基于逆Radon变换的圆迹SAR三维成像算法

随着合成孔径雷达(synthetic aperture radar,SAR)的应用需求不断提高,出现了圆迹SAR的成像模式,解决传统直线轨迹SAR只能获取二维斜距图像的问题,在地形测绘、建筑物提取、灾害评估等领域具有较高应用潜力。现有的圆迹SAR三维成像算法还存在计算量大、实现复杂等问题,通过对圆迹SAR模型的斜距几何分析,结合回波信号模型设计波数域补偿函数,将距离压缩曲线矫正为基线为零的正弦曲线;结合逆Radon变换,实现对目标的正弦曲线的二维聚焦;通过逐高度平面二维成像结果的堆叠,实现目标的三维成像。通过仿真分析了所提算法的成像质量,验证了所提算法三维成像的有效性。

A new calibration method for radon detector in seismic systems

Radon observation is an important measurement item of seismic precursor network observation.The radon detector calibration is a key technical link for ensuring radon observation accuracy.At present,the radon detector calibration in seismic systems in China is faced with a series of bottleneck problems,such as aging and scrap,acquisition difficulties,high supervision costs,and transportation limitations of radon sources.As a result,a large number of radon detectors cannot be accurately calibrated regularly,seriously affecting the accuracy and reliability of radon observation data in China.To solve this problem,a new calibration method for radon detectors was established.The advantage of this method is that the dangerous radioactive substance,i.e.,the radon source,can be avoided,but only“standard instruments”and water samples with certain dissolved radon concentrations can be used to realize radon detector calibration.This method avoids the risk of radioactive leakage and solves the current widespread difficulties and bottleneck of radon detector calibration in seismic systems in China.The comparison experiment with the traditional calibration method shows that the error of the calibration coefficient obtained by the new method is less than 5%compared with that by the traditional method,which meets the requirements of seismic observation systems,confirming the reliability of the new method.This new method can completely replace the traditional calibration method of using a radon source in seismic systems.

Numerical Simulation on Radon Retardation Behavior of Covering Floats in Radon-Containing Water

Objective This study aimed to efficiently reduce the release of radon from water bodies to protect the environment.Methods Based on the sizes of the experimental setup and modular float,computational fluid dynamics(CFD)was used to assess the impact of the area coverage rate,immersion depth,diffusion coefficient,and radon transfer velocity at the gas–liquid interface on radon migration and exhalation of radon-containing water.Based on the numerical simulation results,an estimation model for the radon retardation rate was constructed.The effectiveness of the CFD simulation was evaluated by comparing the experimental and simulated variation values of the radon retardation rate with the coverage area rates.Results The effect of radon transfer velocity on radon retardation in water bodies was minor and insignificant according to the appropriate value;therefore,an estimation model of the radon retardation rate of the coverage of a radon-containing water body was constructed using the synergistic impacts of three factors:area coverage rate,immersion depth,and diffusion coefficient.The deviation between the experimental and simulated results was<4.3%.Conclusion Based on the numerical simulation conditions,an estimation model of the radon retardation rate of covering floats in water bodies under the synergistic effect of multiple factors was obtained,which provides a reference for designing covering floats for radon retardation in radoncontaining water.

融合Radon变换的孔边裂纹Lamb波定位成像研究

基于不同模态Lamb波与孔边裂纹相互作用的基本原理,聚焦不同模态Lamb波波包飞行时间精确检测问题,以各向同性板中的孔边裂纹为研究对象,开展了融合Radon变换的孔边裂纹Lamb波定位成像研究。首先,使用宽频chirp信号激励稀疏传感器阵列产生Lamb波,并采集通孔散射信号作为基线信号,采集孔边裂纹散射信号作为缺陷信号。其次,对chirp响应信号进行滤波处理,优化选取窄带单音频脉冲响应信号的中心频率和调制周期数。然后,对基线单音频脉冲响应信号进行Radon变换,得到优化后的群速度和偏移时间,并计算出Lamb波波包飞行时间。最后,使用椭圆定位成像算法对孔边裂纹进行定位成像,并将成像结果与名义群速度法的结果进行对比。结果表明,使用Radon变换可以准确获取Lamb波波包飞行时间,提升了不同模态Lamb波对孔边裂纹缺陷的检测能力。

