Study of global ocean wave characteristics based on spaceborne SAR image cross-spectrum
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摘要: 星载合成孔径雷达（Synthetic Aperture Radar, SAR）因其全天时、全天候的观测能力，为全球海洋动力环境要素研究提供了重要数据支撑。然而，SAR海浪成像是非线性过程，现有理论中的近似求解会导致海浪谱反演的信息缺失。SAR图像交叉谱技术的提出一定程度上突破了这一限制，能够很好地量化海浪谱特性及海浪传播方向。本研究延续前人系列成果，利用最新提出的面向径向海浪的图像谱强度，开展不同尺度海浪随局地风速的变化趋势分析，并基于雷达视向图像谱强度提取了谱峰波数，进而结合欧洲空间局环境遥感卫星先进合成孔径雷达波模式在开阔大洋获取的近400万景SAR图像，分析了谱峰波数的全球分布特征，为量化全球风浪耦合过程提供新视角，揭示了海浪与风速耦合关系的空间分布与季节变化规律。
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关键词:
- 星载合成孔径雷达 /
- 欧洲空间局环境遥感卫星先进合成孔径雷达（Envisat/ASAR） /
- 图像交叉谱 /
- 风浪耦合
Abstract: Spaceborne synthetic aperture radar (SAR) is able to collect observations under all kinds of weather during day and night. Such measurements have been proven to provide significant data support for the ocean dynamics study. While SAR imaging of ocean waves is a highly nonlinear process, leading the wave signal missing along the azimuth direction. The image cross-spectrum provides a way to help investigate the ocean wave features particularly for their propagation direction. In this study, we extended a recently defined parameter based on SAR image cross-spectrum and analyzed the correlation of different wave scales with the local wind speed. The range peak wavenumber (wavelength) extracted from the range spectral profile is also demonstrated at the global scale based on about 4 million SAR images. It is found that this new spectral parameter could to some extent reflect the coupling between wind and waves. The global pattern of range peak wavenumber also illustrates evident seasonality. -
图 1 欧洲环境卫星先进合成孔径雷达数据的全球空间分布
a. 空间2.5° × 2.5°统计；b. 月统计
Fig. 1 Global spatial distribution of Envisat/ASAR data
a. Spatial grid of 2.5° × 2.5°; b. monthly data count
图 2 MACS参数定义示意图
a. SAR图像交叉谱，颜色表征归一化图像谱值（蓝色至红色取值0～1）；b. MACS剖面
Fig. 2 Schematic diagram of MACS parameter definition
a. SAR cross-spectrum, color denotes the normalized image spectrum (values from blue to red are 0−1); b. MACS profile
图 3 图像谱参数随风速变化趋势
a. MACS47随风速变化的数据密度，黑色实线为均值及标准差；b. 不同波长MACS随风速变化
Fig. 3 Variation of MACS versus the wind speed
a. Data density of MACS47 relative to wind speed, solid black line indicates the mean and standard deviation; b. variation of MACS at various wavelengths with wind speed
图 4 太平洋150°～145°W间MACS平均剖面随纬度的季节变化
a. 冬季；b. 春季；c. 夏季；d. 秋季
Fig. 4 Seasonal variation of averaged MACS profile over 150°−145°W along the latitude
a. Winter; b. spring; c. summer; d. autumn
图 5 3个选定纬度处的均值图像谱参数剖面（a）及其季节变化（b−d）
Fig. 5 Averaged MACS profile at three selected latitude transects (a) and their seasonal variation (b−d)
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