Weighted-elastic-wave interferometric imaging of microseismic source location

Knowledge of the locations of seismic sources is critical for microseismic monitoring. Time-window-based elastic wave interferometric imaging and weighted- elastic-wave （WEW） interferometric imaging are proposed and used to locate modeled microseismic sources. The proposed method improves the precision and eliminates artifacts in location profiles. Numerical experiments based on a horizontally layered isotropic medium have shown that the method offers the following advantages： It can deal with Iow-SNR microseismic data with velocity perturbations as well as relatively sparse receivers and still maintain relatively high precision despite the errors in the velocity model. Furthermore, it is more efficient than conventional traveltime inversion methods because interferometric imaging does not require traveltime picking. Numerical results using a 2D fault model have also suggested that the weighted-elastic-wave interferometric imaging can locate multiple sources with higher location precision than the time-reverse imaging method.

Three-dimensional bistatic interferometric ISA Rimaging

An approach based on interferometry technique is proposed for three-dimensional （3D） bistatic inverse synthetic aperture radar （ISAR） imaging. It is converted to a monostatic problem by using the theory that a bistatic radar equals a monostatic radar located on the bisector of bistatic an- gle. Then, interferometric phases extracted from a pair of cross shaped antennas are used to esti- mate the height and associated rotational velocity. Finally, numerical simulations are provided to e- valuate this method.

A Hierarchical Method for Locating the Interferometric Fringes of Celestial Sources in the Visibility Data

In source detection in the Tianlai project,locating the interferometric fringe in visibility data accurately will influence downstream tasks drastically,such as physical parameter estimation and weak source exploration.Considering that traditional locating methods are time-consuming and supervised methods require a great quantity of expensive labeled data,in this paper,we first investigate characteristics of interferometric fringes in the simulation and real scenario separately,and integrate an almost parameter-free unsupervised clustering method and seeding filling or eraser algorithm to propose a hierarchical plug and play method to improve location accuracy.Then,we apply our method to locate single and multiple sources’interferometric fringes in simulation data.Next,we apply our method to real data taken from the Tianlai radio telescope array.Finally,we compare with unsupervised methods that are state of the art.These results show that our method has robustness in different scenarios and can improve location measurement accuracy effectively.

SDOCT IMAGE RECONSTRUCTION BY INTERFEROMETRIC SYNTHETIC APERTURE MICROSCOPY

Spectral domain optical coherence tomography(SDOCT)is a noninvasive,cross-sectional imaging technique that measures depth resolved reflectance of tissue by Fourier transforming the spectral interferogram with the scanning of the reference avoided.Interferometric synthetic aperture microscopy(ISAM)is an optical microscopy computed-imaging technique for measuring the optical properties of biological tissues,which can overcome the compromise between depth of focus and transverse resolution.This paper describes the principle of SDOCT and ISAM,which multiplexes raw acquisitions to provide quantitatively meaningful data with reliable spatially invariant resolution at all depths.A mathematical model for a coherent microscope with a planar scanning geometry and spectral detection was described.The two-dimensional fast Fourier transform(FFT)of spectral data in the transverse directions was calculated.Then the nonuniform ISAM resampling and filtering was implemented to yield the scattering potential within the scalar model.Inverse FFT was used to obtain the ISAM reconstruction.One scatterer,multiple scatterers,and noisy simulations were implemented by use of ISAM to catch spatially invariant resolution.ISAM images were compared to those obtained using standard optical coherence tomography(OCT)methods.The high quality of the results validates the rationality of the founded model and that diffraction limited resolution can be achieved outside the focal plane.

Application of Seismic Interferometric Migration for Shallow Seismic High Precision Data Processing: A Case Study in the Shenhu Area

The stability of submarine geological structures has a crucial influence on the construction of offshore engineering projects and the exploitation of seabed resources. Marine geologists should possess a detailed understanding of common submarine geological hazards. Current marine seismic exploration methods are based on the most effective detection technologies. Therefore, current research focuses on improving the resolution and precision of shallow stratum structure detection methods. In this article, the feasibility of shallow seismic structure imaging is assessed by building a complex model, and differences between the seismic interferometry imaging method and the traditional imaging method are discussed. The imaging effect of the model is better for shallow layers than for deep layers because coherent noise produced by this method can result in an unsatisfactory imaging effect for deep layers. The seismic interference method has certain advantages for geological structural imaging of shallow submarine strata, which indicates continuous horizontal events, a high resolution, a clear fault, and an obvious structure boundary. The effects of the actual data applied to the Shenhu area can fully illustrate the advantages of the method. Thus, this method has the potential to provide new insights for shallow submarine strata imaging in the area.