曲率放大的λ-f域高分辨率抛物Radon变换多次波压制方法

在实际数据处理中抛物Radon变换是多次波压制的一种常用手段,然而,常规Radon变换方法难以有效压制那些与一次波曲率差异较小的多次波,本文给出了曲率放大的多次波压制方法来改善多次波的压制效果。通过研究影响同相轴的曲率的参数,发现压缩炮检距或增大时差能够放大多次波和一次波曲率差异,加大一次波和多次波在Radon域的分离程度,从而提高了多次波的压制能力。为进一步提高Radon变换的计算效率和精度,采用λ-f域高分辨率抛物Radon变换,通过引入新变量λ消除了常规Radon变换算子对频率的依赖性,由于变换算子和它的逆只需要计算一次,因此显著提高了计算效率。通过理论模型和实际资料的处理表明,该方法能够较好地压制表层多次波,对于那些与一次波存在一定曲率差异的层间多次波,也具备一定的压制能力。

基于L_(1/2)正则化的抛物线Radon变换多次波压制方法

在地震数据处理中,多次波的存在会对地震数据成像和地震资料解释带来影响,如何有效地压制多次波干扰是地震勘探中的重要问题。抛物线Radon变换因其高效的特点被广泛应用于多次波压制中,但在野外地震数据采集时,炮检距的有限性会导致变换域中的能量扩散,产生假象,使多次波压制达不到理想的效果。针对此问题,提出一种基于L_(1/2)正则化的稀疏反演高分辨抛物线Radon变换,并应用广义迭代收缩算法(generalized iterated shrinkage algorithm,GISA)进行求解。研究结果表明,L_(1/2)正则化有很强的稀疏约束能力,能提高解的稀疏度,改进信噪分离的效果。与最小二乘反演和基于L_(1)正则化的稀疏反演相比,基于L_(1/2)正则化的稀疏反演高分辨抛物线Radon变换能更有效地压制多次波,并确保了重构数据与原始数据的一致性。

正交匹配追踪优化稀疏频散Radon变换多模式导波分离方法

原始频散Radon变换(DRT)方法中的有限孔径效应以及算子非正交性影响了DRT导波信号参数提取的精度,因此提出了一种稀疏频散Radon变换方法以实现更精确的导波混叠模式分离和参数估计。该方法基于导波信号的参数域稀疏性,引入正交匹配追踪算法构造代价函数,经多次迭代在频散Radon域中获得稀疏能量谱,可精确分离阵列导波信号中的混叠模式并去噪。对不同信噪比下各模式仿真信号,稀疏DRT方法的信号重建误差较原始频散Radon变换方法下降51.1%。仿真和实验验证了所提算法在导波模式参数提取和混合模式分离方面的可靠性。

水下运动平台的广义Radon变换目标参数估计方法

针对传统目标运动分析算法受静止单平台可观测性限制的问题,本文提出了一种基于广义Radon变换的水下运动平台目标参数估计方法。在观测平台自身的运动参数已知的假设下,推导了目标方位与各运动参数的数学关系,在此基础上通过对平台声呐测得的目标时间方位历程进行广义Radon变换,依次得到目标的航向角、速度以及目标相对于探测平台的初距,最终实现目标运动轨迹的解算。利用矢量阵的仿真数据对方法的可行性进行了分析验证,结果表明:作为一种批处理类方法,该方法无需进行迭代运算,易于实现,在较低信噪比条件下仍具有很好的估计精度和鲁棒性。

Radon变换频变自适应多次波压制方法

Radon变换是常用多次波压制方法之一,然而有限、离散的采样空间导致一次波和多次波在Radon域混叠,并且混叠程度随频率降低愈加严重.高分辨率Radon变换可以改善一次波和多次波分离效果,但分辨率的提高会降低保幅性,导致多次波残留或一次波损伤.为此,本文在最小二乘反演基础上,提出一种随混叠程度自适应分离多次波的频变滤波方法.根据Radon变换褶积模型,分析一次波和多次波频变混叠机制;建立随频率调整的修正柯西函数混叠模型;依据一次波和多次波的混叠比例设计多次波滤波器,该滤波器能够根据一次波和多次波的混叠程度自适应调整滤波函数,提高多次波估计精度.合成数据和实际数据的多次波压制实验表明,这种频变滤波方法既可以改善多次波压制效果,又可避免高分辨率反演方法计算量大的问题.

