On airborne measurement of the sea surface wind vector by a scatterometer (altimeter) with a nadir-looking wide-beam antenna

A pilot needs operational information about wind over sea as well as wave height to provide safety for a hydroplane landing on water. Near-surface wind speed and direction can be obtained with an airborne microwave scatterometer, a radar designed for measuring the scatter characteristics of a surface. Mostly narrow-beam antennas are applied for such wind measurement. Unfortunately, a microwave narrow-beam antenna has considerable size that hampers its placement on flying apparatus. In this connection, a possibility to apply a conventional airborne radar altimeter as a scatterometer with a nadir-looking wide-beam antenna in conjunction with Doppler filtering for recovering the wind vector over sea is discussed, and measuring algorithms of sea surface wind speed and direction are proposed. The obtained result can be interesting for many studies in oceanography, meteorology, air-sea interaction, and climate change and for creation of an airborne radar system for amphibious airplane safe landing on the sea surface, in particular for search and rescue operations in coastal areas.     

利用天线可实现蛋形波束覆盖的机载雷达高度仪测量海风矢量

讨论的是联合利用机载雷达高度仪(拥有可实现蛋形波束覆盖的天底观测宽波束天线)的短脉冲散射仪模式和同时距离多普勒识别技术来测量海面上的海风矢量,并且提出了测量海面风速与方向的算法。     

Wind speed measurement using forward scattered GPS signals

Instrumentation and retrieval algorithms are described which use the forward scattered range-coded signals from the global positioning system (GPS) radio navigation system for the measurement of sea surface roughness. This roughness has long been known to be dependent upon the surface wind speed. Experiments were conducted from aircraft along the TOPEX ground track and over experimental surface truth buoys. These flights used a receiver capable of recording the cross-correlation power in the reflected signal. The shape of this power distribution was then compared against analytical models, which employ a geometric optics approach. Two techniques for matching these functions were studied. The first recognized the most significant information content in the reflected signal is contained in the trailing edge slope of the waveform. The second attempted to match the complete shape of the waveform by approximating it as a series expansion and obtaining the nonlinear least squares estimate. Discussion is also presented on anomalies in the receiver operation and their identification and correction     

Aircraft measurements of the microwave scattering signature of the ocean

Microwave scattering signatures of the ocean have been measured over a range of surface wind speeds from 3 m/s to 23.6 m/s using the AAFE RADSCAT scatterometer in an aircraft. Normalized scattering coefficients are presented for vertical and horizontal polarizations as a function of incidence angle (nadir to55deg) and radar azimuth angle (0degto360deg) relative to surface wind direction. For a given radar polarization, incidence angle, and azimuth angle relative to the wind direction, these scattering data exhibit a power law dependence on surface wind speed. The relation of the scattering coefficient to azimuth angle obtained during aircraft circles (antenna conical scans) is anisotropic and suggests that microwave scatterometers can be used to infer both wind speed and direction. These results have been used for the design of the Seasat-A Satellite Scatterometer (SASS) to be flown in 1978 on this first NASA oceanographic satellite.     

北斗反射信号海风海浪反演系统与试验

该文设计并实现了一种小型低功耗的北斗反射信号海风海浪反演系统,针对反演精度受卫星高度角影响较大的问题,提出高度角正弦值幂指数修正方法,且为降低风速突变对风速反演的影响,对风速反演模型进行了延时修正,有效提高了有效波高和风速的反演精度。为了进一步提高反演精度,提出多星联合观测和单边滤波的方法。北斗反射信号海风海浪探测试验结果表明:设计和实现的反演系统具备长期稳定运行和观测的性能;提出的反演模型和精度提升方法可以有效提高反演精度,有效波高和风速反演精度分别可达0.14 m和1.28 m/s,相比于Soulat等人提出的反演模型,分别提高了0.13 m和0.78 m/s。     

