基于稀疏采样与级联字典的微波辐射图像重构方法*

针对微波辐射测量成像系统在一次观测中所采集的数据量大,基于奈奎斯特采样的常规,微波辐射成像方法难以实现高分辨率要求。本文在挖掘微波辐射图像多结构信息可压缩的基础上,利用随机观测矩阵对微波辐射图像进行线性压缩投影,减少数据采集量,降低系统的复杂性。考虑微波辐射图像具有多结构形式,采用单一的正交基难以稀疏表示复杂场景的微波辐射图像,利用全变差分和小波的级联字典对微波辐射图像进行稀疏表示,然后用OMP 算法重构微波辐射图像。仿真实验结果表明:级联字典重构微波辐射图像的性能优于单一正交基。     

综合孔径微波辐射计成像观测能力

对综合孔径微波辐射计成像观测原理进行了阐述,分析了综合孔径微波辐射计的灵敏度、积分时间、天线波束宽度、目标亮温、背景噪声温度、系统工作频率和目标等效截面等因素与系统作用距离的关系,对系统的目标观测能力进行仿真验证,探讨了阵列通道不一致等误差的补偿方法。研究成果将有助于综合孔径微波辐射计的实用化推进。     

微波关联成像研究进展及展望（特邀）

微波关联成像起源于光学强度关联成像,通过对电磁波的调控形成空变和时变的辐射模式,突破天线孔径对成像分辨率的限制,具有前视、凝视、快拍成像等优势,在重点区域凝视观测、无人系统自主感知、安检安防等领域具有广阔的应用前景。文中简述了微波关联成像的技术起源,从成像原理、成像方法、成像系统等三个方面,总结了微波关联成像的研究现状与主要进展。通过对成像原理的剖析,阐明关联成像的基本条件与成像分辨率的影响因素;通过对成像方法的梳理,分析微波关联成像与光学关联成像以及传统微波成像方法之间的区别与联系;通过对成像系统的介绍,比较随机辐射、波前调制、孔径编码等多种成像体制的特点与差异,厘清技术发展脉络。最后,总结并展望了微波关联成像的未来发展趋势。     

用于医学的连续波太赫相机

几个德国研究组合作，研制出以连续波太赫辐射为基础的第一台太赫成像光谱仪。其中三个组在德国不伦瑞克，第四小组在马布格。设计的成像系统廉价、紧凑，主要用于生物学和医学的成像。太赫兹(THz)频率处在远红外区，位于光学光谱和现代微波电信频率之间，是尚未开发的应用领域，具有巨大发展潜力。其中之一是成像。最近研究表明，太赫成像可获得比微波成像更好的分辨率。开发这类系统的一个问题是在几百吉赫和几太赫之间的光谱区很难存取。最近太赫成像已用脉冲辐射演示。用飞秒激光脉冲选通偏压光导偶极子天线产生太赫辐射。选通使短电流…     

一种微波暗室目标成像技术的研究与实现

研究了时域超宽带紧缩场微波暗室内雷达目标成像的机理,这是一种雷达不动、目标转动的逆合成孔径成像方式。首先得到某辐射点在各角度下的辐射功率,将这些功率相加得该点的总辐射强度。每个分辨单元视为一个辐射点,求其功率并归一化,即得成像灰度图。提供了测量系统的结构框图,分析了成像算法,推导了数据处理公式。在此基础上,编制开发了成像测量软件并进行了微波成像实验。最后,提供了典型目标导体球的成像结果。     

单脉冲微波功率与能量的量测

讨论了应用电磁波的辐射压力在空间测量微波功率，特别是单次脉冲高功率微波的峰值功率和能量的方法。设计了一个测量空间辐射压力的悬挂系统扭秤。对于该悬挂系统进行了系统模拟，给出了测量微波辐射压力的定性实验结果。证明该方法是可行的。     

基于混合稀疏基字典学习的微波辐射图像重构方法

目前的微波辐射测量成像系统在一次观测中所采集的数据量大,基于奈奎斯特空间采样及常规微波辐射图像重构方法难以实现高分辨率要求。该文针对微波辐射干涉测量在频域中进行,采用傅里叶最优随机抽取的超稀疏干涉测量(低于奈奎斯特采样)对微波辐射图像进行线性压缩投影,降低数据采样。考虑微波辐射图像在总体差分域和小波中都具有可压缩特性,提出总体差分和小波混合正交基的K-SVD字典学习微波辐射图像重构模型,利用Bregman和交替迭代算法求解该模型,重构线性压缩投影信息从而获得微波辐射图像。仿真实验表明,该文提出的算法在微波辐射图像重构效果、噪声稳定性上优于DLMRI算法和GradDLRec算法。     

