First order sea clutter cross section for bistatic shipborne HFSWR

This paper studies the development on the first order sea clutter cross section for bistatic high frequency surface wave radar (HFSWR). Based on the received first order electric field expression, a closed-form of cross sections is derived to account for the case of receiving antenna array being mounted on the shipborne platform. The uniform linear motion and sway motion components are assumed to be responsible for the observed differences in comparison with the bistatic fixed antenna case. Correspondingly, simulations are conducted to study the sea clutter spectral characteristics for these two cases versus different system parameters and sea state conditions. It is shown numerically that the forward motion component will spread the Bragg lines severely and the influence triggered by the sway motion can be explained as the Bessel function modulation of the ordinary sea clutter spectra. The obtained results have important implications in the application of shipborne HFSWR technology to ocean remote sensing and target detection.

Microwave characteristic simulation research for a kind of novel electromagnetic structure

A kind of novel electromagnetic structure of Cassini cross section is proposed and simulation is implemented with business microwave soft CST based on finite integral technique （FIT）. The electromagnetic field mode type of Cassini wave-guide belongs to TE, and the electromagnetic field intensity is stronger near the neck region than at other areas. For Cassini electromagnetic patches and lumped elements, the radar cross section （RCS） is smaller around 7 GHz with -30.85 dBsm, and the absorbing property is better around 13 GHz with 4.56 dBsm difference of RCS from comparing of pure medium. For novel radiation structure of Cassini cross-section patches, the electromagnetic field value is larger in the neck areas of two half patches. At last, the potential application and development of Cassini oval structure are put forward in the electromagnetic stealth technology and antennae design.

Study of the ability of SWOT to detect sea surface height changes caused by internal solitary waves

Surface Water and Ocean Topography(SWOT)is a next-generation radar altimeter that offers high resolution,wide swath,imaging capabilities.It has provided free public data worldwide since December 2023.This paper aims to preliminarily analyze the detection capabilities of the Ka-band radar interferometer(KaRIn)and Nadir altimeter(NALT),which are carried out by SWOT for internal solitary waves(ISWs),and to gather other remote sensing images to validate SWOT observations.KaRIn effectively detects ISW surface features and generates surface height variation maps reflecting the modulations induced by ISWs.However,its swath width does not completely cover the entire wave packet,and the resolution of L2/L3 level products(about 2 km)cannot be used to identify ISWs with smaller wavelengths.Additionally,significant wave height(SWH)images exhibit blocky structures that are not suitable for ISW studies;sea surface height anomaly(SSHA)images display systematic leftright banding.We optimize this imbalance using detrending methods;however,more precise treatment should commence with L1-level data.Quantitative analysis based on L3-level SSHA data indicates that the average SSHA variation induced by ISWs ranges from 10 cm to 20 cm.NALTs disturbed by ISWs record unusually elevated SWH and SSHA values,rendering the data unsuitable for analysis and necessitating targeted corrections in future retracking algorithms.For the normalized radar cross section,Ku-band and four-parameter maximum likelihood estimation retracking demonstrated greater sensitivity to minor changes in the sea surface,making them more suitable for ISW detection.In conclusion,SWOT demonstrates outstanding capabilities in ISW detection,significantly advancing research on the modulation of the sea surface by ISWs and remote sensing imaging mechanisms.

RCS analysis in the detection of a generic missile target with sea clutter background

The detection of a missile target in heavy sea clutter is a significantly challenging problem due to the clutter effects. In this paper, the radar cross sections(RCS) of a pre-assumed generic missile model is computed with multilevel fast multi-pole algorithm(MLFMA), while the RCS of ocean surface is computed by a more reduced form of the fractional Weierstrass scattering model proposed here. At last, the computed RCS of missile model is compared with that of sea surface, and then the comparisons of missile-to-ocean RCS ratios of different incident angles, incident frequencies, and polarization patterns are also presented. The discussion and comparisons of RCS of the missile and ocean surface can help us to plan and design a radar system in the application of detection of a missile target or other analogous weaker targets in the strong sea clutter background.