雷达接收机信道对脉冲信号相位谱干扰模型的分析与处理

雷达的接收机信道作为带通滤波器,其内部混有噪声,因此,当用其传输放大脉冲信号时,对脉冲相位谱会产生影响,使脉冲前后沿发生变化。本文分析了雷达信道对脉冲相位谱的干扰模型及影响程度,为消除其影响提供了准确、可靠的理论依据,并提供了处理这类信号的数学模型。     

毫米波捷变频体制下低空风切变风速估计方法

机载气象雷达下视探测低空风切变时,复杂的电磁干扰及强地杂波会严重影响其对目标信号的检测,造成风场速度估计失准。针对上述问题,本文提出一种毫米波（millimeter wave,MMW）捷变频体制下的低空风切变风速估计方法。该方法采用载频脉组间捷变,在每个脉组内利用雷达系统先验信息设计两维两脉冲对消（two dimensional pulse-to-pulse canceller,TDPC）预滤波器对雷达回波进行预滤波,削弱杂波功率,接着利用基于组合空时主通道的自适应处理（combined space-time main channel adaptive processing,CMCAP）对回波数据进行空时二维滤波,得到风切变信号的模糊多普勒估计值,最后将每个脉组内的估计结果由多普勒频率域转换到速度域,采用错位差分查表的方式订正模糊速度,从而得到风场的真实速度值。仿真结果分析验证了所提方法的有效性。      

基于ML4803的两级PFC变换器研究

两级功率因数校正（PFC）变换器因其较高的功率因数而广泛应用于功率因数校正场合。近年来,随着PFC/PWM复合控制芯片的应用,两级功率因数校正技术得到了很大的发展。传统两级PFC采用后缘/后缘调制方法（Trailing Edge Modulation/Trailing Edge Modulation,TEM/TEM）。而现今广泛使用前缘/后缘调制方法（Leading Edge Modulation/Trailing Edge Modulation,LEM/TEM）可有效减小流经连接前级PFC和后级DC/DC阶段的直直连接电容的电流有效值,但尚未有详细的理论推导。文章在两种调制方法下对流经直直连接电容的电流有效值进行了详细的理论分析,并给出了仿真验证。最后,利用复合控制芯片ML4803设计了一台具有功率因数校正功能的两级PFC变换器,对理论仿真分析进行了实验验证。     

L波段气象探空雷达角度自动跟踪系统故障分析

角度自动跟踪系统是气象探空雷达重要组成部分,通过对空中运动气球携带电子探空仪的跟踪将温度、湿度、气压电码发送到雷达接收系统,同时通过测距和跟踪电子探空仪的方位、仰角计算出当前时间的风向、风速,以此来完成气象5个要素的探测。目前,该型号雷达在使用过程中故障率最高的是角度自动跟踪系统。文中根据振幅和差式假单脉冲技术原理、天线传输馈线原理,结合2个典型的故障案例,分析了故障的成因,给出了故障诊断测试方法,为实时气象探空业务提供了可靠保障。     

Polarimetric radar remote sensing of ocean surface wind

Experimental data are presented to support the development of a new concept for ocean wind velocity measurement (speed and direction) with the polarimetric microwave radar technology. This new concept has strong potential for improving the wind direction accuracy and extending the useful swath width by up to 30% for follow-on NASA spaceborne scatterometer mission to SeaWinds series. The key issue is whether there is a relationship between the polarization state of ocean backscatter and surface wind velocity at NASA scatterometer frequencies (13 GHz). An airborne Ku-band polarimetric scatterometer (POLSCAT) was developed for proof-of-concept measurements. A set of aircraft flights indicated repeatable wind direction signals in the POLSCAT observations of sea surfaces at 9-11 m/s wind speed. The correlation coefficients between co- and cross-polarized radar response of ocean surfaces have a peak-to-peak amplitude of about 0.4 and are shown to have an odd-symmetry with respect to the wind direction, unlike the normalized radar cross sections     

