合成孔径雷达图像反演海面风向新方法的研究

A new research on sea surface wind direction retrieval of synthetic aperture radar image

提出了利用基于Tikhonov正则化的二维数值微分方法来反演合成孔径雷达图像海面风向的新方法.首先将高分辨率合成孔径雷达图像去噪、降采样并分割成数个子图像,利用基于Tikhonov正则化的二维数值微分方法求解所关注子图像每一个点的梯度方向,在此基础上通过带有距离权重的目标函数确定子图像整体强度的梯度方向,该梯度的垂线方向就是所要求解的风向,然后进行模拟试验,在添加误差为10%的随机扰动情况下,分别基于Tikhonov正则化的二维数值微分方法与基于有限差分的Sobel算子方法来反演风向,结果表明,前者误差为0.7293°,后者误差为13.5069°,最后进行了实例试验,结果显示,Sobel算子方法的部分风向反演结果偏离整体风向明显,而基于Tikhonov正则化的二维数值微分方法的风向反演结果一致性较好.将三个船舶报风向与相应位置合成孔径雷达图像的海面风向反演结果进行对比,Sobel算子方法的风向反演结果平均误差在9.0331°,而基于Tikhonov正则化的二维数值微分方法的风向反演结果平均误差仅为1.1148°.

A new method to retrieve sea surface wind direction using synthetic aperture radar image is presented.Some pretreatment steps such as suppressing noise,down sampling and dividing into several sub-images are presented first.The method of two-dimensional numerical differentiation based on Tikhonov regularization is introduced to compute the gradient direction in the sub-image intensity of every point.The distance weighted objective function is used to compute the overall gradient direction in the sub-images.The retrieved wind direction is orthogonal to the overall gradient.When adding 10% of random errors,numerical simulations show that the result of numerical differentiation is better than that from the Sobel operator which is based on the finite difference method：the former error is 0.7293 °,and the latter error is 13.5069 °.Finally,an experiment based on real SAR data shows that the wind direction deviates from the overall direction determined by the method of Sobel operator,and the direction determined by the method of numerical differentiation is consistent well with the overall wind direction.Comparing the ship board wind direction and the corresponding location wind direction retrieved from the synthetic aperture radar sub-images with the two methods,the average result error of Sobel operator method is 9.0331°,while that of numerical differentiation method is 1.1148°.This new method is an effective and high accurate method to retrieve the sea surface wind direction of synthetic aperture radar image.