共查询到16条相似文献,搜索用时 390 毫秒
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在ISAR成像中,目标的非均匀转动会引入与散射点位置有关相位误差,无法用统一的相位误差函数表示,因此通常的自聚焦方法难以消除。针对加速转动目标,本文提出了一种基于离散调频傅立叶变换(discrete chirp-Fourier trans- form)的自聚焦算法。在预先选定的距离单元上,利用离散调频傅立叶变换提取最大功率散射点对应的调频信号,并以之为参考信号消除目标平动引起的相位误差。然后,利用同样的方法,在多个距离单元上提取最大功率散射点对应的调频信号,根据该散射点信号估计目标非均匀转动的参数,并进行非均匀采样,去除非均匀转动的相位误差。将该算法应用于仿真试验和实测数据的ISAR成像中,都得到了较好的聚焦结果。 相似文献
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在对复杂运动目标进行逆合成孔径雷达成像时,由于转动矢量随时间而变化,回波信号中会引入一个与散射点位置有关的相位误差,无法用通常的相位补偿方法进行校正,应用距离-多普勒算法获得的ISAR(Inverse Synthetic Aperture Radar)像会变得模糊.本文分析了目标转动矢量变化使得ISAR像模糊的内在原因,给出了目标三维转动状态下的ISAR信号形式,并基于散射点信号的特点提出了一种复杂运动目标的ISAR成像算法.该算法不仅适用于转动矢量方向不变的非均匀转动目标,而且对于转动矢量方向缓慢变化的目标,算法仍然能够有效地提高ISAR成像的质量.仿真试验结果表明了该算法的有效性. 相似文献
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在ISAR成像中,目标的非均匀转动会引入与散射点位置有关的相位误差,无法用统一的相位误差函数表示,而散射点子回波的相位精度对于ISAR自聚焦的相位校正非常重要.针对加速转动的目标,提出了一种基于分数阶傅里叶变换(FRFT:fractional Fourier transform)的自聚焦算法.在预先选定的距离单元上,利用分数阶傅里叶变换提取最大功率散射点对应的调频信号,并以该信号为参考信号消除目标平动引起的相位误差.利用同样的方法,在多个距离单元上提取最强散射点对应的调频信号,并对调频信号的估计值加权平均,得到非均匀转动参数的最优估计,进而对信号非均匀采样,消除非均匀转动的相位误差.仿真结果验证了该算法能够很好地消除相位误差. 相似文献
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在ISAR成像中,由非均匀转动引起的相位误差与散射点的径向位置有关,传统的相位聚焦方法难以采用统一的相位校正函数来进行补偿。针对此问题,提出一种基于自适应Gaussian包络Chirplet分解(AGCD)快速算法的相位补偿方法。该方法在任意选取的距离单元上,利用Gaussian包络Chirplet分解得到两个较强散射点所对应的线性调频信号参数,并结合多特显点处理(PPP)模型,对由平动和非均匀转动造成的相位误差分别进行补偿。该方法计算量小,估计精度高,且没有孤立强散射点的要求。仿真实验结果表明了它的有效性。 相似文献
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针对方位向稀疏采样条件下,大带宽大转角ISAR高分辨成像时,转动分量引起的一维距离像中目标散射点的距离走动和空变二次相位问题,研究了一种稀疏采样数据ISAR高分辨成像方法。对于方位向稀疏采样数据,该方法在包络对齐和相位补偿后,将Keystone变换和稀疏恢复相结合,实现方位向稀疏采样数据距离走动校正和缺失采样位置一维像重建,接着采用基于LVD变换的二阶相位估计方法对二阶转动相位进行估计并补偿,完成高分辨成像。计算机仿真和暗室测量数据验证了该方法的有效性。 相似文献
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Yao Wei Xinggan Zhang Yechao Bai Lan Tang 《Multidimensional Systems and Signal Processing》2014,25(4):759-773
In inverse synthetic aperture radar (ISAR) imaging, translation compensation should be done before range-Doppler imaging process, and range alignment is the first step for translation compensation. In order to remove the limitation of integer range bin and align the echoes precisely for ISAR range alignment, combining with the advantage of array signal processing at fractional unit delay compensation, we propose a novel range alignment method based on linear transmitting/receiving (T/R) array. Firstly the ISAR imaging system is modeled as a linear T/R array. Then based on the snapshot imaging model of linear T/R array, range alignment is accomplished by wave path difference compensation which is transformed into the phase difference compensation in frequency domain between adjacent array elements. The phase difference compensation consists of integer range bin alignment and decimal time delay compensation which is implemented by the phase rotation’s estimation and compensation in frequency domain. Finally, the results of simulation data and real radar data are provided to demonstrate the effectiveness of the proposed method. 相似文献