First assessment of Noise-Equivalent Sigma-Zero in GF3-02 TOPSAR mode with sea surface wind speed retrieval

Gaofen-3-02(GF3-02)is the first C-band synthetic aperture radar(SAR)satellite with terrain observation with progressive scans of SAR(TOPSAR)imaging mode in China,which plays an essential role in marine environment monitoring.Given the weak scattering characteristics of the ocean,the system thermal noise superimposed on SAR images has significant interference,especially in cross-polarization channels.Noise-Equivalent Sigma-Zero(NESZ)is a measure of the sensitivity of the radar to areas of low backscatter.The NESZ is defined to be the scattering cross-section coefficient of an area which contributes a mean level in the image equal to the signal-independent additive noise level.For TOPSAR,NESZ exhibits the shape of the SAR scanning gain curve in the azimuth and the shape of the antenna pattern in the range.Therefore,the accurate measurement of NESZ plays a vital role in the application of spaceborne SAR sea surface cross-polarization data.This paper proposes a theoretical calculation method for the NESZ curve in GF3-02 TOPSAR mode based on SAR noise inner calibration data and the imaging algorithm.A method for correcting the error existing in the theoretical curve of NESZ is also proposed according to the relationship between sea surface backscattering and wind speed and the same characteristics of target scattering in the overlapping area of adjacent sub-swaths.According to assessment with wide-swath TOPSAR cross-polarization data,the GF3-02 TOPSAR mode has a very low thermal noise level,which is better than−33 dB at the edge of each beam,and controlled below−38 dB at the center of the beam.The two-dimensional reference curves of the NESZ of each beam are provided to the GF3-02 TOPSAR users.After discussing the relationship between normalized radar cross section(NRCS)and wind speed,we provide a formula for NRCS related to wind speed and radar incidence angle.Compared with the NRCS derived from this formula and the NESZ-subtracted NRCS of SAR images,the bias is−0.0048 dB,the Root Mean Square Error is 1.671 dB and the correlation coefficient is 0.939.

Sea Surface Roughness Derivation from Wind Speed Estimated by Satellite Altimeter

For open sea conditions the sea surface roughness is described as a function of surface stress and wind speed over sea surface by Charnock relation. The sea surface roughnessn in the North-west Pacific Ocean is derived successfully using wind speed data estimated by the TOPEX satellite altimeter. From the results we find that： （1） the mean sea surface roughness in winter is greater than in summer; （2） compared with other sea areas, the sea surface roughness in the sea area east of Japan （ N30°- 40°, E135°- 150°） is larger than in other sea areas; （3） sea surface roughness in the South China Sea changes more greatly than that in the Bohai Sea, Yellow Sea and East China Sea.

基于改进SBR的舰船SAR成像快速仿真计算方法

针对SAR(Synthetic Aperture Radar)舰船成像仿真应用中电磁散射特性计算效率低下的问题,在现有SBR(Shooting and Bouncing Rays)算法的基础上,本文提出两方面改进.一是基于叶节点空间邻域编码搜索的射线管相交面元检测算法,通过只追踪射线管中心射线并搜索叶节点空间周围潜在相交面元,在有效提升相交检测速度的同时避免遗漏相交面元;二是射线管三角剖分快速分裂算法,将射线管和相交面元投影至射线管虚拟孔径面,利用Delaunay三角剖分算法自适应地将射线管快速分裂成连续的子射线管.对典型舰船目标进行RCS(Radar Cross Section)计算及SAR成像仿真实验,结果表明,在保证计算精度的前提下,本文方法计算效率比Kd树(K-dimension tree)加速SBR方法提升14倍以上,比经典自适应射线管分裂SBR方法提升3倍以上,计算效率显著提高.

Retrieval of sea surface winds under hurricane conditions from GNSS-R observations

Reflected signals from global navigation satellite systems（GNSSs） have been widely acknowledged as an important remote sensing tool for retrieving sea surface wind speeds.The power of GNSS reflectometry（GNSS-R）signals can be mapped in delay chips and Doppler frequency space to generate delay Doppler power maps（DDMs）,whose characteristics are related to sea surface roughness and can be used to retrieve wind speeds.However,the bistatic radar cross section（BRCS）,which is strongly related to the sea surface roughness,is extensively used in radar.Therefore,a bistatic radar cross section（BRCS） map with a modified BRCS equation in a GNSS-R application is introduced.On the BRCS map,three observables are proposed to represent the sea surface roughness to establish a relationship with the sea surface wind speed.Airborne Hurricane Dennis（2005） GNSS-R data are then used.More than 16 000 BRCS maps are generated to establish GMFs of the three observables.Finally,the proposed model and classic one-dimensional delay waveform（DW） matching methods are compared,and the proposed model demonstrates a better performance for the high wind speed retrievals.