基于Radon变换的时空图像纹理角识别方法

时空图像测速法以河流表面自然特征为分析对象,检测生成的时空图像中的纹理主方向,根据物象变换关系、拍摄所得视频参数和纹理方向倾角的正切值计算出河流表面的一维时均流速。针对实际应用中生成的时空图像受噪声干扰而导致时空图像纹理倾斜角检测精度出现较大误差的问题,本文提出采用改进的同态滤波器来增强河流表面图像的纹理特征,采用融合了自适应直方图均衡化的频域滤波对时空图像去噪,再利用Radon变换检测纹理角方向。通过模拟纹理图像实验,较高、较低流速条件下实地河道实验验证本文改进方法的有效性,实验结果表明,对于标准的模拟纹理图,Radon变换角度检测结果相对误差小于0.03%,对于干扰较多的复杂的实地河道环境,较低和较高流速条件下,基于Radon变换的时空图像纹理角识别结果与人工手动目测值间的相对误差分别小于1.56%和1.80%。实验表明,Radon变换法可行且较其他纹理角检测算法有更高的精度。

基于Radon变换的宽带信号多域参数同时测量方法

实际电子监测设备的作战环境复杂多变,辐射源个数、工作频率、工作带宽、到达角度等多域参数信息对于实现工作场景的实时精确感知至关重要。提出一种基于Radon变换的宽带信号多域参数同时测量方法,实现多个宽带信号多域重点工作参数的同时快速测量,大大提升低信噪比条件下监测目标特性的多维实时感知能力。该方法结合数字信道化结构及二重FFT算法实现全侦收频段及全侦收角度的空时域联合功率聚焦,并生成作战场景的空时二维频谱幅度图,利用Radon变换算法实现不同映射角度的线性积分运算,构建合适的检测门限,推导计算全场景多目标多参数测量结果。实验显示,该方法可以有效提升弱信号的参数测量精度,实现多目标多域参数同时测量。

基于Prewitt算子和Radon变换的雷达高速微弱目标检测

正交频分复用(OFDM)调制雷达中跨距离单元走动问题降低了高速微弱目标检测性能,为此,提出一种基于Prewitt算子和Radon变换的OFDM雷达高速微弱目标检测算法。首先分析了多脉冲积累出现的跨距离单元走动以及Radon变换受噪声干扰问题,然后采用Prewitt算子卷积运算抑制噪声并保留回波能量,采用Radon变换沿距离单元走动斜线进行能量积累。理论分析和仿真结果表明,该算法具有比Hough变换和动目标检测(MTD)更优的低信噪比背景下的高速微弱目标检测性能,并能有效实现多目标检测。

In-situ measurement via the flow-through method and numerical simulations for radon exhalation during measurements of the radon exhalation rate

Small-scale measurements of the radon exhalation rate using the flow-through and closed-loop methods were conducted on the surface of a uranium tailing pond to better understand the differences between the two methods.An abnormal radon exhalation behavior was observed,leading to computational fluid dynamics(CFD)-based simulations in which dynamic radon migration in a porous medium and accumulation chamber was considered.Based on the in-situ experimental and numerical simulation results,variations in the radon exhalation rate subject to permeability,flow rate,and insertion depth were quantified and analyzed.The in-situ radon exhalation rates measured using the flow-through method were higher than those measured using the closed-loop method,which could be explained by the negative pressure difference between the inside and outside of the chamber during the measurements.The consistency of the variations in the radon exhalation rate between the experiments and simulations suggests the reliability of CFD-based techniques in obtaining the dynamic evolution of transient radon exhalation rates for diffusion and convection at the porous medium-air interface.The synergistic effects of the three factors(insertion depth,flow rate,and permeability)on the negative pressure difference and measured exhalation rate were quantified,and multivariate regression models were established,with positive correlations in most cases;the exhalation rate decreased with increasing insertion depth at a permeability of 1×10^(−11) m^(2).CFD-based simulations can provide theoretical guidance for improving the flow-through method and thus achieve accurate measurements.

