A New Spectral Estimate for the SAR Image of the Ocean

We present a consistent theory of synthetic aperture radar (SAR) imaging of the ocean surface. Based on the composite model of microwave backscattering, the theory describes both the image itself and speckle noise, which is the factor preventing the interpretation of SAR imagery of the ocean. We propose a new spectral estimate, which, from the statistical viewpoint, eliminates completely speckle noise in the SAR image spectrum and does not deteriorate the SAR resolution. The new technique for estimating the spectrum is tested using the SAR data of the European satellites ERS-1 and ERS-2.     

Accuracy Estimate for Determination of the Near-Surface Wind Velocity Using the SAR Ocean Image Spectrum

Numerical modeling of the SAR image of wind waves propagating azimuthally is performed for various wind velocities. It is shown that if the wind is relatively weak (up to 10 m/s), then the position of the image-spectrum maximum is a fairly sensitive parameter, such that the accuracy of the respective wind-velocity measurement technique for these wind velocities should be 1 m/s or less for a high spatial resolution. Under conditions of stronger wind, the sensitivity decreases; however, more definite results for the stronger-wind domain can be obtained only experimentally. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 6, pp. 472–477, June 2005.     

一种SAR成像快速算法及优化实现

针对实时SAR成像处理中相关运算量大的特点,提出了新的频域分解快速算法和优化设计方法.根据参数优化准则,选择合适的填零个数和DFT点数分解方式,分析出利用频域分解和频域分段两种算法,可以大大减少相关运算中FFT变换的运算量.在不同情况下,详细分析了多种算法的速度性能和适用性.在并行多处理器上利用此算法,降低了SAR实时成像的运算量和成像延迟,显著提高了SAR实时成像的处理速度.     

一维粗糙地表面下方埋藏目标SAR成像

提出一种快速实现一维粗糙地表面下方埋藏金属目标的成像算法.用层内波传播算法结合谱加速的前后向迭代算法(PILE+FB-SA)计算一维粗糙面下方埋藏金属目标的后向散射;用得到的后向散射数据结合后向投影算法实现二维SAR(synthetic aperture radar)成像,研究窗函数的选取,讨论目标位置及尺寸大小变化的影响.用具有高斯谱的粗糙面模拟实际地表面,并采用锥形波入射以减小人为截断粗糙面引起的边缘效应.由于散射数据由快速数值算法得到,该算法不受地面和目标参数限制,可以实现任意粗糙地表面和复杂目标成像,对地下目标探测具有重要的应用价值.     

基于小波的多极化机载合成孔径雷达海面风向反演

为了实现从合成孔径雷达(SAR)图像本身提取高精度的海面风向信息, 提高SAR海面风场反演精度,研究了多极化机载SAR海面风向反演技术, 借助小波分析相对傅里叶分析和局部梯度更精细的时-频分析能力, 将二维连续小波变换与快速傅里叶变换(FFT)相结合,提出一种新的机载SAR海面风向反演方法. 为验证反演方法的有效性,通过海上同步飞行试验获取多极化机载SAR数据及同步调查船实测风向数据,用于反演试验的数据比对.采用本文提出的方法, 利用多种小波基对机载C波段SAR的同极化和交叉极化数据进行风向反演, 将反演结果与美国国家环境预报中心再分析资料以及调查船实测风向进行比对. 结果表明,本文提出的基于小波分析的海面风向反演方法适用于机载SAR探测数据, 反演精度优于二维FFT法和局部梯度方法;小波基的选择对反演结果影响较大, Mexican-Hat小波基是机载SAR海面风向反演的最优小波基, 且同极化与交叉极化机载SAR数据均可用于海面风向的反演.     

毫米波步进频连续波SAR成像系统研究

研究了一种基于毫米波的步进频连续波合成孔径雷达成像系统。基于算法研究,搭建了成像硬件及软件系统,实现信号扫描及回波信号的采集与处理。处理后的信号通过成像算法计算,获得目标物体的三维图像数据。实验测试了系统x、y、z方向的分辨率,测试结果表明系统x方向分辨率在8～9 mm,y方向分辨率为12 mm,z方向分辨率为40 mm左右。研究了系统的最佳成像距离,实验发现,当目标物体在距离收发天线5～16 cm范围时,均可对目标清晰成像且仅有很小的背景噪声。在人体安检的应用上,检测了五种常见面料的穿透效果。实验结果表明,在正常衣物厚度下,系统能有效地穿透面料并对隐藏物体清晰成像。     

