A new coherent integration method for weak maneuvering target with jerk motion

In radar systems, prolonging the integration time helps to improve the detection and estimation performance of weak target. However, in a long integration time, target's high-order motion is non-ignorable, which causes high-order range migration (RM) and Doppler frequency migration (DFM) problems. The RM and DFM defocus the integration result and lead to detection and estimation performance loss. In this paper, a new coherent integration method is proposed for maneuvering radar target with jerk motion. First, we define a new cross correlation function basing on non-uniformly resampling technique. By using this function, we eliminate the range migration (RM) and Doppler frequency migration (DFM) caused by target's velocity and acceleration. Then, matched filtering process is performed to compensate the phase error caused by target's jerk motion. Finally, the integration is achieved by summing signal data in different range frequency cells and performing a two-dimensional fast Fourier transform (FFT). The proposed method is applicable for low signal-to-noise ratio (SNR) environment. Compared with the GRFT algorithm, the proposed method has a close integration performance and a lower computational complexity. The effectiveness is validated by simulations and real-data processing results.     

时间相位解包裹算法仿真与实验研究

为提高基于编码光栅的物体三维轮廓重构的精度,消除多频时间相位解包裹算法的相位跳跃性误差。采用一种改进的三频相位解包裹算法,通过相位与光栅节距的关系,实现了精准的相位解包裹。相比于传统方法和已提出的方法,提出的方法解相精度更高。通过仿真分析可得,改进方法展开相位无跳跃性误差,无需相位矫正,且在外加较大干扰的情况下也不会产生2π周期性误差,减小了相位解包裹的非线性误差。通过实验分析可得该方法实现了较高精度的物体三维轮廓重构。     

基于GLONASS的双基合成孔径雷达的预处理算法研究

本文提出了一种基于GLONASS的双基合成孔径雷达(GLONASS based Bistatic Synthetic Aperture Radar, GLONASS-BSAR)的预处理算法。GLONASS-BSAR雷达系统采用俄罗斯导航卫星GLONASS作为发射机,接收机可以放置在任意平台,比如卫星、飞机、汽车或者地面。该系统有着低廉的成本、较好的安全性以及多视角等技术优势,应用前景广阔。然而,由于该系统属于非合作式双基地雷达系统,发射机与接收机时间、频率以及相位上不同步,对雷达处理引入了严重的技术限制。才外,该雷达系统的发射机卫星属于中高轨道卫星,因此接收信号信噪比极低,大大增加了后续信号处理的难度。因此,本文拟研究GLONASS-BSAR的预处理算法,获取该雷达系统的同步。该预处理算法通过对接收到的信号进行时间延时、频率、相位历史信息提取,能够消除双基合成孔径雷达系统带来的时间不同步以及相位不同步。实验结果表明,该预处理算法能够消除接收信号的时间不同步和相位不同步,同时运算复杂度低。     

An extended PUMA algorithm for multibaseline InSAR DEM reconstruction

Phase unwrapping (PU) is one of the key processes in reconstructing the digital elevation model (DEM) of a scene from its corresponding interferometric synthetic aperture radar (InSAR) data. In contrast to traditional single-baseline PU, the multibaseline PU does not require phase continuity, which is useful when reconstructing the DEM in cases where the topography varies sharply. However, the performance of the multibaseline PU is directly related to the noise level, whereas the single-baseline PU algorithm has favourable noise robustness since it is based on the global wrapped phase information, e.g. the PU-max-flow (PUMA) algorithm. To improve the noise robustness of the multibaseline unwrapping process, we extend the single-baseline PUMA algorithm in this paper to a multibaseline domain, referred to as the multibaseline PUMA algorithm, which allows the unwrapping of multibaseline interferograms to generate the DEM. The proposed algorithm is less influenced by the phase continuity assumption by taking advantage of the multibaseline diversity and improves the noise robustness by using the global wrapped information from both single- and multibaseline domains. The performance of the proposed algorithm is tested on both simulated and real InSAR data experiments to demonstrate the effectiveness and noise robustness of the proposed algorithm.     