Adaptive scale model reconstruction for radio synthesis imaging

A sky model from CLEAN deconvolution is a particularly effective high dynamic range reconstruction in radio astronomy,which can effectively model the sky and remove the sidelobes of the point spread function(PSF)caused by incomplete sampling in the spatial frequency domain.Compared to scale-free and multi-scale sky models,adaptive-scale sky modeling,which can model both compact and diffuse features,has been proven to have better sky modeling capabilities in narrowband simulated data,especially for large-scale features in high-sensitivity observations which are exactly one of the challenges of data processing for the Square Kilometre Array(SKA).However,adaptive scale CLEAN algorithms have not been verified by real observation data and allow negative components in the model.In this paper,we propose an adaptive scale model algorithm with non-negative constraint and wideband imaging capacities,and it is applied to simulated SKA data and real observation data from the Karl G.Jansky Very Large Array(JVLA),an SKA precursor.Experiments show that the new algorithm can reconstruct more physical models with rich details.This work is a step forward for future SKA image reconstruction and developing SKA imaging pipelines.

Novel reference range selection method in InISAR imaging

Aiming at the reference range selection for different antennas in interferometric inverse synthetic aperture radar （InlSAR） systems, this paper proposes a respective focusing （RF） method. The reference ranges for echoes of different antennas are selected respectively for RF, which is different from the traditional uniform focusing （UF） with the same reference range applied to all the antennas. First, a comparison between UF and RF for InlSAR signal model considering the ranging error is given. Compared with RF, UF has an advantage in overcoming the ranging error differences between different antennas. Then the influence of ranging error upon the interferometric imaging with RF is investigated particularly, and it is found that the ranging error differences between different antennas are far smaller than the wavelength, which is advantageous to imaging. By comparing the capabilities of inter- ferometric imaging between RF and UF, it is concluded that RF is a better choice in conquering problems such as image mismatching and phase ambiguity even with ranging errors. Simulations demonstrate the validity of the proposed method.

IMPACT OF WIDE-BAND I/Q MODULATION ERRORS IN SAR IMAGING ANALYSIS AND COMPENSATION METHOD RESAERCH

Direct quadrature modulation technology is suitable for wide-band radar signal generation. However, this method has rigorous requirements on amplitude and phase balance of the orthogonal input signals. If the requirements are not satisfied, there would be modulation errors such as image frequency and oscillator leakage that cannot be filtered. The modulation errors will therefore raise the noise floor of the range profile and reduce the dynamic range of the Synthetic Aperture Radar (SAR) image as a whole. In this paper, the wide-band In-phase/Quadrature-phase (I/Q) modulation errors are modeling analyzed, and the influence of wide-band I/Q modulation errors on SAR imaging is discussed. Furthermore, a compensation method of modulation errors is proposed, and the circuit implementation of the radar signal generation and pre-distortion is presented. The experimental results illustrate that the curves of the I/Q amplitude and phase imbalance errors are successfully extracted and the rejection of image frequency improved significantly, thus meets the requirements of the SAR imaging.

Effect of orbital errors on the geosynchronous circular synthetic aperture radar imaging and interferometric processing

The geosynchronous circular synthetic aperture radar (GEOCSAR) is an innovative SAR system,which can produce high resolution three-dimensional (3D) images and has the potential to provide 3D deformation measurement.With an orbit altitude of approximately 36 000 km,the orbit motion and orbit disturbance effects of GEOCSAR behave differently from those of the conventional spaceborne SAR.In this paper,we analyze the effects of orbit errors on GEOCSAR imaging and interferometric processing.First,we present the GEOCSAR imaging geometry and the orbit errors model based on perturbation analysis.Then,we give the GEOCSAR signal formulation based on imaging geometry,and analyze the effect of the orbit error on the output focused signal.By interferometric processing on the 3D reconstructed images,the relationship between satellite orbit errors and the interferometric phase is deduced.Simulations demonstrate the effects of orbit errors on the GEOCSAR images,interferograms,and the deformations.The conclusions are that the required relative accuracy of orbit estimation should be at centimeter level for GEOCSAR imaging at L-band,and that millimeter-scale accuracy is needed for GEOCSAR interferometric processing.