红外图像特征分析与模拟

分析了景物实际存在的红外辐射特征，结合红外热成像系统的性能特点，把热像仪与景物红外辐射的相互用归纳时间，空间和空时转换关系，在红外热成像实验结果的支持下，对多种复杂条件下的红外热成像结果进行了理论与数值分析，根据红外图像特征分析结果提出了可以真实模拟３～５μｍ和８～１４μｍ波段红外辐射的双波段动态红外图像模拟技术。     

基于先验信息的综合孔径辐射计误差校正方法

误差会严重影响综合孔径微波辐射计的成像性能,需要进行校正.但是,随着系统工作频率的提高和阵列尺寸的扩大,校正难度越来越大.文中提出一种基于先验信息的综合孔径微波辐射计误差校正方法.该校正方法包括一个基于先验信息的校正矩阵以及一种基于先验信息的CLEAN算法.首先,该校正方法将含有误差的系统响应作为先验信息构造校正矩阵,并校正得到初步的反演图像;然后,利用上述先验信息估计系统的阵列因子并代入基于先验信息的CLEAN算法,校正图像中剩余的误差.仿真和实验结果表明该校正方法能有效提高综合孔径微波辐射计的成像质量.该校正方法可以在图像反演过程中全面校正综合孔径微波辐射计的误差,降低对校正系统的硬件性能要求,适用于大阵列毫米波综合孔径微波辐射计的校正误差.     

遥感、遥测、遥控

TP751·95061325枷.波段二维扫描辐射成像的研究/郭伟,,张祖荫,刘伟,卢军(华中理工大学)11华中理工大学学报.一1995,23(7)一35一38 根据地物及目标的微波辐射特性,叙述了微波辐射图像的成像机理,系统结构,图像的特征、处理及判读的方法.成像实验结果表明:在场景的微波辐射图像上,金属目标、水面、.树木、草地和道路的特征十分明显.图5表1参3(金)理造成很大困难,针对这些特点文中叙述了从影像中提取噪声谱后利用方向滤波法消去条带噪声.墓于自动识别理论进行分类增强,采用相关匹配和加权平滑法进行不同时期卫星影像镶嵌等几项特殊处理技术.…     

Airborne imaging radiometer scan simulation

An imaging radiometer scan simulation program is developed for comparing the performance of different scan patterns and process behavior under varying circumstances. The program gives the radiometer's antenna beam the desired scan motion over an artificial target scene, computes the antenna radiometric temperature as the convolution of the antenna pattern with the scene brightness temperature deviation, computes a moving average of the antenna output, and records the data values as well as the corresponding coordinates at the sampling moments. The simulation indicated that a helicopter-borne imager needs at least passive attitude stabilization. In addition, the state-of-the-art sampling rate was found to be too slow, if the sampling period is set equal to the integration time. A detailed study revealed the achievable spatial resolution (line pairs/length unit-definition) to be 1.0-1.2×footprint dimensions, but the integration and sampling periods should be as short as 0.2-0.4×footprint dimensions     

GEOSAT Follow-On Water Vapor Radiometer: Performance With a Shared Active/Passive Antenna

The GEOSAT Follow-On mission marks the first time that an Earth-orbiting microwave radiometer and radar have shared the same antenna. The antenna design must simultaneously accommodate the radar's high-gain requirement and the high beam efficiency needed by the radiometer. Guaranteeing sufficiently high isolation between the radar transmitter and the radiometer receivers is also a critical part of the antenna design. The radiometer receiver includes a transmitter blanking circuit to further mitigate possible radar interference. Preflight and on-orbit tests of the antenna and radiometer receivers and an evaluation of end-to-end radiometric accuracy are presented. Together, they demonstrate that the shared-antenna approach can be implemented without compromising radiometric performance     

数字增益补偿及实时定标微波辐射计

微波辐射计的长期稳定性,是影响最小可检测信号的主要因素。研究出数字增益补偿与实时定标两种新型微波辐射计。能完全消除系统增益波动的影响。有极好的长期稳定性。实时定标型还能消除系统噪声的波动,完成实时定标。在０．６ｓ时间常数下最小可检测信号分别达到０．１３和０．１９Ｋ,达到国内外先进指标。在实际中已得到应用。     

3mm波段辐射成像研究

在研制3mm D icke辐射计的基础上,设计出基于PC-MCU主从控制模式的成像系统.针对运动平台成像系统提高灵敏度与空间分辨率的矛盾,采用软积分调节系统的积分时间,给出了软硬积分级联系统的积分公式,并采用了一种复合形态滤波器改善辐射图像分辨率的方法.实验结果表明:3mm辐射图像明显优于8mm辐射图像的空间分辨率,形态学的处理方法可有效地去除图像的噪声,验证了软积分在一定程度上可替代硬积分的功能.3mmD icke辐射计的指标为中心频率94GHz,灵敏度0.2K,线性度0.999,系统带宽2GHz,卡赛格伦天线3dB波束宽度为0.5°.     