Optimal estimation of interferometric phase for measuring surface deformation

In recent times, time-series interferometric synthetic aperture radar (InSAR) methods are developed to retrieve the deformation signal in non-urban areas from distributed scatterers (DS). Phase triangulation algorithm (PTA), an important step in these methods for filtering decorrelation noise from DS, aims at optimal estimation of the filtered wrapped interferometric phase values using InSAR data stack. The uniqueness of this research work lies in the incorporation of one such PTA only to provide an optimal set of wrapped interferometric phase values before phase unwrapping in the open source StaMPS processing environment. The proposed methodology, when adapted to measure surface deformation in Tehri reservoir rim region, Uttarakhand, India using Environmental Satellite (Envisat) C-band advanced synthetic aperture radar images, works efficiently and has enhanced the spatial coverage of measurement pixels compared to standalone PS-InSAR processing. It is also revealed from the one-dimension-line of sight velocity map that resulted velocity estimates are congruent with standalone PS-InSAR processing.     

基于掩膜的加权卡尔曼滤波相位解缠算法

卡尔曼滤波将相位解缠转化为状态估计问题,同时实现相位解缠与噪声消除。由于原始雷达信号以及后处理过程中产生的诸多误差,造成相位数据不连续产生局部误差传递,使得解缠结果不准确。提出一种基于掩膜的加权卡尔曼滤波相位解缠算法。该算法通过对包缠数据中的低质量区域进行掩膜处理,对掩膜后的高质量区域进行卡尔曼滤波相位解缠,再对掩膜区域实施加权卡尔曼滤波相位解缠,得到了较为可靠的相位解缠结果。采用仿真数据和ALOS卫星的山东兖矿地区干涉SAR数据进行实验,验证了算法的有效性和可靠性。     

相位解包裹技术及应用研究进展

相位解包裹技术是光学相位测量中获得连续相位分布的一项关键技术,解包结果的好坏直接影响测量结果的精度高低。近年来该技术广泛应用于散斑干涉测量、合成孔径雷达等领域。从两大类相位解包裹技术出发,详细论述了各类路径跟踪解包裹算法和最小范数解包裹算法的实现方式,并分析比较各算法的优缺点;最后介绍了相位解包裹的国内外发展与应用,展望了相位解包裹技术在抗噪能力、解包裹效率以及解包裹结果定量评价等方面的发展趋势。     

一种适应于IEEE 802.15.4k标准的高精度频偏估计算法

为实现基于IEEE 802.15.4k标准的长码字直接序列扩频系统(Direct sequency spread spectrum, DSSS)在低信噪比下的频偏估计,提出一种高精度、稳定的改进频偏估计算法。该算法在保证频偏估计范围的前提下同时利用相位和幅度信息对信号作有偏自相关和迭代,提高包含相位信息的序列的信噪比,然后对有偏自相关信号的各阶差分计算相位幅角并加权平均,克服了 Fitz方法在低信噪比下近似条件难以满足的缺点。实验结果表明该算法能在不缩小估计范围的同时实现极低信噪比下的精确频偏估计,估计精度满足IEEE 802.15.4k标准下接收系统对残余频偏的容忍度。     

一种提高雷达作用距离的有效方法

雷达的作用距离与雷达对目标的最低可检测信噪比直接相关,现代雷达要达到对目标的可靠检测,一般要求单个脉冲的信噪比为13dB左右．为此,将低门限检测、卡尔曼滤波与动态规划算法相结合,以在雷达中实现检测前跟踪,并给出了检测前跟踪与检测后跟踪相衔接的方法．该方法使雷达将可靠检测的信噪比降到7dB左右,相当于将雷达的最大作用距离提高了近40％．仿真结果表明,所提出的方法是可行而有效的。     

Vertical structure and evolution of a supercell storm: observations using VHF radar

