Studies of dual polarized low grazing angle radar sea scatter innearshore regions

Reports on experiments featuring horizontally (HH) and vertically (VV) polarized X-band marine radar sea scatter imagery in the coastal environments of Bermuda and La Jolla, under light to moderate winds and the absence of long gravity waves. These conditions allowed the study of fundamental scattering mechanisms from small scale roughness and short waves of a few meters wavelength or less, shorter than the radar pulse. While a large fraction of radar data collected revealed the presence of slick bands, the authors analyze the radar echo of ambient background outside of the slicks. Sea scatter data were digitally recorded for 360° azimuthal coverage for grazing angles between 1-3.5°, and were converted to normalized radar cross section (NRCS or σ°) images. The HH and VV polarizations show quite different spatial texture, with HH exhibiting a discrete character and VV being more nearly spatially homogeneous. Grazing angle dependencies are different for HH and VV: upwind-downwind differences of mean NRCS show ratios of just 4-6 dB for VV, but are equal or greater than the 16-dB noise-imposed limit for HH for the low wind conditions. HH NRCS grazing angle characteristics are shown to correlate with biological activity indicators of the coastal waters, with a fourth power dependence in relatively unproductive waters, to a nearly quadratic in productive waters. Arguments are presented that suggest different scattering mechanisms for the two polarizations: evenly distributed Bragg scatter patches for VV and scatter from small asymmetric bore features for HH. A multipath illumination model for small bore features is outlined, and scale sizes for the small scale breakers inferred from the experimental results presented are between 2 and 4 cm in height, with crest widths between 24 and 48 cm     

基于实测数据的分时全极化雷达海杂波分布研究

首先基于IPIX分时全极化雷达的海杂波实测数据,分析了瑞利分布、韦布尔分布、对数正态分布和K分布对实测数据的拟合效果,发现对数正态分布拟合水平极化接收通道的杂波数据效果较好,K分布拟合垂直极化接收通道的杂波数据效果较好,但是仍然存在海杂波"拖尾"区域拟合不理想的情况.为此,假设海杂波中的布拉格散射体的回波服从K分布,离散海尖峰的回波服从对数正态分布,海杂波整体服从K分布和对数正态分布的叠加混合分布,提出了一种具有闭式表达式的混合分布,以改善海杂波分布"拖尾"部分的拟合效果.实测数据分析表明,本文提出的混合分布对海杂波幅度分布的拟合效果优于对数正态分布和K分布.     

Measurement of oceanic wind speed from HF sea scatter by skywave radar

Remote measurements of the spatial mean ocean wind speeds were obtained using Doppler spectra resolved to 0.08 Hz from high-resolution HF skywave-radar backscatter measurements of the ocean surface. A standard deviation of 2.4 m/s resulted from the correlation of observed winds over the ocean and the broadening of the Doppler spectra in the vicinity of the higher first-order Bragg line. This broadening, for Doppler spectra unperturbed by the ionospheric propagation, is proportional to the increase in power caused by higher order hydrodynamic and electromagnetic effects in the vicinity of the Bragg line and inversely proportional to the square root of the radio frequency. A lower bound on the measure of wind speed was established at 5 m/s by the low resolution spectral processing and low second-order power. An upper limit is suggested by the steep slope in the region of the sea backscatter spectrum outside the square root of two times the first-order Bragg line Doppler.     

非相干散射雷达探测空间碎片实验研究

这是我国首次用欧洲非相干散射雷达探测空间碎片的实验。根据非相干散射探测原理和空间碎片高度分布的规律,采用匹配滤波方法处理了2010年3月25日15小时实验数据,每小时平均24个碎片,用统计方法分析了碎片高度分布。结果表明:大部分碎片分布在高度为800~1000 km之间,与碎片高度分布理论一致,与中国科学院国家天文台空间碎片预测理论模型比对,比较2010年3月25日10点31分05秒目标信息,高度误差仅为0.97 km,确认为碎片国际标识为1965-016F的美国报废业余通信卫星,证实了非相干散射雷达设备直接探测碎片的可行性。     

基于地物散射模型的空基雷达回波信号研究

从工程应用的角度入手,研究了环境影响下的雷达回波信号模型.介绍了基于地物散射模型生成多普勒波束锐化(DBS)参考图的方法,以某机场光学图为原始图,运用该模型生成了模拟回波和DBS参考图.     

一种极化测量雷达的角闪烁抑制方法

角闪烁是雷达目标的固有特性.以半波振子对为目标模型,利用相位畸变理论,研究了目标在极化测量条件下的角闪烁特性.建立了半波振子对目标在单极化和全极化接收条件下的角闪烁模型,在此基础上提出了一种极化测量雷达的角闪烁抑制方法.理论分析表明,该方法可明显降低目标的角闪烁线偏差.     