西太平洋蒸发波导的时空统计规律研究

海洋蒸发波导自然现象对近海面电磁波的传播有重要影响,获取大面积海域蒸发波导的长时间统计分布规律,对于海上雷达、通信、制导等电磁系统的设计与应用,具有重要意义.针对现有单点局部观测方法的缺点,建立了基于美国环境预报中心再分析数据的大面积海域蒸发波导统计特性计算方法,利用太平洋气象浮标数据、北部湾海岛气象观测数据对分析方法的正确性进行了验证.利用该分析方法和最近18年的美国环境预报中心再分析数据,重点研究了西太平洋蒸发波导的统计规律,获得了蒸发波导高度在不同海域、不同月份的分布特性,建立了空间分辨率约为18 关键词： 蒸发波导 再分析数据 电磁波 统计特性     

Multi-sensors SAR system for real-time dosimetry assessment

A multi-sensor test-bench for determining the SAR (specific absorption rate) due to wireless devices emitting in equivalent human tissues is presented. Real-time SAR assessment is proposed considering a spatially distributed multiprobe test-bench. In comparison with a multi-axial robot SAR system, the proposed one does not require any displacement, thus reducing drastically acquisition time, once parallel data acquisition and interpolation techniques are employed for accelerating measurements.     

干涉型计算层析成像光谱仪的图像重建

针对干涉型计算层析成像光谱仪(CTII)提出了一种光谱图像数据立方体的重建方法。干涉型计算层析成像光谱仪是一种将空间调制傅里叶变换成像光谱仪(FTIS)的原理与计算层析成像光谱仪(CTIS)的原理相结合的一种新型成像光谱仪,具有高通量、高光谱分辨力以及高空间分辨力的特点。分析和讨论了干涉型计算层析成像光谱仪的工作原理以及获取图像的特征,介绍了光谱图像数据立方体的重建方法。根据多角度投影数据的特点提出采用卷积反投影计算层析成像图像重建算法,给出了图像重建步骤以及相应的数学表达式。对D65光源照明条件下的396×396像素目标进行了仿真实验,投影角度为0~180°,步长为0.5°,列出了仿真实验部分结果。实验结果验证了干涉型计算层析成像光谱仪及其图像重建算法的可行性。     

Self-organized Criticality Model for Ocean Internal Waves

In this paper, we present a simple spring-block model for ocean internal waves based on the self-organized criticality （SOC）. The oscillations of the water blocks in the model display power-law behavior with an exponent of -2 in the frequency domain, which is similar to the current and sea water temperature spectra in the actual ocean and the universal Garrett and Munk deep ocean internal wave model [Geophysical Fluid Dynamics 2 （1972） 225; J. Geophys. Res. 80 （1975） 291]. The influence of the ratio of the driving force to the spring coefficient to SOC behaviors in the model is also discussed.     

Mechanisms for similarity based cooperation

Cooperation based on similarity has been discussed since Richard Dawkins introduced the term “green beard” effect. In these models, individuals cooperate based on an aribtrary signal (or tag) such as the famous green beard. Here, two different models for such tag based cooperation are analysed. As neutral drift is important in both models, a finite population framework is applied. The first model, which we term “cooperative tags” considers a situation in which groups of cooperators are formed by some joint signal. Defectors adopting the signal and exploiting the group can lead to a breakdown of cooperation. In this case, conditions are derived under which the average abundance of the more cooperative strategy exceeds 50%. The second model considers a situation in which individuals start defecting towards others that are not similar to them. This situation is termed “defective tags”. It is shown that in this case, individuals using tags to cooperate exclusively with their own kind dominate over unconditional cooperators.     

Evaluating the efficiency of TT-OSL SAR protocols

Optically Stimulated Luminescence (OSL) dating based on the fast component is now widely used to establish chronologies of sedimentary deposits. Since this component saturates at a relatively low dose, the method is limited to the dating of Late Pleistocene quartz samples. Consequently, dating events beyond this limit is a key challenge. In this context the use of the TT-OSL signal which exhibits a high doses saturation level offers the potential to extend the age range of the method. Since the promising study of Wang et al. (2006b), in which a 780 ka age validated by palaeomagnetism data was reported for a Chinese loess sample, several studies focused on establishing a SAR TT-OSL dating protocol. They suggested applying different kinds of heat treatment at the end of a SAR cycle, as well as two normalisation procedures. The aim of this study was to test the reliability of these protocols for a loess-like Middle Pleistocene sample for which the expected De is known approximatively. We tested four published SAR protocols by implementing the dose recovery tests on artificially bleached quartz aliquots. The results obtained showed a systematic overestimation of the recovered doses and revealed high sensitivity changes between the first (natural) and the following cycles. It is believed that this behaviour is a consequence of the thermal treatment applied at the end of each SAR cycle which is necessary to empty the hard-to-bleach TT-OSL traps. Neither OSL nor TT-OSL signal test dose responses proved suitable to correct this sensitivity change.     

