Broadening circular and linear SAR image and 3D volume parameters for accurate localization

In this paper, we propose the two-dimensional imaging response of three-dimensional moving target via synthetic aperture radar (SAR) with back-projection imaging algorithm. Firstly, we analyzed the imaging response for each single echo, which is the intersection of Doppler isodop and iso-range contour. Then, we come up with a focus condition for moving target SAR imaging. Besides, we find that the Doppler frequency will cause a shift and the motion trail of moving target will draw a curve in the imaging result over synthetic aperture time. Meanwhile, we provide the numerical simulation experiments of moving point targets via linear SAR and circular SAR with X-band and THz-band, respectively, to verify the conclusion of moving target imaging response.

This paper studies the detection of rare earth elements (REEs) in groundwater and the intervention of dance training fatigue based on synthetic aperture radar (SAR) imaging algorithm. Among them, the radar 3D imaging technology is to add a new synthetic aperture in the direction perpendicular to the 2D SAR imaging plane, so that 3D imaging can be carried out. The two-dimensional SAR plane image is obtained by two-dimensional matched filtering of the echo signal. It is the result of the projection of the real three-dimensional space on the range azimuth plane. Each pixel value of the two-dimensional SAR plane image is the result of the superposition of all scattering points with different heights in the same range azimuth unit in the three-dimensional space. There are geometric distortions such as overlap, shadow and stretch, which results in the lack of three-dimensional information. Groundwater is the main water source of the plain, accounting for more than 70% of the total water supply. The study of evolution law of groundwater chemical composition based on SAR imaging algorithm is not only helpful to provide scientific data for the sustainable development and utilization of groundwater in plain, but also helpful to further understand the hydrogeochemical process of groundwater in plain. The spatial distribution, temporal development and REE distribution of the main components of shallow groundwater and deep groundwater in North China Plain were investigated. Finally, according to the theory of modern physiology and traditional medicine about the research results of sports burnout, this paper selects the university students who specialize in sports dance as the research object and uses the methods of literature, question table, interview and mathematical statistics to investigate. It can be found that among the three kinds of sports burnout, physical burnout starts first, and then visceral burnout, the last is the sense of mental weariness. There are some differences between boys and girls in fatigue parts. Modern dance is more likely to cause chronic fatigue than Latin dance.

The 3-D Fractional Fourier Transformation (FrFT) has unique applicability to multi-pass and multiple receiver Synthetic Aperture Radar (SAR) scenarios which can collect radar returns to create volumetric reflectivity data. The 3-D FrFT can independently compress and image radar data in each dimension for a broad set of parameters. The 3-D FrFT can be applied at closer ranges and over more aperture sampling conditions than other imaging algorithms. The FrFT provides optimal processing matched to the quadratic signal content in SAR (i.e. the pulse chirp and the spherical wave-front across the aperture). The different parameters for 3-D linear, circular, and orbital SAR case are derived and specifi…c considerations such as squint and scene extent for each scenario are addressed. Example imaged volumes are presented for linear, circular and orbital cases. The imaged volume is sampled in the radar coordinate system and can be transformed to a target based coordinate system. Advantages of the FrFT which extend to the 3-D FrFT include its applicability to a wide variety of imaging condition (standoff range and aperture sub-sampling) as well as inherent phase preservation in the images formed. The FrFT closely matches the imaging process and thus is able to focus SAR images over a large variation in standoff ranges specifi…cally at close range. The FrFT is based on the relationship between time and frequency and thus can create an image from an under-sampled wave-front. This ability allows the length of the synthetic aperture to be increased for a fixed number of aperture samples.