Theory and practice of ionosphere study by Thomson scatter radar

The application of Thomson (or incoherent) Scatter observations to the study of the earth's ionosphere is described. Those aspects of theory of Thomson Scatter that have been put to practical use in ionospheric investigations are reviewed briefly and the type of radar equipment constructed for these investigations is discussed. Methods of measuring electron density, electron and ion temperatures, and ionic composition are then reviewed. Other applications of the technique--to the study of the neutral density and temperature of the upper atmosphere, drift motions, the flux density of fast photoelectrons, and the orientation of the earth's magnetic field--are also described.     

An ultrafast wide-band millimeter-wave (MMW) polarimetric radar for remote sensing applications

With the advent of high-frequency radio frequency (RF) circuits and components technology, millimeter-wave (MMW) radars are being proposed for a large number of military and civilian applications. Accurate and high-resolution characterization of the polarimetric radar backscatter responses of both clutter and man-made targets at MMW frequencies is essential for the development of radar systems and optimal detection and tracking algorithms. Toward this end, a new design is developed for ultrafast, wide-band, polarimetric, instrumentation radars that operate at 35 and 95 GHz. With this new design, the complete scattering matrix of a target (magnitude and phase) can be measured over a bandwidth of 500 MHz in less than 2 /spl mu/s. In this paper, the design concepts and procedures for the construction and calibration of these radars are described. In addition, the signal processing algorithm and data-acquisition procedure used with the new radars are presented. To demonstrate the accuracy and applicability of the new radars, backscatter measurements of certain points and distributed targets are compared with their analytical radar cross section (RCS) and previously measured /spl sigma//spl deg/ values, respectively, and good agreements are shown. These systems, which can be mounted on a precision gimbal assembly that facilitates their application as high-resolution imaging radar systems, are used to determine the MMW two-way propagation loss of a corn field for different plant moisture conditions.     

Phase calibration of polarimetric radar images

The problem of phase calibration between polarization channels of an imaging radar is studied. The causes of various types of phase errors due to the radar system architecture and system imperfections are examined. A simple model is introduced to explain the spatial variation in phase error as being due to a displacement between the phase centers of the vertical and horizontal antennas. It is also shown that channel leakage can cause a spatial variation in phase error. Phase calibration using both point and distributed ground targets is discussed and a method for calibrating phase using only distributed target is verified, subject to certain constraints. Experimental measurements using the NADC/ERIM P-3 synthetic-aperture radar (SAR) system and NASA/JPL DC-8 SAR, which operates at C-, L-, and P-bands, are presented. Both of these systems are multifrequency, polarimetric, airborne, SAR systems.<>     

Calibration of bistatic polarimetric radar systems

A calibration technique for laboratory type polarimetric, bistatic instrumentation radars is presented. It describes the errors induced by the standard radiation transfer approach (I-SRT) in a way similar to that for the monostatic case. A 12-term error correction and absolute polarimetric calibration is performed with two external reference targets. Only the polarimetric bistatic reference of the first target must be theoretically determined. The scattering reference of the second target is determined by a measurement during the calibration process (single reference calibration). The simulation of a third cross-polarization measurement is performed by an antenna rotation and a remeasurement of the second target. Thus all data are gained for the determination of the error terms and measurements of unknown objects can be full polarimetrically calibrated. The procedures are shown for an adapted dihedral corner reflector. Misalignment errors are discussed     

基于多测量向量模型的极化探地雷达成像算法

针对极化探地雷达( GPR)工作过程中目标成像空间的联合稀疏性,提出了一种基于多测量向量模型的极化探地雷达成像算法。在建立极化探地雷达回波信号模型的基础上,利用各极化通道测量数据的联合稀疏性将各个极化通道的测量数据等效成多测量向量( MMV ),通过多任务贝叶斯压缩感知( MT-BCS)算法对各个极化通道的测量数据进行联合处理从而实现各个极化通道对应的探测场景反射率的重建。基于时域有限差分( FDTD)法的仿真数据处理结果表明所提成像算法在目标位置重建的准确性和背景杂波抑制能力上均优于单测量向量( SMV)模型的极化探地雷达成像算法。     

A convenient technique for polarimetric calibration ofsingle-antenna radar systems

A practical technique for calibrating single-antenna polarimetric radar systems is introduced. This technique requires only a single calibration target such as a conducting sphere or a trihedral corner reflector to calibrate the radar system, both in amplitude and phase, for all linear polarization configurations. By using a metal sphere, which is orientation independent, error in calibration measurement is minimized while simultaneously calibrating the crosspolarization channels. The antenna system and two orthogonal channels (in free space) are modeled as a four-port passive network. Upon using the reciprocity relations for the passive network and assuming the crosscoupling terms of the antenna to be equal, the crosstalk factors of the antenna system and the transmit and receive channel imbalances can be obtained from measurement of the backscatter from a metal sphere. For an X-band radar system with cross polarization isolation of 25 dB, comparison of values measured for a sphere and a cylinder with theoretical values shows agreement within 0.4 dB in magnitude and 5° in phase. An effective polarization isolation of 50 dB is achieved using this calibration technique     