基于滤波反投影算法的自旋式综合孔径辐射计分辨率与灵敏度分析

针对自旋式稀疏阵列综合孔径微波辐射计近似于极坐标的采样方式下成像算法复杂、系统参数估计困难等问题,该文提出一种基于滤波反投影算法的系统参数估计方法。该方法通过对极坐标下狄拉克采样梳子函数进行1维傅里叶-汉克尔变换得到系统的点扩散函数,并根据点扩散函数主副瓣分解,重点分析了径向与角度方向采样间隔对无混叠视场范围的影响以及主瓣宽度对应的分辨率。该文同时利用滤波反投影算法推导了自旋式稀疏阵列辐射灵敏度的估计方法。数值仿真与实测点源响应函数的一致性表明了该模型的精确性。     

Programmable sweep radiometer system as a new tool for non-invasive thermometry.

A new microwave radiometer system consisting of a frequency sweep-type radiometer and an ultra wideband antenna has been developed. A computer-controlled radiometer system covers the input frequency range from 0.5 GHz to 8 GHz. It can be used not only as a multispectral radiometer system whose frequencies can be chosen freely, but also as a frequency sweep-type radiometer system whose frequency is continuously swept during measurement. When an antenna is attached to a forearm, the sensitivity of the radiometer system exceeds 0.09 degree C when the integration time is 3 sec and IF bandwidth is 500 MHz. The new microwave radiometer system may be utilized for non-invasive thermometry of the human body.     

TWO NEW TYPES OF MICROWAVE RADIOMETER: A COMPUTER GAIN COMPENSATIVE DESIGN AND A REAL-TIME CALIBRATED DESIGN

Long term stability is the main factor that influences the minimum detectable signal of microwave radiometers. Two new types of microwave radiometer were studied: a computer gain compensative microwave radiometer and a real-time calibrated microwave radiometer. The long term stability of both designs was optimal because they were insensitive to system gain fluctuations. The continuous calibrated microwave radiometer was also insensitive to system noise fluctuations. The minimum detectable signals were 0.13 and 0.19K respectively under an integration time of 0.6s.     

Experimental Research on Optimal Millimeter Wave Radiometric Images

Widely used in remote sensing and guidance, radiometer is a typical passive detection system. However, it is an important problem to improve the millimeter wave radiometric imaging resolution. On basis of discussing imaging theory of radiometer, this paper presents the way to get optimal radiometric images by experimental research. The experimental result shows the satisfying images can be obtained by the matching of the parameters.     

Design of 8mm-band Aperture Synthetic Radiometer and Imaging Experiment

An aperture synthetic radiometer (ASR) based on interferometric technology is a new type of passive microwave imaging instrument, which has high spatial resolution. Restricted by devices performance and operating wavelength, however, the system design is difficult at MMW band. In this paper, an 8mm-band aperture synthetic radiometric imaging system based on minimum-redundancy linear array is described, the performance specification of the instrument is analyzed. The preliminary imaging experiment result shows that the system has good passive MMW imaging (PMMWI) performance, indicating a bright outlook for the development of this technique in the future.     

Modeling the visibility of breast malignancy by a microwave radiometer

A breast tumor is visible by a passive microwave radiometer if it changes the radiometric output of a healthy breast to an extent that overcomes the radiometric resolution for the given sensing antenna and integration time. We modeled breast temperature by the standard Pennes equation using thermal parameters found in the literature for normal and cancerous breast tissue. An apparent thermal volume and its dependence on blood perfusion have been estimated. The radiometric weighting function has been evaluated as a function of the size of a contacting antenna modeled as an aperture antenna. For comparison with the radiometric resolution, the difference signal between the outputs in the presence of a lesion and in its absence has been evaluated for different tumor sizes and depths. The results of the numerical analysis show that this difference signal depends on the average over-temperature in the lesion times the heating efficiency, given by the fraction of power delivered to the tumor when the antenna radiates onto the breast in active modality. A tumor of 6 mm (10 mm) diameter is visible by a 0.1 K radiometer and a 3 cm aperture antenna when it is not deeper than 1.2 cm (2.8 cm) under the assumption of ideal radiometer and antenna.