共查询到18条相似文献,搜索用时 203 毫秒
1.
提出了一种星载合成孔径雷达数字成像抑制相干斑的算法--OMRD(Overlapped Multilook Range-Doppler)算法,该算法基于星载合成孔径雷达成像基本原理和传统的RD算法,通过距离向脉冲压缩,距离徙动校正,方位向合成孔径处理,去除相干斑噪声处理,实现了星载合成孔径雷达的数字成像,降低了相干斑噪声的影响,提高了图像信噪比.对ERS-1星载原始数据进行实验成像,得到了清晰的意大利罗马地区图像.实验结果表明,OMRD算法是一种有效的星载合成孔径雷达成像抑制相干斑的算法. 相似文献
2.
平飞斜视模式双站合成孔径雷达数据处理算法 总被引:1,自引:0,他引:1
研究了发射和接收分离的双站合成孔径雷达成像算法.主要分析了双站合成孔径雷达在平飞斜视工作模式下的方位分辨率,以及二次距离徙动校正判据,研究了利用非线性Chirp Scaling(NLCS)的方法,来消除同一距离单元上的不同方位调频斜率带来的影响,并且推导出了平飞斜视模式下的方位匹配滤波函数的频域表示,通过点目标成像仿真验证了该方法的正确性. 相似文献
3.
4.
基于两步处理算法和ChirpScaling算法,提出一种适用于条带式成像算法的通用高分辨聚束式合成孔径声呐(SAS)模型。该模型结合了谱分析(SPECAN)算法和ChirpScaling算法的优点,算法首先采用deramp和升采样处理技术实现方位的粗聚焦,消除了聚束式SAS特有的方位频谱混迭现象,然后应用ChirpScaling原理实现距离的精确聚焦,并补偿deramp处理引起的方位相位误差,实现方位精聚焦。基于该通用模型,给出了实现的步骤,整个算法无需任何插值操作,只需复乘和FFT即可完成。该算法适用于宽测绘带高分辨率聚束式SAS的精确而高效成像处理。最后,通过计算机仿真,验证了该通用模型的有效性。 相似文献
5.
编队目标由于各目标回波在距离域和多普勒域都有重叠,难以直接利用单目标的成像方法对多目标进行成像。本文提出先对多目标进行统一的距离走动校正,然后采用广义二阶keystone变换校正距离弯曲,最后采用基于调幅-线性调频信号模型的参数估计方法得到多目标的距离-瞬时多普勒图像。仿真数据的处理表明了所提方法的有效性。 相似文献
6.
7.
立体视觉图像校正是加速立体匹配简单而常用的技术之一。采用几何法对使用棱镜的单镜头立体视觉系统图像进行校正,根据成像原理,从图像平面像素点反推到三维实体点的分析运算,利用成像光线几何关系求解虚拟相机外部参数,实现极线的校正,避免了复杂相机标定过程。同时,该算法可以从双棱镜应用推广到多面棱镜的单棱镜立体视觉系统图像校正。实验结果表明,基于几何法对使用棱镜的单镜头立体视觉系统图像校正是有效的。 相似文献
8.
9.
10.
11.
The traditional Range Doppler (RD) algorithm is unable to meet practical
needs owing to the limit of resolution. The order of fractional Fourier Transform (FrFT)
and the length of sampling signals affect SAR imaging performance when FrFT is
applied to RD algorithm. To overcome the above shortcomings, the purpose of this paper
is to propose a high-resolution SAR image algorithm by using the optimal order of FrFT
and the sample length constraints for the range direction. The expression of the optimal
order of SAR range signals via FrFT is deduced in detail. The initial sample length and
its constraints are proposed to obtain the best sample length of SAR range signals.
Experimental results demonstrate that, when the range sampling-length changes in a
certain interval, the best sampling-length will be obtained, which the best values of the
range resolution, PSLR and ISLR, will be derived respectively. Compared with
traditional RD algorithm, the main-lobe width of the peak-point target of the proposed
algorithm is narrow in the range direction. While the peak amplitude of the first side-lobe
is reduced significantly, those of other side-lobes also drop in various degrees. 相似文献
12.