光电转台RCS仿真研究

通过软件仿真计算光电转台的雷达散射截面积(radar cross section,RCS)。基于散射的高频局部性原理完成目标的RCS预估,在S、C、X波段,0~3°入射余角条件下对光电转台的RCS进行仿真。将复杂的光电转台分解,研究各部分RCS特性并对光电转台开展隐身设计。对完成隐身设计后的转台进行仿真分析,隐身设计后均值大于0.5 m^(2)的RCS占比约为18.18%,光电转台隐身特性提升明显。

基于舰载雷达的海杂波特性分析与仿真

舰载雷达在海面作战中具有重要的作用,对舰载雷达所处的海面环境进行分析,及时将舰载雷达所受到的海杂波的特性进行分析和仿真,能够提高舰载雷达探测目标的准确性。论文首先对海杂波的后向散射特性进行了分析和阐述,之后对于海杂波的后向散射特性进行了建模与仿真。为舰载雷达的海杂波特性分析提供了新的思路。

海面背景下弱目标RCS估计及特性分析

雷达截面积(radar cross section,RCS)可以为武器装备设计提供支撑。因此,许多国家都建立了标准测试场,可以满足大多数目标RCS测量的需要。对于海面背景下的非合作弱目标而言,只能依赖实际测试来获取目标RCS,但有时会面临多径干扰和信号弱的问题。针对该问题,在海上外定标和目标信杂比改善基础上,提出了一种目标RCS估计方法。设计并开展了海上目标RCS测量试验,并对测试数据进行了分析,验证了新方法的有效性,同时给出了弱目标RCS起伏特性的定性描述。

基于GPU并行技术的超大型海面舰船电磁散射仿真

为了解决超电大尺寸海面舰船场景中电磁散射计算的瓶颈问题,研究基于多图像处理单元(Multi-GPU)并行加速技术的弹跳射线法(SBR)。借助统一设备计算架构(CUDA)提供的多线程服务(MPS),构建Multi-GPU并行加速框架,研究基于区域射线束划分GPU计算任务和实现方式;研究基于矩阵网格的任务分割技术,最大限度提高GPU全局内存利用率;针对不同运算单元间的差异所带来的计算不同步问题,设计基于动态负载均衡算法的调度系统,进而提高计算资源利用率。仿真结果表明,在双GPU硬件平台上,该方案与现有并行技术算法相比,在确保结果准确性的情况下加速比接近甚至超过200%。因此,该技术方案能够有效解决超电大海面舰船电磁散射问题。

Exploitation of Electromagnetic Models for Sea Wind Speed Estimation from C-Band Sentinel-1 Images

Among the different available wind sources, i.e. in situ measurements, numeric weather models, the retrieval of wind speed from Synthetic Aperture Radar (SAR) data is one of the most widely used methods, since it can give high wind resolution cells. For this purpose, one can find two principal approaches: via electromagnetic (EM) models and empirical (EP) models. In both approaches, the Geophysical Model Functions (GMFs) are used to describe the relation of radar scattering, wind speed, and the geometry of observations. By knowing radar scattering and geometric parameters, it is possible to invert the GMFs to retrieve wind speed. It is very interesting to compare wind speed estimated by the EM models, general descriptions of radar scattering from sea surface, to the one estimated by the EP models, specific descriptions for the inverse problem. Based on the comparisons, some ideas are proposed to improve the performance of the EM models for wind speed retrieval.

