星载全极化微波散射计系统仿真与性能分析

本文对全极化微波散射计遥感海面风场的原理及其特点进行研究,建立了星载全极化微波散射计的系统仿真模型.对比了SeaWinds散射计参数下全极化与同极化的风场反演质量,结果表明全极化微波散射计在星下点以及刈幅远端的区域有良好的风场反演性能,并可提升高风速条件下的风场反演精度.最后分析了极化通道隔离度对全极化散射计系统性能的影响.     

基于笔形波束扫描雷达散射计的海洋表面流测量

为了研究利用雷达散射计进行海洋表面流直接测量的可行性,本文对传统雷达散射计系统参数进行了改进,推导了相关系数模型及去相关因素的表示形式,给出了相位误差模型,并建立了利用雷达散射计进行海洋表面流直接测量的端到端仿真模型.仿真结果表明,在风速大于5m/s的海况条件下,顺轨向和交轨向速度分量标准差可达0.1m/s以下.风速大于7m/s时,可用于海洋表面流反演的刈幅范围大于散射计刈幅宽度的40%.新型散射计的风单元传递误差无论是在低风速还是在高风速条件下均优于扇形波束扫描散射计的风单元传递误差.     

不同增益天线旋转扫描扇形波束散射计的 风场反演仿真

 本文介绍了一种星载Ku波段旋转扫描扇形波束散射计及其主要系统参数.该散射计工作在500km高度的太阳同步轨道.通过仿真比较这种散射计在不同增益天线下的风场反演能力,确定刈幅大于1000km时天线的双程增益应不小于51.5dB、距离向3dB波束宽度约为25度.最后将反演风场的质量与笔形波束的SeaWinds散射计的结果进行对比,得知这种新型的散射计有良好的风场反演能力.特别地,它能显著改善高风速条件下的风向反演精度.     

基于总变分正则化算法的散射计图像重构

目前业务化运行的星载散射计分辨率一般为25 km,在分辨率需求较高的应用中(如极地海冰监测、热带雨林监测、近岸风场研究等)受到了限制。散射计图像重构技术可以在不改变系统硬件的前提下,通过数据处理方法的改进,提高分辨率。现有的散射计图像重构方法(SIR)是基于图像处理领域中较早期的乘性代数重建技术(MART)。该文针对星载扇形旋转扫描散射计,将一种新的图像重构方法总变分正则化 (total variation regularization) 算法应用于散射计图像重构,并通过仿真实验说明,新算法可以在增强分辨率的同时减少噪声,提高重构图像的质量。     

多波段散射计系统性能的实验研究

在对多波段散射计系统及天线进行两次测试的基础上，通过对实验结果的分析，给出了系统用于目标散射特性测量时的误差因素分析及系统性能的评价。     

新型X波段散射计辐射计组合系统

为进地同地相继连续的多极化后向散射和热辐射的主被动遥感的组合测量,本文介绍了一种新型Ｘ波段散射计辐射计组合系统。该系统工作制式采用双参考数字解调辐射计与噪声散射计组合。     

非均匀植被地表散射的Monte Carlo数值模拟与实验观测

用Monte Carlo方法数值模拟电磁波在非均匀植被地表和目标的多次散射,得到随散射计空间移动观测下进而均匀植被地表的散射模拟结果,并与X波段散射计辐射计组合系统的观测试验的测量结果作了对比。     

散射辐射组合系统对造波水面的观测研究

介绍了新研制的Ｘ波段散射计组合系统。利用这一组系统进行了同时同地相继观测，得到ｖｗ，ｈｈ，ｈｖ多极化的后向散射系数σ＾０ＰＱ（ｐ，ｑ－ｖ，ｈ），ｖ和ｈ极化的辐射亮温度ＴＢＰ（ｐ＝ｖ，ｈ）。为模拟海面风场驱动起伏海面，利用室内人工造波池，在机械驱动下产生给定波谱的随机性或周期性起伏水面。用该散射计地组合系统观测多角度与多种起伏高度时的σ＾０ｐｑ－ＴＢｐ。并用双尺度随机粗糙面散射辐射理论模，烽值地模拟     

