Ka波段星载海面散射回波多普勒谱分析与质心估计
doi: 10.11728/cjss2026.03.2025-0072 cstr: 32142.14.cjss.2025-0072
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于淼淼 女, 1994年12月出生于黑龙江省, 现为中国科学院国家空间科学中心在读博士, 主要研究方向为先进星载微波遥感定量探测技术等. E-mail: yumiaomiao18@mails.ucas.ac.cn -
朱迪 男, 1978年11月出生于陕西省, 现为中国科学院国家空间科学中心研究员, 博士生导师, 主要研究方向为微波遥感探测与定量信息处理技术等. E-mail: zhudi@mirslab.cn
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Doppler Spectrum Analysis and Centroid Estimation of Ka-band Spaceborne Sea Surface Scatter Echoes
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摘要: 海表动力学参数体现了海洋物质能量平衡、气候变化等重要海气相互作用过程. 在星载测量条件下, 对较高卫星平台运动速度与海表动力学参数共同作用的回波多普勒特性的研究十分必要. 利用线性叠加理论, 建立随时间变化的动态海面模型. 基于全球海表流场多尺度结构观测卫星计划(OSCOM)所拟定的卫星参数, 主要分析风参数对回波多普勒特性的影响. 随着风速的增加, 回波多普勒偏移明显增大. 在顺轨向观测时, 回波多普勒质心偏移量在顺逆风向上略微不对称, 约90°风向时达到最小值. 此外, 当海面风速为10 m·s–1时, 风区长度由不成熟海浪成长为充分发展的海浪时, 长波的倾斜调制增强, 多普勒速度估计相差0.56 m·s–1. 考虑风速为10 m·s–1, 观测方向与风向相同时, 破碎波对Ka波段后向散射系数的贡献. 相比于不考虑破碎波情况的多普勒质心偏移约为71.4 Hz, 导致对径向速度估计相差约为0.3 m·s–1.Abstract: The ocean surface dynamic parameters reflect important air-sea interaction processes, such as the material and energy balance, and climate change. Under spaceborne measurement conditions, it is necessary to study the echo Doppler spectrum characteristics formed by the high operating speed of the satellite in conjunction with the sea surface dynamic parameters. In this paper, a time-varying dynamic sea surface model is established via the existing linear random superposition theory to simulate ocean surfaces. Based on the satellite parameters defined by the Ocean Surface Current multiscale Observation Mission (OSCOM), this work derives echo Doppler spectra involving different wind parameter effects under medium-incidence-angle Bragg scattering conditions. As wind speed increases, the sea surface roughness and root mean square height increase accordingly, resulting in the stronger backscatter modulation, and the echo Doppler shift increases significantly. When observed along the track, the echo Doppler centroid of the Doppler spectrum with wind direction is slightly asymmetric at the downwind and upwind, and reaches a minimum at a 90° wind direction. The analysis results of the wind fetch show that when the wind speed is 10 m·s–1 and the length of wind fetch increases from a-10 km-developing wave to a fully-developed wave, the velocity of the sea surface increases, and the tilt modulation of the long wave increases, resulting in the Doppler shift increases, and the estimated Doppler centroid difference is 0.56 m·s–1. Finally, this study considers the contribution of breaking waves to the co-polarized backscatter and analyzes the influence of both the Doppler centroid and velocity estimation. Analysis of echo Doppler spectrum under the condition of wave breaking shows that when the wind speed is 10 m·s–1 and the observation azimuth is the same as the wind direction, the Doppler centroid offset is about 71.4 Hz, resulting in a deviation of about 0.3 m·s–1 for the radial velocity estimation compared with the case without considering the breaking wave.
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图 1 基于Elfouhaily谱生成的风速10 m·s–1二维动态海面
Figure 1. A two-dimensional dynamic ocean surface with 10 m·s–1 wind speed based on Elfouhaily spectrum
图 2 Ka波段布拉格散射条件下后向散射系数仿真结果
Figure 2. Simulation of backscattering coefficient under Ka-band Bragg scatter condition
图 3 星载海面散射回波多普勒谱仿真流程
Figure 3. Simulation process of Doppler spectra of ocean surface echoed signal onboard
图 4 散射计观测运动海面的网格划分
Figure 4. Grid division for Doppler sacatterpmeter observation of moving ocean surface
图 5 海面回波多普勒谱. (a)仅海面运动产生的多普勒频率, (b)海面运动与平台速度共同作用的结果(去掉平台中心运动速度产生的频率分量), (c)考虑海面后向散射调制影响的多普勒谱
Figure 5. Echo Doppler spectra of Bragg scattering. (a) Only Doppler frequency due to ocean surface motion, (b) ocean surface motion and platform velocity, (c) ocean surface motion, platform velocity and backscattered modulation
图 6 0º观测方位角下不同风速的多普勒谱
Figure 6. Doppler spectra with different wind speeds at 0º azimuth angle
图 7 0º观测方位角下不同风速的多普勒质心与偏差
Figure 7. Doppler centroid and bias with different wind speeds at 0° azimuth angle
图 8 45º观测方位角下不同风速的多普勒谱
Figure 8. Doppler centroid and bias with different wind speeds at 45° azimuth angle
图 9 45°观测方位角下不同风速的多普勒质心与偏差
Figure 9. Doppler centroid and bias with different wind speeds at 45° azimuth angle
图 10 沿顺轨向观测海面风速10 m·s–1时不同风向的多普勒质心
Figure 10. Doppler centroid with different wind directions in along-track direction with a wind speed of 10 m·s–1
图 11 10 m·s–1风速时不同逆波龄对应的波高谱
Figure 11. Wave height spectra with different inverse wave ages at 10 m·s–1 wind speed
图 12 10 m·s–1风速时不同逆波龄的多普勒谱
Figure 12. Doppler spectra with different inverse wave ages at 10 m·s–1 wind speed
图 13 15 m·s–1风速时不同逆波龄的多普勒谱
Figure 13. Doppler spectra with different inverse wave ages at 15 m·s–1 wind speed
表 1 回波多普勒谱仿真参数
Table 1. Simulation parameters of echo Doppler spectrum
参数 数值 载波频率/GHz 35.75 载波波长/cm 0.84 入射角/(º) 46 天线波束宽度/(º) 0.3 卫星轨道高度/ km 520 平台运行速度/(m·s–1) 7000 风速范围/(m·s–1) 7～15 风向范围/(º) 0～180 海表流场速度/(m·s–1) 0.3 海表流场方向/(º) 0 
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