Numerical simulations for radon migration and exhalation behavior during measuring radon exhalation rate with closed-loop method

Accurate measurements of the radon exhalation rate help identify and evaluate radon risk regions in the environment.Among these measurement methods,the closed-loop method is frequently used.However,traditional experiments are insufficient or cannot analyze the radon migration and exhalation patterns at the gas–solid interface in the accumulation chamber.The CFD-based technique was applied to predict the radon concentration distribution in a limited space,allowing radon accumulation and exhalation inside the chamber intuitively and visually.In this study,three radon exhalation rates were defined,and two structural ventilation tubes were designed for the chamber.The consistency of the simulated results with the variation in the radon exhalation rate in a previous experiment or analytical solution was verified.The effects of the vent tube structure and flow rate on the radon uniformity in the chamber;permeability,insertion depth,and flow rate on the radon exhalation rate and the effective diffusion coefficient on back-diffusion were investigated.Based on the results,increasing the inser-tion depth from 1 to 5 cm decreased the effective decay constant by 19.55%,whereas the curve-fitted radon exhalation rate decreased(lower than the initial value)as the deviation from the initial value increased by approximately 7%.Increasing the effective diffusion coefficient from 2.77×10^(-7) to 7.77×10^(-6) m^(2) s^(-1) made the deviation expand from 2.14 to 15.96%.The conclusion is that an increased insertion depth helps reduce leakage in the chamber,subject to notable back-diffusion,and that the closed-loop method is reasonably used for porous media with a low effective diffusion coefficient in view of the back-diffusion effect.The CFD-based simulation is expected to provide guidance for the optimization of the radon exhalation rate measurement method and,thus,the accurate measurement of the radon exhalation rate.

二阶Radon-Fourier变换与遗传算法结合的快速相参积累算法

针对匀加速运动的高速目标,可以用二阶Radon-Fourier变换(Second-order Radon-Fourier Transform,SRFT)完成对回波信号的相参积累。SRFT算法的原理是通过“速度-加速度”联合搜索来实现目标的运动参数估计,其计算量较大,不满足实时检测的需求。针对这个问题,提出一种基于遗传算法(Genetic Algorithm,GA)的快速实现方法。首先对运动参数集进行编码,设置初始群体;然后通过遗传算法对群体更新迭代,使其能够自发快速地逼近全局最优解,减少不必要的搜索路径;最终快速实现待检测目标的相参积累。仿真结果表明,在保证检测性能的前提下,算法计算量得到有效改善,运算次数减少大约一个量级。

Measurement of Radon Concentration and Estimation of Cancer Risk in Twenty-Four Model Houses in the Town of Koudougou

The objective of our study is to evaluate the concentration of radon (86Rn) inside houses in the town of Koudougou in order to estimate its impact on the health of the population. Indeed, when uranium-rich minerals are found near the surface of the ground, radon concentrations can reach tens of becquerels per cubic meter in enclosed spaces. Given the nature of the geological base of Burkina Faso, this situation is quite probable and certain places that are sometimes poorly ventilated (house, school, office, etc.) can have radon levels high enough to constitute a health problem for occupants. Thus, twenty-four (24) sample houses were identified. In each house, the Corentium digital detector was between 0.8 m and 2 m for at least one week in a place where the occupants estimate that they spend more time of time and measure the concentration of radon in the long term and short term. The recorded data allowed us to determine the Absorbed Dose and the Annual Effective Dose of radon gas for each house in order to estimate the Risk of Cancer and the probable Number of Cases of Lung Cancer per million inhabitants. Thus, the results indicate that the long-term radon concentration varies between 6 Bq/m3 and 285 Bq/m3 respectively in houses 11 and 4 compared to 1 Bq/m3 to 208 Bq/m3 in the short term in the same houses. Also, in the long term, in control houses 1, 3 and 4, the radon level is above the recommended threshold interval. For the short term, these are houses 1, 3, 4 and 17 respectively with 110 Bq/m3, 142 Bq/m3, 208 Bq/m3 and 105 Bq/m3. As for the long-term and short-term effective doses, only houses 1, 3, 4, 17 and 24 have values between 3 - 10 Sv/year. The estimation of the relative risk of lung cancer gives values relatively close to unity and between 1.006 and 1.142 with an average of 1.035 and that of the Number of Lung Cancer Cases per million inhabitants gives values between 8 and 166 with an average of 42. Thus, we can conclude that with the exception of houses 1, 3, 4 and 17, the radon concentrations are relatively low in the twenty-four control houses in the city of Koudougou. The lifestyle of the populations can well explain this situation when we know that people are in the habit of always leaving doors and windows open, especially when they are not sleeping. We can therefore say that the risk of population exposure to radon gas is relatively low in the town of Koudougou.