遥感、遥测、遥控

TP73 00031569新型的x波段散射计辐射计组合系统/姚传亮,金平秋,赵银龙,方振和,张南雄,章俊(上海大学)汀电子科学学刊.一2000,22(1)一137一143为进行同时同地相继连续的多极化后向散射和热辐射的主被动遥感的组合测量,文中介绍了一种新型X波段散射计辐射计组合系统.该系统工作制式采用双参考数字解调辐射计与噪声散射计组合.散射系数a“的测量不同于传统的调频连续波体制和脉冲体制,发射信号是由固态噪声源发出的微波热噪声信号,用辐射计接收机测量目标回波信号大小因此,该系统比连续波体制有更宽的频谱,而且与辐射计测量的频谱一致.测出…     

激光大气散射离轴探测建模及仿真

基于米氏散射理论,建立了波长1.064μm激光离轴散射探测模型。利用编程语言MATLAB设计了激光离轴散射探测仿真软件,该软件能够仿真计算多种大气传输条件下的散射辐射参量,并绘制相应的曲线。对激光告警散射截获半径评估和制导激光散射光特性进行了仿真计算,结果表明,该模型能够预测不同气象条件下的散射参量,为系统设计者和工程使用方提供了简便、快速的大气散射仿真工具。     

High-resolution measurements with a spaceborne pencil-beam scatterometer using combined range/Doppler discrimination techniques

Conically scanning pencil-beam scatterometer systems, such as the SeaWinds radar, constitute an important class of instruments for spaceborne climate observation. In addition to ocean winds, scatterometer data are being applied to a wide range of land and cryospheric applications. A key issue for future scatterometer missions is improved spatial resolution. Pencil-beam scatterometers to date have been real-aperture systems where only range discrimination is used, resulting in a relatively coarse resolution of approximately 25 km. In this paper, the addition of Doppler discrimination techniques is proposed to meet the need for higher resolution. The unique issues associated with the simultaneous application of range and Doppler processing to a conically scanning radar are addressed, and expressions for the theoretical measurement performance of such a system are derived. Important differences with side-looking imaging radars, which also may employ Doppler techniques, are highlighted. Conceptual design examples based on scatterometer missions of current interest are provided to illustrate this new high-resolution scatterometer approach. It is shown that spatial resolution of pencil-beam scatterometer systems can be improved by an order of magnitude by utilizing combined range/Doppler discrimination techniques, while maintaining the wide-swath and constant incidence angle needed for many geophysical measurements.     

A millimeterwave network analyzer based scatterometer

The Millimeterwave Polarimeter (MMP) is a network-analyzer-based scatterometer and reflectometer system that has been developed to characterize radar clutter at 35, 94, and 140 GHz. A Hewlett-Packard 8510A network analyzer is used in the MMP system as a signal conditioner and processor to facilitate real-time data reduction, to reduce the short time-delay leakage noise inherent in traditional FM/CW radar, and to further enhance the signal-to-noise ratio of the system through signal processing techniques. Operation of the system at millimeter wavelengths is achieved with upconversion and harmonic downconversion. The use of harmonic downconverters permits low-frequency signal connections between components of the system and allows easy reconfiguration in either scatterometer, bistatic, or reflection/transmission modes     

Radar Backscatter Measurement Accuracies Using Digital Doppler Processors in Spaceborne Scatterometers

The normalized standard deviation, Kp, of radar backscatter measurements using digital Doppler processors in spaceborne scatterometers is derived. The Kp expression for analog Doppler filter processors, such as that used in the Seasat scatterometer [7] is shown to be a special case of the derived Kp expression. A connection to Welch's power spectrum estimation results [6] is also made. Tradeoff studies in digital filter design such as hardware complexity, computational speed, and system performance can be performed based on this Kp expression. We briefly discuss a current application in the design of the NASA scatterometer (NSCAT) to be flown in 1990. This derivation should be useful for system design and analysis of other radar remotesensing instruments.     