为解决纠偏传输时纸塑复合袋易产生褶皱的问题,设计了一种磁力压紧纠偏装置。首先,综合利用磁压紧皮带、传送带和磁铁位置调整装置等零部件,完成了纸塑复合袋磁力压紧纠偏装置的结构设计,并根据纸塑复合袋的受力分析,建立了动态磁力压紧纠偏数学模型。然后,对纸塑复合袋磁力压紧纠偏装置进行有限元建模,并根据纸塑复合袋纠偏过程设置边界条件及接触参数,采用显示动力学分析方法对其动态纠偏过程进行仿真。接着,基于仿真结果,结合BP(back propagation,反向传播)神经网络和GA(genetic algorithm,遗传算法)(简称为BP-GA算法),建立了纸塑复合袋磁力压紧纠偏装置工艺参数优化模型。最后,通过相应的计算程序,实现了纸塑复合袋磁力压紧纠偏装置工艺参数的优化。结果表明:所设计的纸塑复合袋磁力压紧纠偏装置能较好地实现纠偏功能,可使纸塑复合袋在传输时产生的褶皱符合设计要求;纠偏时该装置的最优工艺参数为电磁铁磁力为7 N,左、右两侧皮带组件的间隙为476 mm,皮带组件与纸塑复合袋之间的动摩擦系数为0.25,实验结果与基于BP-GA算法的寻优结果较为一致。研究结果可为纸塑复合袋连续磁力纠偏的深入研究提供一定的参考。 相似文献
13.
To address the low-resolution imaging problem in relation to traditional Range
Doppler (RD) algorithm, this paper intends to propose a new algorithm based on
Fractional Fourier Transform (FrFT), which proves highly advantageous in the
acquisition of high-resolution Synthetic Aperture Radar (SAR) images. The expression of
the optimal order of SAR range signals using FrFT is deduced in detail, and the
corresponding expression of the azimuth signal is also given. Theoretical analysis shows
that, the optimal order in range (azimuth) direction, which turns out to be very unique,
depends on the known imaging parameters of SAR, therefore the engineering
practicability of FrFT-RD algorithm can be greatly improved without the need of order
iteration. The FrFT-RD algorithm is established after an analysis of the optimal timefrequency transform. Experimental results demonstrate that, compared with traditional
RD algorithm, the main-lobe width of the peak-point target of FrFT-RD algorithm is
narrow in both range and azimuth directions. While the peak amplitude of the first sidelobe is reduced significantly, those of other side-lobes also drop in various degrees. In
this way, the imaging resolution of range and azimuth can be increased considerably. 相似文献
14.
Effect of processing method on migration of antioxidant from HDPE packaging into a fatty food simulant in terms of crystallinity 下载免费PDF全文
Migration of additives from plastic packaging into food products is generally considered to be affected by polymer crystallinity. In the present work, migration of Irganox 1010 from high density polyethylene into a fatty food simulant (ethanol 95%) was studied for samples prepared with different percent crystallinities. For this purpose, 2 different processing techniques, injection and compression molding, were used, and the preparation conditions were changed to obtain high density polyethylene samples with crystallinities in the range of 50 to 70%. Migration analysis was carried out at 121°C for 2 hours, and then at 40°C for 238 hours using high performance liquid chromatography. In general, the injection molded specimens had lower crystallinity and higher overall migration than the compression molded ones. A similar trend for both injection and compression molded samples was observed indicating that the overall migration was a function of crystallinity degree. However, the specific migration rates of Irganox 1010 especially before 50 hours were found to be different for the 2 processing methods because of dissimilar morphologies. Theoretical modeling based on Fickian diffusion was applied to give more insights into the involved processes during specific migration. The interaction of the food simulant with the polymer was taken into account considering the food sorption into the polymer. By fitting the model on experimental data, it was possible to obtain the model parameters such as partition coefficients (K) and the swelling constant (B) as a function of sample crystallinity. 相似文献
15.