海面雷达散射及其杂波幅度统计特性的空间遍历性数值仿真研究

海面雷达散射的空间遍历性是开展海面散射数值仿真以及分析不同体制雷达系统在海洋遥感应用中算法适用性的重要基础之一。针对随机粗糙海面雷达散射及其杂波幅度统计特性的空间遍历性问题,基于Monte Carlo方法构建包含全部大尺度波浪的粗糙海面模型,利用高精度的全波数值(multilevel steepest decent-sparse matrix canonical grid,MLSD-SMCG)方法以及二阶小斜率近似(2nd-order small slope approximation,SSA-2)模型,分别对不同雷达照射尺寸的一维和二维粗糙海面L波段归一化雷达散射系数及海杂波进行仿真,并对海面雷达散射和海杂波幅度分布的空间遍历性进行分析。仿真结果表明:在无海面遮挡效应的雷达入射和散射角度范围内,雷达照射尺寸大于16λ(入射波波长)粗糙海面的同极化归一化雷达散射系数,具有良好的空间遍历性;当雷达照射海面尺寸不小于对应海况下最大风浪尺度的25%时,海面交叉极化的归一化雷达后向散射系数也表现出空间遍历性。相比海面散射的归一化雷达散射系数,单站海杂波幅度分布在高海况条件下空间遍历性减弱。同极化海杂波幅度分布随着入射角增大,表现出更显著的空间遍历性,而交叉极化情况则相反。

基于海杂波修正的OTHR空中目标RCS估计

天波超视距雷达工作在时变的电离层传输状态下,通过回波能量难以对空中目标的雷达散射截面积(RCS)进行有效估计。为此,提出了一种基于海杂波修正的目标RCS估计方法,建立了RCS估计卡尔曼滤波模型和RCS仿真数据辅助模型。通过两型民航目标的仿真和实测数据验证了所提模型的有效性,其在不同时段、雷达工作状态和电离层传输条件下,实现了对目标RCS和电离层损耗的稳健估计,并利用目标电磁仿真数据进一步辅助提高了对已知类型目标的估计效率和准确性。

舰载近程搜索雷达时空二维海杂波建模与仿真

介绍了海杂波幅度分布、功率谱、时空相关特性对雷达检测的影响和相应的数学建模方法,以舰载近程搜索雷达为研究对象,建立了海杂波仿真模型,最后通过Matlab仿真给出了时空二维海杂波的仿真实现。

RCS测量中聚苯乙烯泡沫支架的电磁散射特性研究

聚苯乙烯泡沫(Expanded PolyStyrene,EPS)支架的电磁散射特性是雷达散射截面(Radar Cross Section,RCS)测量系统性能的关键,直接决定雷达隐身测试精度.针对6种常用EPS支架构型,本文通过建立EPS材料介电参数模型与支架三维模型,开展介质实体建模与电磁仿真研究,并利用RCS测试场进行实验验证,分别对EPS支架的单站/双站、点频/扫频、频域/时域等方面的电磁散射特性进行了深入细致的分析,提出了双菱形锥柱长轴共线与短轴共线相结合的方案,有效改进背景性能.仿真与实测表明,双菱形锥柱构型适用于典型空中目标支撑,尤其可在较大双站角范围内实现-55 dBsm以下的极低散射背景,能够保障隐身目标单/双站测试的背景需求;EPS支架单站RCS对极化特性不敏感,而其双站散射的水平极化明显低于垂直极化.此外,低频段扫频特性起伏振荡达30 dB以上,振荡峰值频率与支架尺寸、位置满足干涉规律.故通过支架设计可使特定频点处于振荡谷值,从而优化低散射背景.本文为RCS测量极低散射背景设计提供了思路及指导.

地杂波背景中的雷达距离方程的研究

对不同分布类型地杂波对雷达检测性能的影响进行了分析,推导了杂波环境中脉冲体制雷达及连续波体制雷达的作用距离方程,讨论了目标雷达截面积与发现距离及发现概率的相互关系,并给出了Matlab仿真实例。

空间目标动态电磁测量数据仿真方法研究

空间目标由于高速运动和微运动在电磁波上的调制效应,其动态实测的雷达散射截面(radar cross section,RCS)和高分辨一维距离像(high resolution range profile,HRRP)与暗室测量或电磁计算数据存在较大的差异。针对空间目标外场动态测量数据难以获取的难题,提出了用目标静态数据生成动态RCS和一维距离像数据的方法。该方法首先确定目标的轨道和雷达的布站坐标及工作模式,而后计算目标在雷达观测视线(line of sight,LOS)方向上的姿态和运动参数,最后根据空间目标高速运动、自旋、进动等在电磁波上调制的数学模型生成动态测量数据。给出了该方法的具体步骤,仿真实验证明了方法的有效性。