Evaluation of surface clutter for the design of the TRMM spaceborneradar

Surface clutter interference through antenna sidelobes on rainfall measurements by spaceborne rain radar is quantitatively examined in order to clarify design criteria for the antenna. The received intensities of both rain echo and sea clutter are evaluated numerically, assuming appropriate precipitation and sea surface scattering models and a realistic antenna pattern for a phased array antenna, which is fed with the Taylor distribution. The results indicate that a region exists just above the sea surface where the sea surface clutter masks the backscattered power from the rain. The results also demonstrate the feasibility of quantitative measurements of rainfall in regions above this interference zone if a planar array antenna fed with the Taylor distribution of peak sidelobe level -30 dB is used     

A C-band scatterometer for remote sensing the air-sea interface

An airborne C-band scatterometer system (C-Scat) has been developed to remotely sense ocean surface winds and improve upon the present understanding of the relationship between normalized radar cross section (NRCS) and ocean surface roughness influences such as wind speed and direction, wave height and slope, and the air-sea temperature difference. The scatterometer utilizes a unique frequency-steered microstrip array antenna that is installed beneath the fuselage of an airplane. The antenna is electronically scanned in elevation, from 20° to 50° off-nadir, and mechanically spins in azimuth. The system is capable of measuring ocean surface NRCS from altitudes as high as 25000 ft. The system is divided into four subsystems: the transmitter and receiver, the spinning antenna, the computer control and data acquisition subsystem, and the digital and analog interface electronics     

基于高频雷达二阶海洋回波的风速反演算法研究与应用

基于高频电磁波与海洋表面的散射机制,以雷达二阶散射截面方程为理论依据。首先,进行了从高频雷达二阶海洋 回波谱中反演饱和风速的算法理论近似,讨论算法运用的前提条件;其次进行了饱和风速与二阶谱峰频率的关系式推导;然后,利用高频地波雷达模拟海洋回波谱数据对算法进行了可行性验证,证明该算法特定风速范围内有较好的反演结果; 最后,将算法应用于实测高频地波雷达海洋回波多普勒谱进行了饱和风速反演,并进行了反演结果分析与误差分析。 结果分析表明:该算法在满足理论近似条件的前提下能有效提取海面饱和风速信息。     

面向目标跟踪的机载组网雷达辐射参数与航迹规划联合优化算法

该文针对机载组网雷达,在单目标跟踪场景下,研究了雷达辐射参数与航迹规划联合优化问题。首先,推导了包含各雷达辐射功率、驻留时间、发射信号高斯脉冲长度和信号带宽等射频辐射参数以及各载机速度、朝向角等平台运动参数的贝叶斯克拉默-拉奥下界(BCRLB)表达式,以此作为表征目标跟踪精度的衡量指标;推导了含有各雷达辐射功率、驻留时间等射频辐射参数以及各载机速度、朝向角等平台运动参数的机载组网雷达被截获概率,以此作为表征机载组网雷达射频隐身性能的衡量指标。在此基础上,建立了面向目标跟踪的机载组网雷达辐射参数与航迹规划联合优化模型,以最小化机载组网雷达的目标估计误差BCRLB为优化目标,以满足给定的系统射频资源、载机机动能力和预先设定的被截获概率阈值为约束条件,对各载机飞行速度、朝向角以及各机载雷达辐射功率、驻留时间、发射信号高斯脉冲长度和信号带宽进行联合优化设计,以提升机载组网雷达的目标跟踪精度。最后,针对上述优化问题,结合粒子群算法,采用5步分解迭代算法进行求解。仿真结果表明,与现有算法相比,所提算法能够在满足一定射频隐身性能要求的条件下,有效提升机载组网雷达的目标跟踪精度。      

A physical model for mode-locking process of colliding pulsemode-locked multiquantum-well semiconductor laser

In this paper, we first present a physical model for mode-locking process of the colliding pulse mode-locked multiquantum-well laser diode (CPM-MQW-LD). The absorption of saturable absorber on pulse leading edge and the scattering of the transient grating generated in absorption and gain regions on pulse trailing edge are considered. As an example, the mode-locking process of a multiquantum-well structure laser and the effect of transient grating on pulse width and peak power are studied     