Imaging algorithm for synthetic aperture interferometric radiometer in near field

With the benefits of digital IC technology development, the synthetic aperture interferometric radiometer (SAIR) technique is growing fast and expanding to more and more application areas. The near field imaging detection is a potential application which has received increasing demand recently. Because the Fourier imaging theory of the traditional SAIR is based on far-field approximation, it will be invalid for near-field condition. This paper is devoted to establishing a new accurate imaging algorithm for near-field SAIR imaging. Firstly, the visibility function in near field is deduced and the relationship of which to far-field visibility function is analyzed. Then, a numerical method based on pseudo inverse and focal plane approximation is developed. The effectivity of this method is tested with imaging simulation of point source and extended source, and the superiority is also demonstrated by comparing with the existing phase-modified Fourier transform method. At last, the field experiment with one-dimensional SAIR instrument is performed to validate the practical feasibility of this method.

Inclusion of the tunneling phase shift for interferometric particle imaging for bubble sizing

The interferometric particle imaging technique makes use of the angular oscillations of the scattered light in the forward direction for droplet or bubble sizing.The out-of-focus image consists of fringes,the spacing of which reflects the interference between the surface-reflected light and the twofold-refracted light.Total internal reflection occurs when the incident light hits the bubble at a large incident angle.The tunneling phase shift is not included in the geometric optics approximation,which leads to a deviation from Mie theory.In this work,we modified the formula for describing the fringe spacing by including the tunneling phase shift of total internal reflection.Numerical analysis and experiments showed that the modification is effective for the measurement of bubbles smaller than 60μm.

MAXIMUM LIKELIHOOD ESTIMATION FOR INSAR IMAGE CO-REGISTRATION

This paper presents a closed-form robust phase correlation based algorithm for performing image registration to subpixel accuracy.The subpixel translational shift information is directly obtained from the phase of the normalized cross power spectrum by using Maximum Likelihood Estimation(MLE).The proposed algorithm also has slighter time complexity.Experimental results show that the proposed algorithm yields superior registration precision on the Cramér-Rao Bound(CRB) in the presence of aliasing and noise.

SAR Image Coregistration Using Fringe Definition Detection

In order to overcome the limitation of cross correlation coregistration method for Synthetic Aperture Radar （SAR） interferometric pairs with low coherence, a new image coregistration algorithm based on Fringe Definition Detection （FDD） is presented in this paper. The Fourier transformation was utilized to obtain spectrum characteristics of interferometric fringes. The ratio between spectrum mean and peak was proposed as the evaluation index for identifying homologous pixels from interferometric images. The satellites ERS-1/2 C-band SAR acquisitions covering the Yangtze River plain delta, eastern China and ALOS/PALSAR L-band images over the Longmen Shan mountainous area, southwestern China were respectively employed in the experiment to validate the proposed coregistration method. The testing results suggested that the derived Digital Elevation Model （DEM） from FDD method had good agreement with that from the cross correlation method as well as the reference DEM at high coherence area. However, The FDD method achieved a totally improved topographic mapping accuracy by 24 percent in comparison to the cross correlation method. The FDD method also showed better robustness and achieved relatively higher performance for SAR image eoregistration in mountainous areas with low coherence.

基于染色算法的地震干涉成像技术

为了提高基于染色算法的逆时偏移计算效率,提出基于染色算法的地震干涉成像技术(CC-STRTM)。地震干涉技术作为一种炮记录的处理手段可以消去两个炮记录中相同的信号。该技术将观测系统从地表下移到人为选取的地下校准面,将研究区域缩小到校准面下侧。再分析干涉成像结果,选出染色区域。最后完成复数域的逆时偏移处理,输出虚部偏移结果。通过复杂模型对该方法进行测试,对比分析成像结果和计算效率。结果表明,该方法在提高成像精度的同时不降低计算效率。

基于T型透镜排布的多频干涉系统设计及成像

为探究多频点采集对成像的影响,提出并搭建了一种T型透镜排布的多频干涉系统,该系统可以同时对二维光栅目标的多个空间频率进行采集。实验成功实现了二维光栅图像的重建,系统仿真得到的图像峰值信噪比(PSNR)为30.79 dB,实验重建图像PSNR为27.95 dB,重建图像的整体结构未发生改变。成像系统的设计及成像的过程也为该技术的实际工程应用提供了指导和方向。