Segmentation of polarimetric synthetic aperture radar data

A statistical image model is proposed for segmenting polarimetric synthetic aperture radar (SAR) data into regions of homogeneous and similar polarimetric backscatter characteristics. A model for the conditional distribution of the polarimetric complex data is combined with a Markov random field representation for the distribution of the region labels to obtain the posterior distribution. Optimal region labeling of the data is then defined as maximizing the posterior distribution of the region labels given the polarimetric SAR complex data (maximum a posteriori (MAP) estimate). Two procedures for selecting the characteristics of the regions are then discussed. Results using real multilook polarimetric SAR complex data are given to illustrate the potential of the two selection procedures and evaluate the performance of the MAP segmentation technique. It is also shown that dual polarization SAR data can yield segmentation resultS similar to those obtained with fully polarimetric SAR data     

Game theoretic design for polarimetric MIMO radar target detection

Polarimetric radar systems allow the flexibility of transmitting arbitrarily polarized waveforms that match the scattering profiles of the target. Since different types of targets have varying profiles, the advantages of a polarimetric radar system can fully be exploited only when the type of target is accurately estimated. However, accurate estimation requires a significant amount of training data, which can be expensive. We propose a polarimetric design scheme for distributed multiple input multiple output (MIMO) radar target detection. We formulate the selection of transmit polarizations using a game theoretic framework by examining the impact of all possible transmit schemes on the detection performance with different available target profiles (see also Gogineni and Nehorai, 2011 [1]). This approach does not require training data, and we show a significant performance improvement due to the polarimetric design. Other radar design problems can also be solved using this game theoretic approach.     

全极化雷达极化标校技术研究

受各种非理想因素的影响,极化测量雷达难以直接测得目标准确的极化散射矩阵（polarization scattering matrix,PSM）,因此,高精度极化标定是准确获取和利用目标极化信息的基础.本文从极化标校的基本原理出发,建立了PSM测量的误差模型,分析了主要误差因素对PSM测量结果的影响,阐述了无源和有源极化标定方法并对其性能和适用场景进行比较,分析了极化标校器的参数对极化标校精度的影响.分析结果表明,目标的交叉极化分量与极化测量雷达系统的极化隔离度处在相同水平时,目标的交叉极化分量测量结果会明显偏离其真值,通过极化隔离度优于测量系统隔离度无源或有源极化定标体对系统进行标校可以减小系统极化隔离度带来的测量误差.本文工作为极化定标体的研制和全极化测量雷达的系统标校奠定了基础.     

A broadband antenna array for sea scatter measurements

A nonuniformly spaced array of 25 side-terminated vertical half rhombics is synthesized for the entire high-frequency band. The array is to be used for both transmitting and receiving, as a sky-wave Doppler radar for sea scatter measurements. The array has the capability for providing a maximum transmitting-receiving product gain in the order of 60 dB at low take-off angles, a product azimuth pattern with a nominal beamwidth of2deg, a40degsectoral coverage, a final product sidelobe level of -38 dB, and a grating-lobe level of -30 dB.     

Full polarimetric calibration for radar cross-section measurements: performance analysis

Full polarimetric scattering measurements are increasingly required for radar cross-section (RCS) tests. Conventional calibration fails to take into account the small amount of antenna cross-polarization coupling that will be present for any practical antenna. In contrast, full polarimetric calibration takes into account and compensates for the nonideal couplings in the transmit and receive channels and paths. We use an existing full polarimetric calibration procedure and a simulation-based performance to study how well the procedure improves measurement accuracy over conventional calibration under practical measurement conditions.     

W波段数字变极化目标特性测量雷达

提出一种新型的W波段数字变极化目标特性测量雷达.该雷达由两子阵变极化天馈、两通道TR模块与数字处理单元构成, 采用空间波束合成任意极化发射、数字方式实现任意极化接收.通过目标实验结果表明, 该雷达能在多种极化体制下准确提取目标极化散射矩阵, 具备测量目标全极化RCS能力以及可用于目标极化特性分析与研究.     

Incorporation of polarimetric radar images into multisensor datasets

A technique is presented for registering polarimetric synthetic aperture radar (SAR) data to other aircraft and spaceborne data sets. Resampling is done on the full Stokes matrix, allowing full polarization synthesis on the coregistered data set. Analysis of data acquired over Pisgah Crater in the Mojave Desert, CA, as part of the Mojave Field Experiment shows that the resampling does not seriously affect the pedestal heights of polarization signatures or estimates of RMS heights for smooth to moderately rough surfaces     

Calibration of polarimetric radar systems with good polarizationisolation

A practical technique is proposed for calibrating single-antenna polarimetric radar systems using a metal sphere plus any second target with a strong cross-polarized radar cross section. This technique assumes perfect isolation between antenna ports. It is shown that all magnitudes and phases (relative to one of the like-polarized linear polarization configurations) of the radar transfer function can be calibrated without knowledge of the scattering matrix of the second target. Comparison of the values measured (using this calibration technique) for a tilted cylinder in the X-band with theoretical values shows agreement within ±0.3 dB in magnitude and ±5° in phase. The radar overall cross-polarization isolation was 25 dB. The technique is particularly useful for calibrating a radar under field conditions, because it does not require the careful alignment of calibration targets