Hlaing S Gilerson A Harmel T Tonizzo A Weidemann A Arnone R Ahmed S 《Applied optics》2012,51(2):220-237
Water-leaving radiances, retrieved from in situ or satellite measurements, need to be corrected for the bidirectional properties of the measured light in order to standardize the data and make them comparable with each other. The current operational algorithm for the correction of bidirectional effects from the satellite ocean color data is optimized for typical oceanic waters. However, versions of bidirectional reflectance correction algorithms specifically tuned for typical coastal waters and other case 2 conditions are particularly needed to improve the overall quality of those data. In order to analyze the bidirectional reflectance distribution function (BRDF) of case 2 waters, a dataset of typical remote sensing reflectances was generated through radiative transfer simulations for a large range of viewing and illumination geometries. Based on this simulated dataset, a case 2 water focused remote sensing reflectance model is proposed to correct above-water and satellite water-leaving radiance data for bidirectional effects. The proposed model is first validated with a one year time series of in situ above-water measurements acquired by collocated multispectral and hyperspectral radiometers, which have different viewing geometries installed at the Long Island Sound Coastal Observatory (LISCO). Match-ups and intercomparisons performed on these concurrent measurements show that the proposed algorithm outperforms the algorithm currently in use at all wavelengths, with average improvement of 2.4% over the spectral range. LISCO's time series data have also been used to evaluate improvements in match-up comparisons of Moderate Resolution Imaging Spectroradiometer satellite data when the proposed BRDF correction is used in lieu of the current algorithm. It is shown that the discrepancies between coincident in-situ sea-based and satellite data decreased by 3.15% with the use of the proposed algorithm. This confirms the advantages of the proposed model over the current one, demonstrating the need for a specific case 2 water BRDF correction algorithm as well as the feasibility of enhancing performance of current and future satellite ocean color remote sensing missions for monitoring of typical coastal waters. 相似文献
16.
为克服快速分形图像编码带来的解码图像质量下降问题,提出了一种神经网络与方差混合编码的快速分形图像编码算法.该算法结合图像子块复杂度与方差值的对应关系,根据每个区块的方差值大小选择适当的映射编码方法,即对于方差值相对小的区块采用方差编码以提高编码速度,对于方差值相对大的区块采用神经网络编码以提高编码质量.该算法可以较好地修正传统分形编码中由于自仿射映射结构限制所带来的解码质量偏低的问题,在大幅提高编码速度的同时,很好地保持了图像的编码质量.实验结果表明,该算法对比基本分形编码算法可以加速24倍,解码图像的质量对比方差快速分形编码算法有1.1dB的提高.同时,该算法的硬件实现比较容易,非常贴近实用化. 相似文献
17.
Visualisation of high dynamic range images requires compression of the data to be properly displayed on media with more limited dynamic ranges. Astronomical images pose a difficult challenge for dynamic range compression algorithms, due to the nature of the imaged objects and to the lack of a reflectance illumination model based on spatial frequencies. As a result, most of the algorithms commonly used for daylight high dynamic range compression fail in achieving an optimal visualisation of astronomical targets. We propose an extended multiscale algorithm based on compression of the dynamic range in the gradient domain. Our algorithm effectively compresses the dynamic range, enhances local contrast and avoids noise amplification. This is achieved with a multiscale representation of the image and the use of luminance information. Our results show a significantly improved visualisation of astronomical images compared to the standard gradient domain compression, as well as more robustness to noise and better artefact suppression. 相似文献
18.
《成像科学杂志》2013,61(2):241-251
AbstractImage hashing is an emerging technology in multimedia security. It uses a short string called image hash to represent an input image and finds applications in image authentication, tamper detection, digital watermark, image indexing, content-based image retrieval and image copy detection. This paper presents a hashing algorithm based on the observation that block entropies are approximately linearly changed after content-preserving manipulations. This is done by converting the input image to a fixed size, dividing the normalised image into non-overlapping blocks, extracting entropies of image blocks and applying a single-level 2D discrete wavelet transform to perform feature compression. Correlation coefficient is exploited to evaluate similarity between hashes. Experimental results show that the proposed algorithm is robust against content-preserving operations, such as JPEG compression, watermark embedding, Gamma correction, Gaussian low-pass filtering, adjustments of brightness and contrast, scaling and small angle rotation. Similarity values between hashes of different images are small, indicating good performances in discriminative capability. 相似文献