An attempt has been made in the present study to characterise the vertical kinematic structure of a supercell storm during its different phases of development. The present study utilises the high time and height resolution 53 MHz VHF radar observations at Gadanki (13.5° N, 79.2° E), India. A supercell storm passed over the radar site during 17–18 October, 2002, and has been sampled during its mature to dissipating stages of convective activity. The time height variation of the radar reflectivity in terms of signal to noise ratio (SNR) and spectral width along with vertical velocity have been used to separate two distinct phases of the convective activity associated with the supercell storm. The mature phase of the storm is characterised by enhancement of high value of SNR from the lower troposphere up to the height of the tropopause. During this period, the vertical velocity in the middle troposphere is of the order of 8 to 10 ms^?1. The dissipating stage is characterised by diminished structure of SNR in the middle and upper troposphere. During this period, downwards motion is present in the troposphere. Oscillatory nature of the vertical velocity is found in the upper tropospheric/lower stratospheric (UT/LS) region and shows signatures of short period gravity waves. The power spectral and wavelet analysis of the vertical wind perturbations shows signatures of high frequency oscillations of periodicity between 8–30 min. These high frequency waves are possibly owing to the oscillating updrafts and downdrafts impinging on the tropopause owing to penetrative convection.     

一种目标速度精确测量的新方法

提出了一种CW雷达目标速度测量的新方法,该方法运用离散多项相位变换法先获得目标加速度,然后利用该值对雷达回波进行加速度补偿并基于FFT和插值FFT获得速度值。又考虑到经过雷达信号处理机后得到的速度值存在波动和野值,运用自适应卡尔曼滤波进行处理,剔除野值。相比于传统的测速方法,该方法提高了测量精度,同时也较好地消除了雷达系统噪声,提高了测速系统的稳定性。计算机仿真和外场实测数据处理结果表明了该方法的有效性。     

一种利用叠加降噪提高二次相关TDOA精度的方法

二次相关TDOA算法具有一定的抗噪声性能,但在信噪比很低的条件下无法准确估计出时延。针对二次相关TDOA算法,在低信噪比下可能存在误差的情况,提出了利用叠加降噪提高接收信号的信噪比的新方法,从而提高算法精度。在接收到信号后,算法依据统计学的理论,采用信号叠加降噪的方法提高信号的信噪比,从而提升二次相关TDOA结果的精度。通过仿真结果表明,在低信噪比的情况下改进后的算法在较大程度上提升了时延估计的精度,提高了二次相关TDOA的应用范围。     

Multi-mode PolInSAR experiments using an airborne X-band SAR system in China

In this paper, we describe our polarimetric interferometric synthetic aperture radar (PolInSAR) experiments with high-resolution X-band data acquired by a multi-mode airborne SAR system over an area of Linshui in southern China. First, we introduce our latest multi-mode X-band airborne imaging radar system (Multi-Mode-XSAR), which integrates three operation modes of bistatic, ping-pong, and mixed. Then, the Multi-Mode-XSAR data set and the corresponding ground measurements in test areas are briefly described. Considering the characteristics of the Multi-Mode-XSAR imagery, a dual-baseline polarimetric interferometry (DPI) method is proposed in this article. The proposed method guarantees a high coherence on the full polarimetric data and combines the benefits of short and long baselines to facilitate the phase unwrapping and promote height sensitivity. Our PolInSAR experiment results demonstrate that the DPI method is capable of generating DSM with higher accuracy than other multi-baseline (MB) methods and the Multi-Mode-XSAR imagery has great potential in PolInSAR applications.     

一种相位编码算法在气象雷达中的应用

描述一种被称为SZ相位编码的解距离模糊方法在脉冲多普勒气象雷达中的应用．首先给出了该方法应用到某气象雷达上所采用的系统框图；然后介绍了SZ相位编码的原理和编码序列以及基于这种编码给出了气象雷达解距离模糊算法的详细流程，并着重介绍了频谱重构的频域处理方法；最后给出了用该方法同时解出一次和二次气象回波的Matlab仿真，结果表明该方法对平均速度的估算较为准确．     

高斯噪声下伪码-线性调频复合信号参数提取方法

针对目前雷达信号参数估计算法在某种环境中性能急剧下降,甚至失效的问题,提出一种基于多相滤波器组和高阶累积量联合处理的伪码-线性调频复合信号参数估计算法.该算法首先利用多相滤波器组实现信号在频域上快速均匀划分,然后对输出的每个子带信号进行三阶累积量对角切片的短时估计,有效抑制高斯噪声的干扰,并经过包络检波后得到复合信号完整的时频矩阵,最后通过时频图像的Radon变换和频率曲线的提取实现信号伪码数目、码元宽度、调频斜率、信号载频、带宽以及起止频率的提取.仿真结果表明,该方法在信噪比大于-11 dB时的估计精度较高.     

