水下地形SAR成像与潮流场的相关性分析示例

The correlation analysis of underwater topography SAR imaging and tidal current

潮流是水下地形SAR成像的决定性因素之一,潮流的周期性变化使水下地形SAR成像与潮流场有密切的关系,同一水下地形不同时刻SAR影像不同。以台湾浅滩为例,基于5景不同时相的ERS-2SAR影像和台湾浅滩实测水深数据,开展了水下地形SAR成像与潮流场的相关性分析。为了排除SAR影像自身成像质量对研究的影响,首先对5景SAR影像的成像质量进行评价,然后通过潮汐潮流数值计算确定SAR成像时刻的潮流场以及基于QuikScat散射计数据确定SAR成像时刻的海面风向。在上述基础上开展了SAR影像后向散射系数与实测水深的相关性分析,总结出水下地形SAR成像与潮流场的关系,结果表明,潮流场与水下地形SAR成像密切相关,当潮流流向与水下地形梯度方向一致或接近时,水下地形SAR成像效果最佳;对于同一水下地形,流向相反的两种潮流对应的SAR影像后向散射系数恰好相反,即SAR影像中的明暗条纹不同。相对于潮流流向的顺流与逆流风向的不同对水下地形SAR成像无影响。

Atidal current is one of the main factors of underwater topography SAR imaging,and the underwater topography SAR imaging is related to the tidal current because of its periodic variability.The SAR images of the same topography acquiring at different time are different.Taking the Taiwan Shoal as study area,five scenes of ERS-2 SAR images are acquired at different time,and the in situ measured water depth is used in the correlation analysis of the tidal current and the underwater topography SAR imaging.These five SAR images are evaluated firstly by the traditional image evaluation method to avoid the influence of SAR imaging factors them selves on the underwater topography SAR imaging.Then the tidal current field of the SAR imaging is determined by the tide and tidal current numerical simulation,and the wind direction is obtained by the QuikSCAT.Based on the above work,the correlation between a SAR backscattering coefficient and the in situ measured water depth is analyzed,and the relation between the underwater topography SAR imaging and the tide time is concluded.The result shows that the underwater topography SAR imaging has closely relation to the tidal current filed,and the SAR image of the underwater topography is best when the direction of the tidal current is close to the grads direction of the water depth.The backscattering coefficients of two SAR images of the same topography acquired on the condition of two opposite tidal current directions is opposing,i.e.,the bright-dark stripes are reverse.Furthermore,fair wind or head wind related to the tidal current direction have no influence on the underwater topography SAR imaging.