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首页> 外文期刊>IEEE Transactions on Geoscience and Remote Sensing. >On shape, orientation, and structure of atmospheric cells inside wind rolls in two SAR images
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On shape, orientation, and structure of atmospheric cells inside wind rolls in two SAR images

机译：在两个SAR图像中风卷内部的大气单元的形状，方向和结构

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摘要

Synthetic aperture radar (SAR) images of the sea surface often show roll-vortex structures and other features which, in general, are spread out over several length scales and may present spatial periodicity as well as intermittence. Standard techniques, such as two-dimensional (2-D) Fourier analysis, are unsuitable both when it is of interest to detect intermittent phenomena and to analyze the spatial disposition of the backscatter structures inside the SAR images. For the above reasons, the 2-D continuous wavelet transform analysis has been applied to two European Remote Sensing mission SAR images over the Mediterranean Sea, showing wind rolls and atmospheric gravity waves. Through the evaluation of the wavelet variance map, which ideally corresponds to the 2-D Fourier spectrum, it has been possible to assess the presence of two main energy areas at large (from 7-28 km) and small (from 0.5-2 km) spatial scales. While the large-scale fluctuations may be ascribed to atmospheric gravity waves and other features induced by the surroundings, the small-scale fluctuations reveal the inner structure of the atmospheric wind rolls. The SAR-like maps, obtained by adding the wavelet coefficient maps pertaining to the small scales, have permitted us to highlight the high- and low-intensity backscatter cells associated with the wind rolls. These cells have been statistically characterized by means of the frequency distributions of the size of the cells maximum and minimum axes, of the orientation of the maximum axis, and of their area. The results indicate that high- and low-intensity backscatter cells have similar characteristics in both cases studied: they appear of elliptic shape, with the major axis along the wind roll direction; the average axes ratio is 2.5:1. The frequency distributions of the cell area indicate a continuous distribution of sizes, without significant gaps.
机译：海面的合成孔径雷达（SAR）图像通常显示出涡旋结构和其他特征，这些特征通常分布在多个长度尺度上，并且可能表现出空间周期性和间歇性。当需要检测间歇现象并分析SAR图像内部反向散射结构的空间布置时，标准技术（例如二维（2-D）傅里叶分析）既不适用。由于上述原因，二维连续小波变换分析已应用于地中海上的两个欧洲遥感任务SAR图像，显示了风卷和大气重力波。通过评估理想情况下对应于二维傅立叶频谱的小波方差图，可以评估大（从7-28 km）和小（从0.5-2 km）两个主要能量区域的存在）空间尺度。大范围的波动可能归因于大气重力波和周围环境引起的其他特征，而小范围的波动则揭示了大气风卷的内部结构。通过将与小尺度相关的小波系数图相加而获得的类似于SAR的图，使我们能够突出显示与风卷相关的高强度和低强度反向散射像元。这些单元已经通过单元最大和最小轴的尺寸，最大轴的方向及其面积的频率分布进行了统计表征。结果表明，在两种情况下，高强度和低强度反向散射电池都具有相似的特征：它们呈椭圆形，长轴沿风向滚动；平均轴比为2.5：1。单元区域的频率分布表示大小的连续分布，没有明显的间隙。

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