Phase unwrapping method based on image segmentation

In this Letter, a method is proposed for interferometric synthetic aperture radar (SAR) phase unwrapping based on image segmentation. An auxiliary phase map was generated and the interferometric phase was divided into many connected regions without discontinuity by separation and combination operations. A local optimal strategy was used to combine these regions with as few discontinuities as possible. The coherence map is not necessary. The authors compared the proposed method with Goldstein's branch‐cut algorithm (BC) and the weighted multi‐grid algorithm (WMG), demonstrating the effectiveness of the proposed method.     

A new phase unwrapping method based on region recognition and region expansion

Phase unwrapping is a key step in retrieving digital elevation models (DEMs) from across-track interferometric synthetic aperture radar (InSAR) data. The coherence of synthetic aperture radar (SAR) data set is an effective indicator for the quality of phase unwrapping. However, the coherence of different regions usually distributes unevenly in SAR images monitoring heterogeneous areas. Errors in low-coherence areas are prone to pollute the whole image. In order to mitigate propagation error, a new phase unwrapping algorithm based on region recognition and region expansion is proposed. In the region recognition step, optical images are incorporated to recognize low-coherence regions by virtue of supervised classification technique. Low-coherence regions and the ones that are not of interest for the application are then discarded. In the region expansion step, stable pixels of high coherence are selected as growing seeds, and then phase unwrapping grows from high-quality regions to low-quality ones guided by coherence information and weighted numbers of neighbouring unwrapped pixels. The ambiguity number of a wrapped pixel is estimated from its neighbouring pixels under the criteria of pixel distance and phase gradient. Iterative examination continues until the whole image is unwrapped. Experiments on PALSAR and ASAR data demonstrate its validity and advantages over other classical methods.     

Coherent integration loss due to pulses loss and phase modulation in passive bistatic radar

The purpose of this paper is to analyze the amplitude and phase modulation effect incurred by the rotating transmit antenna in passive bistatic radar, which result in pulses loss and phase reversals within the direct-path pulse train. The processing loss mechanisms of signal to noise ratio (SNR) and offsets in target Doppler measurements caused by the pulses loss and phase reversals are described. The expressions of the peak output of cross-ambiguity function are derived to evaluate SNR loss in the presence of pulses loss or/and phase reversals. Simulation results show that the maximum SNR loss is about 3.5 dB, and the SNR loss curves for various Doppler frequencies and different number of lost pulses are conformed to the theoretical analysis. The SNR loss gets progressively worse with increasing target Doppler frequency. The frequency estimation error increases with target Doppler frequency and lost pulse number, up to a worst case of about 0.75 of a Doppler cell.     

优化的区域增长InSAR相位解缠算法

在区域增长的干涉合成孔径雷达（InSAR）相位解缠算法中,种子的选择和种子相位值的确定是之一.本文研究了优化的区域增长2维相位解缠方法,包括合适的种子选取和种子相位值的优化处理,提出了将干涉相位图中相位跳变导致的边缘曲线作为种子,通过分析边缘曲线之间的相邻关系,基于遗传算法优化种子的相位值.仿真结果表明,该算法的计算量与干涉相位图的像素点数成近似线性关系,同时由于该算法属于局部算法,可以通过并行处理进一步提高计算效率.优化的区域增长2维相位解缠算法与其他2维相位解缠算法相比较,其解缠后的相位条纹与原始干涉相位图相位条纹的一致性非常好.该算法的处理结果与最小成本网络流相位解缠法相当,但其计算量却远远小于最小成本网络流相位解缠法的计算量.     

A multilevel graph algorithm for two dimensional phase unwrapping

Two-dimensional phase unwrapping is the problem of deducing unambiguous “phase” from values known only modulo 2π. Many authors agree that the objective of phase unwrapping should be to find a weighted minimum of the number of places where adjacent (discrete) phase values differ by more than π (called discontinuities). This NP-hard problem is of considerable practical interest, largely due to its importance in interpreting data acquired with synthetic aperture radar (SAR) interferometry. Consequently, many heuristic algorithms have been proposed. We present an efficient multi-level graph algorithm for the approximate solution of an equivalent problem—minimal residue cut in the dual graph.