Hurwitz-Radon矩阵方程的华罗庚链

1947年,华罗庚独立研究了Hurwitz-Radon矩阵方程,遗憾的是由于失误他未能得出完整结果。文章补充完善了华罗庚对于Hurwitz-Radon矩阵方程的求解。遵循华罗庚的思路,所采用的方法是矩阵的相似标准型。得到了华罗庚链,并通过酉化技巧得到其酉版本。

Measuring^(222)Rn in aquatic environment via Pulsed Ionization Chamber Radon Detector

Radon(Rn)is a naturally occurring radioactive inert gas in nature,and^(222)Rn has been routinely used as a powerful tracer in various aquatic environmental research on timescales of hours to days,such as submarine groundwater discharge.Here we developed a new approach to measure^(222)Rn in discrete water samples with a wide range of^(222)Rn concentrations using a Pulsed Ionization Chamber(PIC)Radon Detector.The sensitivity of the new PIC system is evaluated at 6.06 counts per minute for 1 Bq/L when a 500 mL water sample volume is used.A robust logarithmic correlation between sample volumes,ranging from 250 mL to 5000 mL,and system sensitivity obtained in this study strongly suggests that this approach is suitable for measuring radon concentration levels in various natural waters.Compared to the currently available methods for measuring radon in grab samples,the PIC system is cheaper,easier to operate and does not require extra accessories(e.g.,drying tubes etc.)to maintain stable measurements throughout the counting procedure.

基于线性Radon变换的超声混叠信号分离研究

在使用一发一收低频反射超声方法对大厚度介质进行测厚过程中,采集到的反射超声信号存在有效波和直达波混叠的现象,常规的一维超声信号处理方法难以对其进行有效处理。针对该类信号混叠问题,提出了基于线性Radon变换的自适应相减处理方法,从二维角度出发,根据在时空域中,直达干扰呈规律一致性,而有效底面回波呈推移差异性的特点,通过将信号阵列转换至线性Radon域的方法,对经过投影汇聚的信号数据进行自适应相减算法处理,实现对直达干扰波的有效压制及分离,从而提高低频超声回波数据的分辨率。通过仿真数据处理验证了该方法的有效性,相应厚度解算相对误差不超过0.7%。仿真和实验结果表明,提出的方法能够很好地解决大厚度介质测厚情境中混叠超声信号的分离问题。

海底反射时延广义Radon变换的无源定位

针对无源声呐目标定位问题,提出了一种基于广义Radon变换的目标参数估计方法。首先,基于深海直达声区推导了直达声与海底第一次反射声的到达时间差与目标运动参数的数学模型;其次,通过求解自相关函数得到目标的多途时延历程(MTDTR);在此基础上引入广义Radon变换的思想,联合两个水听器实现了水面匀速直航目标的航向角、速度、目标相对于水听器的初距和初始方位角估计。利用仿真数据和实验数据验证了该方法具有良好的参数估计性能。三亚东南部海域实验结果表明,通过两个锚系在深海海底附近的声压水听器对水面目标进行定位,可以实现在12.71 km范围内,测距误差小于0.29 km,相对误差小于3%的定位精度。