In this dissertation, several advancements in the field of synthetic aperture radar (SAR) polarimetry are described. First, a calibration technique for a dual-polarized antenna is developed, allowing polarimetric calibration to be performed through the measurement of specific square- or circular-waveguide loads, resulting in improvement in measurement accuracy when performing polarimetric SAR measurements. Imaging experiments are performed using a fabricated dual-polarized antenna and calibration loads, validating the efficacy of this calibration procedure. Second, a technique is developed enabling SAR polarimetric measurements to be made using a single polarization configuration, making use of the unique polarization pattern of a radially-polarized antenna. This technique possesses the full capabilities of previously used polarimetric SAR techniques, while at the same time vastly simplifies the necessary hardware and the calibration procedure. To this end, a specialized SAR imaging algorithm is developed, and imaging experiments are performed that demonstrate the effectiveness and accuracy of this technique compared to traditional SAR polarimetry methods. Third, a SAR 3D polarimetry technique is developed, by which targets can be characterized by their 3D features such as relative orientation about all three axes of rotation. A SAR imaging algorithm is developed for this purpose, and imaging experiments are performed to demonstrate the efficacy of the method. The advancements made in this work open the door for SAR polarimetry to be used in a much more diverse set of applications. Fourth, SAR polarimetry was applied to the specific nondestructive evaluation (NDE) application of detection and characterization of fiber misalignment in carbon and glass fiber polymer (CFRP and GFRP) composites. CFRP and GFRP samples are manufactured with fiber misalignment, and two different polarimetric SAR techniques, one of which is SAR 3D polarimetry, are used to detect the misalignment and determine the specific misalignment angles in each sample.

Synthetic Aperture Radar (SAR) is a powerful tool strongly employed in maritime monitoring and surveillance. Among different polarimetric SAR modes, dual-pol SAR data are widely used for monitoring large ocean and coastal areas. The degree of polarization (DoP) is a fundamental quantity characterizing a partially polarized electromagnetic field. The performance of the DoP is studied for ship detection under different polarizations in hybrid/compact and linear dual-pol SAR imagery. Experiments are performed on C-band polarimetric data acquired by RADARSAT-2 over San Francisco Bay and the Strait of Gibraltar.

The researches of imaging algorithms for synthetic aperture radar (SAR) is focused on the air- and space-borne SAR from the theory of SAR was formed . In this paper, we propose a modified frequency scaling algorithm for missile-borne SAR imaging. According to the characters of missile-borne SAR including high flight speed, non-straight movement with non-constant velocity and big squint angle, which forward a greater requirement for real time performance, precision of the motion compensation. On the base of the missile-borne SAR geometry, we described the complete derivation of the algorithm and the refined frequency scaling factors of each signal domain, the refined azimuth scaling factor can reduce azimuth time expansion and improve efficiency of azimuth processing. Then simulated the algorithm using Matlab programs in computer, analyzed the imaging result of the point target. And the simulation verified the algorithm is valid.

As having the imaging ability of area in front of flight direction, forward-looking synthetic aperture radar (SAR) has become a hot topic in areas of SAR research. Nevertheless, existing imaging algorithms of forward-looking SAR are all based on the assumption that the platform is moving in low velocity. When this assumption is not satisfied, the imaging result of existing algorithms will show focus out effect and deviation of imaging position from real position. Aiming at this problem and taking airborne forward-looking SAR system using single transmitting and multiple receiving antennas as the research object, this paper analyzes the feasibility of forward-looking SAR imaging of high velocity platform, and proposes a forward-looking SAR imaging algorithm suitable for high velocity platform according to its spatial geometry and the model of echo signal. Finally, the raw echo data of an array of point targets is simulated, and the focused images are obtained using the algorithm proposed in this paper. Imaging results demonstrate the validity of the algorithm. (6 pages)

Synthetic aperture radar (SAR) is a new high-tech radar that uses SAR principles and pulse compression technology to perform high-resolution imaging of ground targets. Because it is not affected by various factors such as location, time, and climate, it is widely used in the civilian and military fields, bringing huge social and economic benefits. Moreover, the environment of agricultural water resources and the development of regional agricultural economy can be studied using the SAR imaging algorithm. With the serious shortage of water resources and the increase of the world’s population, the use of water resources for agriculture must not only achieve the goal of saving water, but more importantly, achieve efficient production on the premise of saving water. However, the shortage of water resources in China has become a serious constraint on the development of agriculture and rural economy and has become an important factor restricting the sustainable development of agriculture and rural economy. Therefore, the development of efficient and sustainable use of water resources is very important to establish a water-saving society for the sustainable development of China’s economy and society. For the spaceborne SAR system, an azimuth-based multi-channel range ambiguity suppression method is proposed in this chapter. The simulation results show that after adopting the azimuth phase encoding technology, the azimuth spectrum of the signal in the ambiguous area can be moved to suppress the distance ambiguity.

