Research on the spectral width of the X-band radar clutter backscattered from sea surface
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摘要: 海面电磁回波频谱宽度与海浪波高密切相关，可应用频谱宽度进行海浪有效波高反演。本文应用线性滤波法仿真出了海表散射面元在雷达视向上的投影速度，建立了回波谱宽模型，分析了雷达空间分辨率、回波时间序列长度及海洋环境参数等因素对频谱宽度的影响，同时还针对如何在实际观测过程中选择回波时间序列长度、观测方位角等参数进行了讨论。最后还将理论结果与CSIR-X波段雷达实测数据谱宽估计结果进行了比较。结果表明，剔除雷达噪声以及频率泄露的影响后，基于高斯分布标准偏差的谱宽估计方法所得结果与理论结果吻合很好，这从而证明了理论结果的可靠性。本文所得结果对海浪有效波高反演具有一定参考价值。Abstract: The spectral width of the electromagnetic scattering from sea surface is closely related to the SWH (significant wave height), and thus the spectral width can be used to retrieve the SWH. In this paper, the linear filtering method is employed to simulate the radial velocity of the orbit velocity of the each scattering element on sea surface. Based on the radial velocity, we establish a spectral width model, and analyze the influences of spatial resolution, time sampling length and SWH on spectral width. At the same time, we also discuss how to select the parameters such as time sampling length and the azimuth angle during the actual observation. Here, the theoretical results are compared with the estimated results based on the measured data required by the CSIR-X band radar. The comparisons demonstrate that the spectral width obtained by the estimation method based on Gaussian distribution standard deviation agree well with the theoretical results after eliminating the effects of radar noise and frequency leakage, which proves the reliability of the theoretical results. The results obtained in this paper have certain reference value for the retrieval of the SWH.
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Key words:
- sea surface simulation /
- sea clutter /
- Doppler characteristics /
- spectrum width
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图 1 雷达空间分辨率、回波时间采样长度和海浪波高对谱宽的影响
Fig. 1 The influences of spatial resolution, time sampling length and wave height on spectral width
图 2 雷达方位角、海浪有效波高等因素对不同入射角回波谱宽的影响（
${\rho _{{t}}} = 15\;{\rm{s}}$ ，${\rho _x} = {\rho _y} = 200\;{\rm{m}}$ ）Fig. 2 For different radar incident angle, the influences of azimuth angle and effective wave height on spectral width (
${\rho _{{t}}} = 15\;{\rm{s}}$ ，${\rho _x} = {\rho _y} = 200\;{\rm{m}}$ )
图 3 雷达方位角、海浪有效波高等因素对不同入射角回波谱宽的影响（
${\rho _{{t}}} = 1\;{\rm{s}}$ ，${\rho _x} = {\rho _y} = 15\;{\rm{m}}$ ）Fig. 3 For different radar incident angle, the influences of azimuth angle and effective wave height on spectral width (
${\rho _{{t}}} = 1\;{\rm{s}}$ ,${\rho _x} = {\rho _y} = 15\;{\rm{m}}$ )
图 4 不同回波时间序列时，Q值随Doppler频率变化
Fig. 4 The value of Q with the Doppler frequency for different T
图 5 不同估计方法所得谱宽随波高的变化
Fig. 5 For different estimation methods, the value of spectral width with wave height
图 6 不同的谱宽估计方法结果和理论结果的比较
Fig. 6 Comparison of the theoretical results with spectral width
图 7 不同回波时间序列及观测条件下的功率谱
Fig. 7 Power spectrum under different time series and observation
图 8 不同观测条件下，长时谱宽与短时谱宽的散点图
Fig. 8 Comparison scatter plots between the spectral width for T=30 s and for T=1 s for different observation
表 1 实测样本数据参数信息
Tab. 1 Measured sample data parameter information
数据集 距离单元 掠射角
/（°）方位角
$\varphi /$（°）有效波高
H/mDataset_08_069_CStFA 37～49 6.86～16.6 0 2.14 Dataset_09_011_TTrFA 68～80 5.56～10.6 0 2.83 Dataset_06_093_CStFA 33～70 6.86～16.6 0 2.91 Dataset_02_029_CStFA 19～34 7.28～14.6 0 3.00 Dataset_06_064_TTrFA 24～37 6.14～12.9 0 3.22 Dataset_05_081_CStFA 20～88 6.86～16.6 0 3.33 Dataset_05_027_CStFA 39～59 6.86～16.6 0 3.68 
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表 2 线性方程的参数a、b
Tab. 2 Parameters a, b of the linear equation
谱宽 a b 理论模拟谱宽 8.55 18.84 $\Delta {f_1}$ 10.30 17.81 $\Delta {f_2}$ 8.56 17.55 $\Delta {f_3}$ 8.70 12.21
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表 3 实测结果与理论结果之间的偏差与标准偏差
Tab. 3 Deviation and standard deviation between measured results and theoretical results
比较方式 偏差 标准偏差 $\Delta {f_1}$与理论结果 4.58 3.47 $\Delta {f_2}$与理论结果 -1.09 1.98 $\Delta {f_3}$与理论结果 -6.01 5.58
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