experimental results of simulated images and real images validate our proposed method. For the simulated scene, the supervised image segmentation evaluation indexes of our method have more than 1.18%, 11.2% and 11.72% improvement on probabilistic Rand index (PRI), variability index (VI), and global consistency error (GCE). The proposed imaging method will make SAR image segmentation and related applications easier.

scholarly journals Refocusing Moving Ship Targets in SAR Images Based on Fast Minimum Entropy Phase Compensation

Sensors ◽  
2019 ◽  
Vol 19 (5) ◽  
pp. 1154 ◽  
Author(s):  
Xiangli Huang ◽  
Kefeng Ji ◽  
Xiangguang Leng ◽  
Ganggang Dong ◽  
Xiangwei Xing
Keyword(s):  
Synthetic Aperture Radar ◽  
Phase Error ◽  
Synthetic Aperture ◽  
Sar Image ◽  
Minimum Entropy ◽  
Sar Images ◽  
Phase Compensation ◽  
Translation Motion ◽  
Airborne Sar ◽  
Aperture Radar

Moving ship targets appear blurred and defocused in synthetic aperture radar (SAR) images due to the translation motion during the coherent processing. Motion compensation is required for refocusing moving ship targets in SAR scenes. A novel refocusing method for moving ship is developed in this paper. The method is exploiting inverse synthetic aperture radar (ISAR) technique to refocus the ship target in SAR image. Generally, most cases of refocusing are for raw echo data, not for SAR image. Taking into account the advantages of processing in SAR image, the processing data are SAR image rather than raw echo data in this paper. The ISAR processing is based on fast minimum entropy phase compensation method, an iterative approach to obtain the phase error. The proposed method has been tested using Spaceborne TerraSAR-X, Gaofeng-3 images and airborne SAR images of maritime targets.

scholarly journals Sea Spike Suppression Method Based on Optimum Polarization Ratio in Airborne SAR Images

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 3269
Author(s):  
Yawei Zhao ◽  
Jinsong Chong ◽  
Yan Li ◽  
Kai Sun ◽  
Xue Yang
Keyword(s):  
Target Detection ◽  
Oil Spills ◽  
Image Interpretation ◽  
Ocean Waves ◽  
Polarization Ratio ◽  
Sar Images ◽  
Difference Image ◽  
Suppression Method ◽  
Sar Data ◽  
Airborne Sar

In the condition of ocean observation for high-resolution airborne synthetic aperture radar (SAR), sea spikes will cause serious interference to SAR image interpretation and marine target detection. In order to improve the ability of target detection, it is necessary to suppress sea spikes in SAR images. However, there is no report on sea spike suppression methods in SAR images. As a step forward, a sea spike suppression method based on optimum polarization ratio in airborne SAR images is proposed in this paper. This method is only applicable to the situation where VV and HH dual-polarized SAR data containing sea spikes are acquired at the same time. By calculating the optimum polarization ratio, this method further obtains the difference image of the panoramic area accomplishing sea spike suppression. This method is applied to a field airborne X-band SAR data, including ocean waves, oil spills and ships. The results show that the sea spikes are well suppressed, the contrast of ocean waves and the contrast of oil spills are improved, and the false alarm rate of ship detection is reduced. The discussions on these results demonstrate that the proposed method can effectively suppress sea spikes and improve the interpretability of SAR images.

scholarly journals Method of airborne SAR image match integrating multi-information for block adjustment

2015 ◽  
Vol XL-7/W4 ◽  
pp. 191-195
Author(s):  
S. C. Yang ◽  
G. M. Huang ◽  
Z. Zhao ◽  
L. J. Lu
Keyword(s):  
Image Matching ◽  
Feature Detection ◽  
Sar Image ◽  
Image Block ◽  
Geometric Information ◽  
Sar Images ◽  
Image Match ◽  
Related Information ◽  
Grid Points ◽  
Airborne Sar

For the automation of SAR image Block Adjustment, this paper proposed a method of SAR image matching integrating multiinformation. It takes full advantage of SAR image geometric information, feature information, gray-related information and external auxiliary terrain information for SAR image matching. And then Image Tie Points (ITPs) of Block Adjustment can be achieved automatically. The main parts of extracting ITPs automatically include: First, SAR images were rectified geometrically based on the geometric information and external auxiliary terrain information (existed DEM) before match. Second, ground grid points with a certain interval can be get in the block area and approximate ITPs were acquired based on external auxiliary terrain information. Then match reference point was extracted for homologous image blocks with Harris feature detection operator and ITPs were obtained with pyramid matching based on gray-related information. At last, ITPs were transferred from rectified images to original SAR images and used in block adjustment. In the experiment, X band airborne SAR images acquired by Chinese airborne SAR system – CASMSAR system were used to make up the block. The result had showed that the method is effective for block adjustment of SAR data.

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