Although Synthetic Aperture Radar (SAR) can capture rich land cover information as a most important advanced technique in the field of international earth observation, the application effects still limited significantly. The reason is that the study of SAR imaging processing, SAR image processing and SAR applications are conducted respectively, the integrated study are lacked for parameter selection of SAR imaging processing and SAR image processing and targets identification of SAR application. Focusing on above science problems, the study for phase high fidelity model of high precision interferometric SAR, SAR non-stationary backscattering characteristics and cognition, SAR three-dimensional electromagnetic scattering modeling and its scattering mechanism and SAR multi-parameters optimization information extraction has been conducted. The typical natural distributed targets and man-made targets such as surface deformation, sea ice, building complex and collapsed building are selected, the method and application study oriented to SAR environmental parameters inversion are conduced, the main result and conclusion are as follows: (1) The overall theoretical frames of SAR information integrated processing was proposed; The simulation and ground validation system used to assess the effects of SAR information integrated processing was created; furthermore, the spaceborne SAR imaging algorithm with three steps focusing processing was proposed and realized the multi-modal integrated imaging processing and improved the imaging processing precision. (2) In terms of SAR information integrated processing of natural targets, focusing on phase high fidelity imaging processing of interferometric SAR surface deformation monitoring, an novel spaceborne SAR high fidelity simulation method based on stationary RCS and improved Goldstein SAR interferogram filter based on empirical mode decomposition were proposed. Focusing on multi-parameters optimization processing of sea ice types classification, the multi-channel spaceborne SAR sparse imaging method based on compressive sensing, Kalman filter for removal of scalloping and inter-scan banding in ScanSAR images and SVM sea ice classification method combined with sea ice concentration were proposed. (3) In terms of SAR information integrated processing of man-made targets, focusing on non-stationary backscattering from building complex, mitigation of azimuth ambiguities in spaceborne stripmap SAR iamges using selective restoration, SAR image despeckling by selective 3D filtering of multiple compressive reconstructed images and man-made target detection in urban areas based on a new azimuth stationary extraction method were proposed. Focusing on three-dimensional modeling and fast extraction of collapsed building, H-a-p method used for collapsed building extraction was proposed.

This paper deals with the issue of ground moving target imaging and motion parameter estimation with an airborne dual-channel circular stripmap synthetic aperture radar (CSSAR) system. Although several methods of ground moving target motion parameter estimation have been proposed for the conventional airborne linear stripmap SAR, they cannot be applied to airborne CSSAR because the range history of a ground moving target for airborne CSSAR is different than that for airborne linear stripmap SAR. In this paper, the moving target’s range history for airborne dual-channel CSSAR and the target signal model after the displaced phase center antenna processing are derived, and a new ground moving target imaging and motion parameter estimation algorithm is developed. In this algorithm, the estimation of baseband Doppler centroid and its compensation are first performed. Then focusing is implemented in the 2-D frequency domain via phase multiplication, and the target is focused in the SAR image without azimuth displacement due to the compensation of the Doppler shift caused by its motion. Finally, the target’s motion parameters are estimated with its Doppler parameters and its position in the SAR image. Numerical simulations are conducted to validate the derived range history and the performance of the proposed algorithm.

Snow water equivalent (SWE) is an important surface parameter for understanding a number of Earth system processes. Synthetic aperture radar (SAR) has considerable potential for measuring SWE of dry-snow because SAR can penetrate through the snow to the ground surface and is both amplitude- and phase-sensitive to refraction from the snow. Previous work on refraction-based SWE measurement by SAR has utilized the repeat-pass InSAR phase signal to estimate changes in SWE that occur between SAR acquisitions. These are subject to temporal decorrelation effects and consider only the refraction that occurs along the SAR beam center rather than the entire synthetic aperture. This study examines the refractive effect of dry-snow along the synthetic aperture and its impact on SAR image formation including defocusing and phase bias of the system impulse response. Snow phase compensation during time domain processing to recover the snow-free impulse response function (IRF) is described and demonstrated. The feasibility of using the mapdrift and image sharpness autofocus methods to estimate SWE is examined, and the effect of key system parameters on the estimation performance is derived. Experimental validation of the method was conducted by acquiring L-band data with the Simon Fraser University (SFU) Airborne SAR System over a pair of corner reflectors installed on the Kluane icefield in northwestern Canada. Results from both simulations and the icefield experiment are presented and compared including an analysis of errors affecting the estimation.