Vegetation studies of the Amazon basin using enhanced resolutionSeasat scatterometer data

The Seasat-A scatterometer (SASS) was designed to measure the near-surface wind field over the ocean by inferring the wind from measurements of the surface radar backscatter. While backscatter measurements were also made over land, they have been primarily used for the calibration of the instrument. This has been due in part to the low resolution of the scatterometer measurements (nominally 50 km). In a separate paper the present authors introduced a new method for generating enhanced resolution radar measurements of the Earth's surface using spaceborne scatterometry. In the present paper, the method is used with SASS data to study vegetation classification over the extended Amazon basin using the resulting medium-scale radar images. The remarkable correlation between the Ku-band radar images and vegetation formations is explored, and the results of several successful experiments to classify the general vegetation classes using the image data are presented. The results demonstrate the utility of medium-scale radar imagery in the study of tropical vegetation and permit utilization of both historic and contemporary scatterometer data for studies of global change. Because the scatterometer provides frequent, wide-area coverage at a variety of incidence angles, it can supplement higher resolution instruments which often have narrow swaths with limited coverage and incidence angle diversity     

Estimation of sea-surface winds using backscatter cross-sectionmeasurements from airborne research weather radar

A technique is presented for estimation of sea-surface winds using backscatter cross-section measurements from an airborne research weather radar. The technique is based on an empirical relation developed for use with satellite-borne microwave scatterometers which derives sea-surface winds from radar backscatter cross-section measurements. Unlike a scatterometer, the airborne research weather radar is a Doppler radar designed to measure atmospheric storm structure and kinematics. Designed to scan the atmosphere, the radar also scans the ocean surface over a wide range of azimuths, with the incidence angle and polarization angle changing continuously during each scan. The new sea-surface wind estimation technique accounts for these variations in incidence angle and polarization and derives the atmospheric surface winds. The technique works well over the range of wind conditions over which the wind speed-backscatter cross-section relation holds, about 2-20 m/s. The problems likely to be encountered with this new technique are evaluated and it is concluded that most problems are those which are endemic to any microwave scatterometer wind estimation technique. The new technique will enable using the research weather radar to provide measurements which would otherwise require use of a dedicated scatterometer     

Calibration of spaceborne scatterometers using tropical rainforests

Wind scatterometers are radar systems designed specifically to measure the normalized radar backscatter coefficient (σ°) of the ocean's surface in order to determine the near-surface wind vector. Postlaunch calibration of a wind scatterometer can be performed with an extended-area natural target such as the Amazon tropical rain forest. Rain forests exhibit a remarkably high degree of homogeneity in their radar response over a very large area though some spatial and temporal variability exist. The authors present a simple technique for calibrating scatterometer data using tropical rain forests, Using a polynomial model for the rolloff of σ° with incidence angle, the technique determines gain corrections to ensure consistency between different antennas and processing channels. Corrections for the time varying instrument gain are made consistent with a seasonally fixed rain forest response; however, without ground stations or aircraft flights, it is difficult to uniquely distinguish between seasonal variations in the rain forest and slow variations of the system gain. Applying the corrections, the intrinsic variability of the σ° of the rain forest is estimated to be ±0.15 dB, which is the limit of the accuracy of calibration using the rain forest. The technique is illustrated with Seasat scatterometer (SASS) data and applied to ERS-1 Active Microwave Instrument scatterometer (Escat) data. Gain corrections of up to several tenths of a decibel are estimated for SASS. Corrections for Escat data are found to be very small, suggesting that Escat data is well calibrated     

相干雷达高度表大地回波去相关研究与实验

由于非刚体目标自身的变化或者刚体目标与雷达之间的距离、视角发生变化都会产生大地回波去相关现象.文中针对上述现象建立了大地回波的几何与幅度起伏模型,对机载相干雷达高度表回波特性进行了仿真研究.文中还利用S波段相干脉冲散射计开展了大地回波测量实验,对回波数据进行了相干处理,并对仿真结果进行了实验验证.仿真与实验的结果表明:大地回波的去相关损失取决于地面粗糙度以及载机在一个脉冲重复周期内移动的距离.     

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.     

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