星载多普勒散射计地面回波的多普勒谱分析
doi: 10.11728/cjss2025.06.2024-0182 cstr: 32142.14.cjss.2024-0182
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陈少涵 男, 1999年出生于山东省青岛市, 现为中国科学院大学国家空间科学中心硕士研究生, 主要从事微波遥感探测技术等方面的研究. E-mail: chenshaohan21@mails.ucas.ac.cn -
董晓龙 男, 1969年出生于陕西省渭南市, 现为中国科学院大学国家空间科学中心研究员, 博士生导师, 主要从事新型微波遥感探测与成像及微波遥感信息获取的方法与技术研究. E-mail: dongxiaolong@mirslab.cn
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Doppler Spectrum Analysis of Ground Echoes from Spaceborne Doppler Scatterometer
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摘要: 流场多普勒的定标和定量化测量是实现流场观测的基础和前提, 是需要解决的关键核心问题. 建立地面散射回波仿真模型, 对潜在可用于多普勒散射计外定标的自然地面扩展目标的多普勒谱特性进行仿真分析, 比较其在不同平台的运动速度、入射角、方位角下的变化特征. 结果表明, 平台运动速度是影响多普勒谱特性的主要因素, 入射角和方位角的变化也对多普勒谱特性有明显影响. 对不同高度起伏的地面扩展目标的多普勒谱特性仿真结果表明, 高度起伏越大的目标其多普勒谱偏移越大, 同时中心高度的变化对于多普勒谱特性的影响则不明显. 因此在定标目标的选择中, 应选择较为平坦的扩展目标. 最后对地面回波多普勒频偏进行了分析, 并使用DEM模型进行验证. 研究结论将为多普勒散射计定标的后续研究提供支持.Abstract: Sea surface current fields are important oceanic and climatic variables. Due to its capability for global coverage and direct observation of sub-mesoscale sea surface current fields, the Doppler scatterometer has become a frontier in ocean remote sensing technology research. The calibration and quantitative measurement of the Doppler scatterometer are the foundations and prerequisites for current field observations, as well as a critical core issue that needs to be addressed. This paper develops a ground-scatter-echo simulation model and uses it to simulate and analyze the Doppler spectra of natural extended targets that could potentially serve for Doppler scatterometer calibration. First, the variation characteristics of the Doppler spectrum were compared with different platform velocities, incidence angles, and azimuth angles. The results indicate that platform motion speed is the primary factor affecting Doppler spectrum characteristics, while variations in incident and azimuth angles also have significant impacts. Then, the Doppler spectral characteristics of ground extended targets were analyzed with different terrain-undulation conditions, namely varying height variation and central height. Simulation results indicate that targets with larger height variation exhibit greater Doppler spectral frequency shifts, whereas changes in central height have little effect on the Doppler spectral characteristics. Therefore, in the selection of calibration targets, relatively flat extended targets should be chosen, while the absolute elevation of the target is not a critical factor. Finally, an analysis of the ground echo Doppler frequency shift was conducted and validated using the DEM model. The findings of this study will provide support for further research on Doppler scatterometer calibration.
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图 1 地面散射回波多普勒谱仿真流程
Figure 1. Simulation flowchart of ground scattering echo Doppler spectrum
图 21 不同方位角的多普勒频率偏移量及其不确定度
Figure 21. Doppler frequency shift and its uncertainty with different azimuth angles
表 1 旋转笔形波束多普勒散射计参数
Table 1. Parameters of rotating pencil-beam Doppler scatterometer
平台高度/km 520 平台速度/m·s–1 7000 波束宽度/(°) 0.3 脉冲宽度/μs 50 脉冲重复时间/μs 100 入射角/(°) 46 采样率/MHz 20 信号频率(Ka波段)/GHz 35.6 极化方式 VV 刈幅范围/km >1000 
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