As important man-made targets, bridges have been a major focus of Synthetic Aperture Radar (SAR) image interpretation, and many researchers have developed methods for bridge detection. The core frameworks of these methods are analogical, a river is first extracted, and a water bridge is detected based on the positional relationship between the river and bridge. However, existing bridge detection methods relying on river extraction; cannot be utilized detect land bridges. This is because the background environment under a bridge is land, not river, which has different scattering characteristics and shape layouts. As such, the traditional method for extracting rivers is not suitable for extracting land background, and it is impossible to locate a bridge based on prior knowledge of its location of. To resolve this problem, in this study, we propose a land bridge detection method based on polarized Circular SAR (CSAR) images. In our proposed method, the Circular Polarization Entropy (CPE) of an observed scene is introduced to separate possible bridge targets from a land background (In our experiment, the average CPE of the bridge is 0.4018, and that of the land background is 0.7819; thus there is a clear difference between the bridge and background). False targets are removed based on the difference in the polarization entropy variance features of the bridges and other ground objects; and the size characteristics of the bridges. Finally, accurate extractions of land bridges are obtained based on the geometric characteristics of the bridges. Experimental results based on real airborne L-band polarized CSAR data verify the correctness of the theoretical analysis and effectiveness of the proposed method.

This article presents a synthetic aperture radar (SAR) imaging algorithm based on a compressed sensing (CS) reconstruction approach, which is suitable for the detection of foreign object debris (FOD) located in a multilayered circular dielectric structure for nondestructive testing (NDT) application. The method proposed considers the refraction model at the boundaries between each two adjacent layers. This method is different from free space as imaging background assumption in previous CS-based SAR imaging applications. In addition, the prior information that the FOD is displayed with a sparse distribution is applied. Therefore, the method proposed could obtain better focus on effectiveness than time-reversal imaging algorithm with the same measurement points. Further, the CST simulations and the experiment were conducted by taking two small metallic targets as FOD embedded in the three-layered circular dielectric structure. The results of simulations and experiment demonstrated that the proposed method has better effect than previous methods.

In synthetic aperture radar (SAR) imaging, geometric resolution, sidelobe level (SLL) and signal-to-noise ratio (SNR) are the most important parameters for measuring the SAR image quality. The staring spotlight mode continuously transmits signals to a fixed area by steering the azimuth beam to acquire azimuth high geometric resolution, and its two-dimensional (2D) impulse response with the low SLL is usually obtained from the 2D weighted power spectral density (PSD) by the selected weighting window function. However, this results in the SNR reduction due to 2D amplitude window weighting. In this paper, the staring spotlight SAR with nonlinear frequency modulation (NLFM) signal and azimuth non-uniform sampling (ANUS) is proposed to obtain high geometric resolution SAR images with the low SLL and almost without any SNR reduction. The NLFM signal obtains non-equal interval frequency sampling points under uniform time sampling by adjusting the instantaneous chirp rate. Its corresponding PSD is similar to the weighting window function, and its pulse compression result without amplitude window weighting has low sidelobes. To obtain a similar Doppler frequency distribution for low sidelobe imaging in azimuth, the received SAR echoes are designed to be non-uniformly sampled in azimuth, in which the sampling sequence is dense in middle and sparse in both ends, and azimuth compression result with window weighting would also have low sidelobes. According to the echo model of the proposed imaging mode, both the back projection algorithm (BPA) and range migration algorithm (RMA) are modified and presented to handle the raw data of the proposed imaging mode. Both imaging results on simulated targets and experimental real SAR data processing results of a ground-based radar validate the proposed low sidelobe imaging mode.

Array synthetic aperture radar (SAR) is one of the hot areas in radar imaging field because of its three-dimensional (3-D) imaging ability. Combining the advantages of linear array SAR in aspect of side-lobe suppression and circular SAR in aspect of high resolution, a new kind of annular array synthetic aperture radar (AASAR) mode is employed for 3-D microwave imaging. Based on the mathematical derivation of AASAR model, the sparse layout of the annular array in the cross-track direction can acquire 3-D high resolution and effective side-lobe suppression ability. Then on this basis, a proto-type AASAR experiment system is built, and some 3-D AASAR imaging outdoor experiments are conducted. Through the experiment result, the validity of 3-D AASAR imaging can be demonstrated.