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This paper first studies the phase errors for fine-resolution spotlight mode SAR imaging and decomposes the phase errors into two kinds, one is caused by translation and the other by rotation.Mathematical analysis and computer simulations show the sbove mentioned motion kinds and their corresponding damages on spotlight mode SAR imaging.Based on this analysis, a single PPP is introduced for spotlight mode SAR imaging with the PFA on the assumption that relative rotation between APC and imaged sceme is uniform.The selected single point is used first to correct the quadratic and higher order phase errors and then to adjust the linear errors.After this compensation, the space-invariant phase errors caused by translation are almost corrected.Finally results are presented with the simulated data. 相似文献
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Sekihara K 《IEEE transactions on medical imaging》1987,6(2):157-164
The steady-state magnetizations in three versions of rapid NMR imaging using small flip angles and short repetition intervals are studied. It is shown that in the original version, the estimation using (1 - E(1)) sin alpha/(1 - E(1) cos alpha) contains errors that depend on the increment of the phase rotation angle arising from the phase encoding process. The modified version of rapid imaging, where the phase rotation due to the phase encoding process is compensated for in each time interval, can have sensitivity superior to the original version where the phase rotation is not compensated for. Here, flip angles larger than the Ernst angle must be used. In the third version, the steady-state magnetization is obtained by a rapid imaging sequence in which the phase rotations arising not only from the application of the phase encoding gradient but also from the applications of other gradients are compensated for. Analysis of this version showed a remarkable increase in sensitivity although it required the use of an extremely uniform field. It is estimated that this increase reaches 80 percent with a repetition interval of 10 ms, although a field uniformity less than 1 muT is necessary. 相似文献
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一种估计ISAR成像转角的新方法 总被引:1,自引:0,他引:1
ISAR成像中的转角估计是进行正确成像的先决条件。该文从分析目标回波信号入手提出了一种新的转角估计方法,对目标转动时不同距离单元回波数据近似为多分量三次相位信号,通过理论推导,得出每个信号分量的三次相位系数与一次相位系数成正比的结论,其比例系数为目标转动的角速度平方,然后采用最大似然方法估计三次相位信号参数,进而得到总转角。外场实测数据结果验证了该文方法的有效性。 相似文献
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大距离徙动情况下距离多普勒(RD)算法与后向投影(BP)算法的比较 总被引:1,自引:1,他引:0
距离多普勒(Range-Doppler,RD)算法是传统窄带/窄波束SAR的经典成像算法,它借助菲涅耳近似,只保留了斜距R(t)的线性部分和二次项。但是当距离徙动严重时,方位向二次以上的高次相位项不能忽略,这会大大降低聚焦精度。后向投影(Back-Projection,BP)算法是一种基于时域处理的成像算法,通过计算双程延时将对应信号进行相干累加,获得高分辨率SAR图像。BP算法由于用时延代替了相位的概念,故与频率无关,不存在距离徙动校正的问题。本文介绍了RD算法和BP算法的原理及算法实现,并且利用距离向插值改进了BP算法。最后,结合计算机仿真结果详细比较了这两种算法的若干性能指标,证明了BP算法比RD算法更适用于大距离徙动情况下的SAR成像。 相似文献