Speckle Noise Spectrum at Near-Nadir Incidence Angles for a Time-Varying Sea Surface
Speckle Noise Spectrum at Near-Nadir Incidence Angles for a Time-Varying Sea Surface
复制标题
DOI：
10.1109/tgrs.2020.3037910
复制
发表时间：
2022
影响因子：
8.2
通讯作者：
Ping Chen;D. Hauser;Shihao Zou;Jianyang Si;E. Le Merle
中科院分区：
文献类型：
--
作者：
Ping Chen;D. Hauser;Shihao Zou;Jianyang Si;E. Le Merle
散斑噪声是雷达测量所固有的。对于既需要高时间分辨率又需要高空间分辨率的应用，通过过滤反向散射信号来减少斑点噪声的经典方法可能是不够的。特别地，当雷达观测被用于从给定覆盖区内的雷达信号的相对波动来估计海浪谱时，必须实现一种方法来校正傅立叶域中的散斑效应（即，密度谱）。杰克逊于1981年提出了一种模拟近天底入射雷达斑点密度谱的理论背景，但它是基于平稳海面假设，忽略了原点附近四频矩中主要因子的变化。在这篇文章中，我们重新审视这一理论背景，将这一模型扩展到时变海面，并减轻了菲涅耳相位公式的一些假设。将该模型应用于某机载系统配置中的结果表明，在某些观测方向上，不仅雷达的位移而且海面的动力学特性对斑点噪声谱都有显著的影响。这些影响取决于雷达的方位角观测方向和海面条件（风速、相对于飞机航线的风向、表面波频谱）。这个新的模型进行了验证，对机载近天底入射散射仪Ku波段雷达观测表面（KuROS）的观测。我们特别表明，从KuROS的全向散斑噪声谱的实验估计和我们的模型的预测之间的误差低于10%。
Speckle noise is inherent to radar measurements. For applications which need both a high temporal and high spatial resolution, a classical method for the reduction of the speckle noise by filtering the backscattered signal may not be sufficient. In particular, when radar observations are used to estimate ocean wave spectra from relative fluctuations of the radar signal within a given footprint, a method must be implemented to correct for the speckle effect in the Fourier domain (i.e., density spectrum). A theoretical background to model the speckle density spectrum for a radar with near-nadir incidences was proposed by Jackson in 1981 but it is based on a stationary sea surface assumption and ignores the variation of the main factor in the four-frequency moment near the origin. In this article, we revisit this theoretical background to extend this model to a time-varying sea surface and alleviate some assumptions on the Fresnel phase formulation. The results from the model applied in the configuration of an airborne system indicate that not only the displacement of the radar but also the dynamic properties of the sea surfaces have a significant effect on the speckle noise spectrum in certain directions of observations. The effects depend on the radar look direction in azimuth, and on sea surface conditions (wind speed, wind direction with respect to the aircraft route, surface wave spectrum). This new model is validated against observations of the airborne near-nadir incidence scatterometer—Ku-band Radar for Observation of Surfaces (KuROS). We show in particular that the errors between the experimental estimation of the omni-directional speckle noise spectrum from KuROS and the prediction by our model are below 10%.