逆合成孔径成像激光雷达实包络成像算法

逆合成孔径激光成像雷达受激光调制技术以及回波相位信息易受大气湍流破坏的限制,采用常规的相位相干积累类方法得到目标二维高分辨图像很困难.针对这一情况,提出了一种基于逆Radon变换的实包络成像算法.利用回波距离脉冲压缩后的实包络信息,实现方位向的非相干积累,最终得到二维高分辨图像.通过该算法,成像系统可以使用非相干激光信号,在脉冲重复频率较低且存在大气湍流的情况下,也可以获得高质量的成像结果.仿真实验验证了此算法的有效性和优越性.     

逆合成孔径成像激光雷达实包络成像算法

逆合成孔径激光成像雷达受激光调制技术以及回波相位信息易受大气湍流破坏的限制,采用常规的相位相干积累类方法得到目标二维高分辨图像很困难.针对这一情况,提出了一种基于逆Radon变换的实包络成像算法.利用回波距离脉冲压缩后的实包络信息,实现方位向的非相干积累,最终得到二维高分辨图像.通过该算法,成像系统可以使用非相干激光信号,在脉冲重复频率较低且存在大气湍流的情况下,也可以获得高质量的成像结果.仿真实验验证了此算法的有效性和优越性.     

New polarimetric signal subspace detectors for SAR processors

Our studies aim at detecting targets embedded in a complex environment for radar applications. This article deals with new polarimetric SAR (synthetic aperture radar) processors based on subspace detectors. These algorithms use models of targets including physical and polarimetric properties of their scattering on the contrary to the isotropic point model that is commonly used. These processors are implemented by computing the corresponding subspaces that contain the relevant responses of the target. We choose for application the detection of targets under forest foliage. The obtained results both on simulated data of realistic targets and real data show the interest of these new processors.     

合成孔径激光成像雷达的二维傅里叶变换成像算法

提出了合成孔径激光成像雷达(SAIL)的二维傅里叶变换成像算法,即对回波信号进行顺轨向相位二次项共轭补偿后直接实施二维傅里叶变换。归纳了啁啾光源侧视SAIL,平移二次项波面直视SAIL和偏转平面波面直视SAIL的数据收集方程,采用连续变量和函数说明了算法的成像过程,并分析了矩形和圆形天线孔径下的成像分辨率,最后给出了离散傅里叶变换的表达形式。算法中交轨向和顺轨向的时间域数据均直接变换到频率域成像,给出了圆形孔径天线SAIL的随交轨向变化的顺轨向成像分辨率的解析解。     

红外热像仪SiTF的测试研究

信号传递函数(SiTF)是评价红外热像仪性能的最基本且最关键的技术指标之一，它是响应度函数的线性部分，从响应度函数测试曲线中可得到待测系统增益、线性度、动态范围和饱和度的信息。采用高精度的双黑体反射靶标评估系统对CEDIT IIA型热像仪的SiTF进行了测试分析。该系统保证了背景辐射的均匀稳定，且受环境温度变化的影响极小，从而大大提高了测量的准确性和可靠性。最后给出了测试SiTF时出现波动的多种可能原因。     

Laryngeal Mechanisms During Human 4-kHz Vocalization Studied With CT, Videostroboscopy, and Color Doppler Imaging

The objective of this study was to investigate the underlying laryngeal mechanisms during the specific human 4-kHz vocalization. The laryngeal configuration during this vocalization was measured using high-resolution computerized tomographic scan and videostrobolaryngoscopy. The color Doppler imaging (CDI) of medical ultrasound was used to detect the vibrations of glottal and supraglottal mucosa. During the 4-kHz vocalization, the ventricular folds were adducted in the shape of a bimodal chink and the vocal folds were shaped as a "V" with an opening at the posterior glottis. In the coronal view, the laryngeal ventricles had collapsed and a divergent shaped conduit was observed at the posterior portion of the larynx. The surface mucosa vibration detected by CDI was noted over the bilateral ventricular folds and aryepiglottic folds. The vibration displacement was estimated to be on the order of 0.1mm. This vibration amplitude was too small to be detected in videostrobolaryngoscopy. The laryngeal configuration and CDI data suggested a diffuser jet with periodic vorticity bursts in the larynx producing 4 kHz voice.