首页> 外文OA文献 >Phase error estimation for synthetic aperture imagery.
【2h】

Phase error estimation for synthetic aperture imagery.

机译:合成孔径图像的相位误差估计。

代理获取
本网站仅为用户提供外文OA文献查询和代理获取服务,本网站没有原文。下单后我们将采用程序或人工为您竭诚获取高质量的原文,但由于OA文献来源多样且变更频繁,仍可能出现获取不到、文献不完整或与标题不符等情况,如果获取不到我们将提供退款服务。请知悉。

摘要

The estimation of phase errors in synthetic aperture imagery is important for high quality images. Many methods of autofocus, or the estimation of phase errors from the measured data, are developed using certain assumptions about the imaged scene. This thesis develops improved methods of phase estimation which make full use of the information in the recorded signal. This results in both a more accurate estimate of the image phase error and improved imagery compared to using standard techniques. The standard phase estimation kernel used in echo-correlation techniques is shear-average. This technique averages the phase-difference between each ping over all range-bins, weighted by the signal strength. It is shown in this thesis that this is not the optimal method of weighting each phase estimate. In images where the signal to clutter ratio (SCR) is not proportional to the signal amplitude, shear-average does not meet the predicted error bound. This condition may be met by many image types, including those with shadows, distributed targets and varying surface structure. By measuring the average coherence between echos at each range-bin, it is possible to accurately estimate the variance of each phase estimate, and weight accordingly. A weighted phase-difference estimation (WPDE) using this coherence weighting meets the performance bound for all images tested. Thus an improved performance over shear-average is shown for many image types. The WPDE phase estimation method can be used within the framework of many echo-correlation techniques, such as phase-gradient autofocus (PGA), phase curvature estimation, redundant phase-centre or displaced phase-centre algorithms. In addition, a direct centre-shifting method is developed which reduces bias compared to the centre-shifting method used in PGA. For stripmap images, a weighted phase curvature estimator shows better performance than amplitude weighted shear-average for images with high SCR. A different method of phase estimation, known as sharpness maximisation, perturbs an estimate of the phase error to maximise the sharpness of the reconstructed image. Several improvements are made to the technique of sharpness maximisation. These include the reduction of over-sharpening using regularisation and an improvement in accuracy of the phase estimate using range-weighting based on the coherence measure. A cascaded parametric optimisation method is developed which converges significantly faster than standard optimisation methods for stripmap images. A number of novel insights into the method of sharpness maximisation are presented. A derivation of the phase that gives maximum intensity squared sharpness is extended from a noncoherent imaging system to a coherent spotlight system. A bound on the performance of sharpness-maximisation is presented. A method is developed which allows the direct calculation of the result of a sharpness maximisation for a single ping of a spotlight synthetic aperture image. The phase correction that maximises sharpness can be directly calculated from the signal in a manner similar to a high-order echo-correlation. This calculation can be made for all pings in a recursive manner. No optimisation is required, resulting in a significantly faster phase estimation. The techniques of sharpness maximisation and echo-correlation can be shown to be closely related. This is confirmed by direct comparisons of the results. However, the classical intensity-squared sharpness measure gives poorer results than WPDE and different sharpness measures tested for a distributed target. The standard methods of shear average and maximisation of the intensity-squared sharpness measure, both perform well below the theoretical performance bound. Two of the techniques developed, WPDE and direct entropy minimisation perform at the bound, showing improved performance over standard techniques. The contributions of this thesis add considerably to the body of knowledge on the technique of sharpness maximisation. This allows an improvement in the accuracy of some phase estimation methods, as well as an increase in the understanding of how these techniques work on coherent imagery in general.
机译:合成孔径图像中相位误差的估计对于高质量图像很重要。使用关于成像场景的某些假设,开发了许多自动聚焦方法或根据测量数据估算相位误差的方法。本文提出了一种改进的相位估计方法,该方法充分利用了记录信号中的信息。与使用标准技术相比,这既可以更准确地估计图像相位误差,又可以改善图像质量。回波相关技术中使用的标准相位估计核心是剪切平均。这项技术将平均范围内所有ping之间每个ping之间的相位差平均化,并通过信号强度进行加权。本文证明,这不是加权每个相位估计的最佳方法。在信噪比(SCR)与信号幅度不成比例的图像中,剪切平均值不符合预测的误差范围。许多图像类型都可以满足此条件,包括阴影,分布目标和表面结构变化的图像类型。通过测量每个范围区间回波之间的平均相干性,可以准确估计每个相位估计的方差,并相应地加权。使用此相干加权的加权相位差估计(WPDE)满足了所有测试图像的性能要求。因此,对于许多图像类型,均显示了优于剪切平均的性能。 WPDE相位估计方法可以在许多回波相关技术的框架内使用,例如相位梯度自动聚焦(PGA),相位曲率估计,冗余相位中心或位移相位中心算法。另外,开发了一种直接的中心偏移方法,与PGA中使用的中心偏移方法相比,该方法可减少偏差。对于带状图图像,对于具有高SCR的图像,加权幅度曲率估计器的性能优于幅度加权剪切平均。一种不同的相位估计方法(称为锐度最大化)会扰乱相位误差的估计,以使重建图像的锐度最大化。锐度最大化技术进行了几项改进。这些措施包括使用正则化减少过度锐化,以及使用基于相干性度量的范围加权来提高相位估计的准确性。开发了一种级联参数优化方法,该方法的收敛速度比带状图图像的标准优化方法快得多。提出了许多关于锐度最大化方法的新颖见解。给出最大强度平方锐度的相位求导从非相干成像系统扩展到相干聚光灯系统。提出了清晰度最大化性能的界限。开发了一种方法,该方法可以直接计算一次聚光灯合成孔径图像的清晰度最大化的结果。可以以类似于高阶回波相关的方式直接从信号中计算出使锐度最大化的相位校正。可以以递归方式对所有ping进行此计算。无需优化,可大大加快相位估计。锐度最大化和回声相关技术可以证明是密切相关的。通过直接比较结果可以确认这一点。但是,经典的强度平方锐度度量比WPDE的结果差,并且针对分布式目标测试了不同的锐度度量。剪切平均值的平均方法和强度平方锐度度量的最大化方法都在理论性能范围以下进行。所开发的两项技术WPDE和直接熵最小化在边界上表现出色,显示出比标准技术更高的性能。本论文的贡献极大地增加了锐度最大化技术的知识体系。这可以提高某些相位估计方法的准确性,并且可以增加对这些技术通常如何在相干图像上工作的理解。

著录项

  • 作者

    Fortune Steven A.;

  • 作者单位
  • 年度 2005
  • 总页数
  • 原文格式 PDF
  • 正文语种 en
  • 中图分类

相似文献

  • 外文文献
  • 中文文献
  • 专利

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号