基于LRMO及MCA的机载雷达风电场杂波抑制方法

风力发电迅速发展,风电场杂波使机载雷达产生大量虚假目标,导致机载雷达出现检测概率下降、虚警概率上升等问题。因此,研究机载雷达风电场杂波抑制方法对于提升机载雷达工作性能具有十分重要的意义。考虑到机载雷达风电场杂波先验信息无法实时获取、难以估计且机载雷达回波频谱更加复杂等特殊问题,本文基于低秩矩阵优化（LRMO）算法根据风电场杂波与目标微动特征随时间的不同变化特性,实现目标与风电场杂波处于不同距离单元的风电场杂波抑制。目标与风电场杂波处于同一距离单元时,考虑到LRMO算法存在的局限性,依据风电场杂波与目标的不同稀疏特性,利用形态成分分析（MCA）算法进行补充抑制风电场杂波。实验结果验证了所提方法的有效性。      

Analysis of weather radar return

A mathematical model of detected clutter from an airborne weather radar of conventional design is developed. The model is the joint probability density of samples of radar return from hydrometeors at the same nominal range and scan angle. It is developed from analysis of the effect on the received signal of the following parameters: inhomogeneous hydrometeor motion, radar frequency stability, pulsewidth, antenna beamwidth, scan angle, scan rate, and aircraft speed. In addition, the influence of finite pulse volume on radar sensitivity to hydrometeor motion is examined.     

A Numerical Study of the Retrieval of Sea Surface Height Profiles From Low Grazing Angle Radar Data

A numerical study of the retrieval of sea surface height profiles from low grazing angle radar observations is described. The study is based on a numerical method for electromagnetic scattering from 1-D rough sea profiles, combined with the “improved linear representation” of Creamer for simulating weakly nonlinear sea surface hydrodynamics. Numerical computations are performed for frequencies from 2975 to 3025 MHz so that simulated radar pulse returns are achieved. The geometry utilized models a radar with an antenna height of 14 m, observing the sea surface at ranges from 520 to 1720 m. The low grazing angles of this configuration produce significant shadowing of the sea surface, and standard analytical theories of sea scattering are not directly applicable. Three approaches for retrieving sea height profile information are compared. The first method uses a statistical relationship between the surface height and the computed radar cross sections versus range (an incoherent measurement). A second method uses the phase difference between scattering measurements in two vertically separated antennas (“vertical interferometry) in the retrieval. The final technique retrieves height profiles from variations in the apparent Doppler frequency (coherent measurements) versus range and requires that time-stepped simulations be performed. The relative advantages and disadvantages of each of the three approaches are examined and discussed.      

布里渊放大修正陡前沿Stokes脉冲波形

研究了受激布里渊散射(SBS)放大池中．通过改变抽运光与Stokes种子光脉冲的延时．改变它们在池中的相遇位置．实现抽运光对陡前沿种子光脉冲不同部位的选择性放大．从而修正Stokes脉冲波形。理论和实验研究了Stokes光脉宽、脉冲波形前后沿时长比以及能量提取效率等参数随相遇时间的变化规律．在相遇时间2．5ns时，理论得到前后沿时长比为1，能量提取效率80%以上的Stokes放大光脉冲波形．理论和实验符合较好。     

Wind direction over the ocean determined by an airborne, imaging,polarimetric radiometer system

The speed and direction of winds over the ocean can be determined by polarimetric radiometers. This has been established by theoretical work and demonstrated experimentally using airborne radiometers carrying out circle flights and thus measuring the full 360° azimuthal response from the sea surface. An airborne experiment, with the aim of measuring wind direction over the ocean using an imaging polarimetric radiometer, is described. A polarimetric radiometer system of the correlation type, measuring all four Stokes brightness parameters, is used. Imaging is achieved using a 1-m aperture conically scanning antenna. The polarimetric azimuthal signature of the ocean is known from modeling and circle flight experiments. Combining the signature with the measured brightness data from just a single flight track enables the wind direction to be determined on a pixel-by-pixel basis in the radiometer imagery