一种大孔径静态干涉高光谱成像数据压缩方法

大孔径静态干涉成像遥感数据的数据量较大,需要寻找一种合适的方法对其压缩。从大孔径静态干涉成像机理出发,分析了干涉数据的空间和干涉维冗余性,并基于现有成熟混合压缩编码方法,提出了基于相似干涉曲线与不同光程差之间冗余去除的算法,对冗余数据进行去除预处理。对干涉数据进行基于曲线表的干涉曲线编码表示,对不同光程差之间的图像进行相关性预测,减少了大孔径静态干涉成像遥感图像的量化深度并降低了图像的信息熵,再结合JPEG2000算法进行无损或有损压缩。实验结果表明,对于大孔径静态干涉成像数据,该算法可实现压缩比为3.1倍的无损压缩,有损压缩的率失真曲线也优于其他对比算法,其复原图像反演出的光谱曲线的光谱角和相对二次误差均优于其他对比算法处理的数据,有效保护了光谱信息。

基于干涉条纹成像的测角系统设计及其离轴测量精度

基于干涉条纹成像的测角系统测量精度随着测量范围的增大而下降,单纯提高精定位的细分倍数并不能提高测量精度。针对这一问题,本文围绕非成像系统的参数设计方法及大测量范围下的精度变化情况展开研究。建立了双光栅干涉系统及光楔阵列波前分割的数学模型,给出了近轴条件下非成像光学系统的参数设计方法。设计了一台一维高精度光学测角系统,并对该系统在整个测角范围内的测量误差进行了分析和计算。结果显示:利用本文提出的数学模型和方法,所设计的测角系统在[-5°,5°]的测量范围内,近轴区的测角分辨率为0.02″。随着测量范围的增大,干涉条纹相位非线性变化引起的精定位误差成为系统测角误差的主要来源,最大测量角度下精密轴的测量误差为0.42″。上述结果表明采用本文提出的模型和参数设计方法,可以设计出具有较高测角精度的光学测角系统。

基于地形辅助的无人机载InSAR图像分区配准方法

小型化、轻量化的无人机(UAV)为合成孔径雷达(SAR)提供了更加灵活、机动的观测平台,无人机载干涉SAR(InSAR)逐步应用于干涉测量领域。无人机小而轻,易受气流扰动的影响,采用多航过模式进行干涉测量时,飞行航迹非线性且不平行。非线性、不平行的飞行轨迹导致两幅图像之间存在几何畸变。在复杂地形条件下,无人机载InSAR的干涉图像对之间的偏移量大且具有明显的空变特性,给图像配准带来了很大的技术挑战,常规的基于多项式拟合的配准方法不再适用。该文提出了一种利用地形辅助分区的图像配准方法。首先基于航迹信息生成高程门限,利用外部地形对测量区域进行图像分区处理,然后对区域内的偏移量构建多项式变换模型,对各区域边界处的偏移量施加约束,并进行联合求解,最后获得连续的全局偏移量拟合面,通过对辅图像进行重采样实现精配准。基于P波段无人机载InSAR获取的实测数据,初步验证了该方法的有效性。

An estimation method for InSAR interferometric phase combined with image auto-coregistration

In this paper we propose a method to estimate the InSAR interferometric phase of the steep terrain based on the terrain model of local plane by using the joint subspace projection technique proposed in our previous paper. The method takes advantage of the coherence information of neighboring pixel pairs to auto-coregister the SAR images and employs the projection of the joint signal subspace onto the corresponding joint noise subspace to estimate the terrain interferometric phase. The method can auto-coregister the SAR images and reduce the interferometric phase noise simultaneously. Theoretical analysis and computer simulation results show that the method can provide accurate estimate of the interferometric phase （interferogram） of very steep terrain even if the coregistration error reaches one pixel. The effectiveness of the method is verified via simulated data and real data.

基于星表的射电干涉阵成像评价指标研究

为了满足新一代射电干涉阵望远镜对成像结果进行质量评价的迫切需求,文章以仿真数据为基础,通过比较在成像结果上进行源搜寻得到的星表与仿真时所使用的已知参考星表之间的差异,展开对射电干涉阵成像质量评价指标的研究。不同于常用的将两个星表进行交叉匹配并比较匹配源的诸如位置、流量密度等属性的精度,文章提出了使用度量两个元素集或者分布之间差异的推土距离(Earth Mover's Distance,EMD)来量化两个星表之间的差异,以更鲁棒的数值指标评价成像质量,为进一步研究更加鲁棒的射电干涉阵成像评价指标提供了有益的参考,也有助于射电干涉阵望远镜最终获得更高质量的科学数据。