云的多次散射对激光雷达测量结果影响的研究

为了更加准确地获得大气消光系数和后向散射系数,利用半解析Monte Carlo方法对云的大气多次散射激光雷达回波信号进行了模拟计算。分析了激光雷达接收视场角及光学厚度对多次散射回波信号的影响及水云和卷云多次散射因子与光学厚度的关系。激光雷达测量数据的对比结果表明,多次散射对卷云和水云消光系数影响较明显,而对后向散射系数的影响可以忽略。     

中国人血液的组织光学参数

本文介绍了血液组织光学特性的测量原理与方法，并测量获得了不同血型的中国人血液的组织光学参数，包括血液吸收系数、散射系数、全衰减系数、平均散射余弦、有效衰减系数和穿透深度等。本研究对激光照射血液疗法以及其它激光照射人体组织的诊断与治疗，具有重要的实用或参考价值。     

多次散射的激光雷达消光系数反演方法研究

给出了在考虑多次散射时大气消光系数、后向散射系数的激光雷达反演方法.用半解析Monte-Carlo方法对大气多次散射激光雷达回波信号进行了模拟计算.讨论了激光雷达接收视场角(FOV)以及光学厚度对多次散射回波信号的影响.米散射激光雷达测量数据反演的结果表明,在反演含有云、雾等大气消光系数廓线分布时,需要考虑大气粒子的多次散射效应的影响.     

基于互相关函数法的超声无损测温研究

生物组织的声速随温度变化明显。利用信号处理技术中的互相关函数分析方法,计算超声散射回波信号的时间延迟。通过分析超声散射回波的时间延迟和组织温度的关系,提取生物组织的温度信息。实验结果表明:当以最高温度时的超声散射回波信号为基准信号时,不同温度时的超声散射回波信号与基准信号的时间延迟随着温度的降低而增大。该种处理方法可有效检测到超声散射回波信号的时间延迟随温度变化的趋势。     

液体激光聚焦击穿声辐射特性研究

激光与水介质相互作用时,在不同激光聚焦位置情况下,光击穿辐射声信号具有较大的差异性。为研究激光聚焦位置对辐射声波的影响,构建了激光声测量系统,实验研究了激光聚焦位置对光击穿辐射声信号的影响。结果表明,激光声信号脉冲宽度主要与激光脉冲宽度相关,与激光聚焦位置无关;激光聚焦位置影响声信号的时域波形及信号强度;应避免激光在空气中聚焦击穿。该研究结果有助于激光声研究的深入开展。     

用衍射光脉冲回波技术测量声光介质的体波声衰减系数

扼要介绍用衍射光脉冲回波技术测量声光介质体波声衰减系数的基本原理、实验装置和样品制备等，并分别测量了声光介质为石英玻璃、声光玻璃和ＬｉＮｂＯ３，ＰｂＭｏＯ４单晶的体波声衰减系数，给出了实验结果。     

浑浊水体激光后向散射特性仿真与实验研究

由于水体的吸收和散射作用,光束能量在传播的过程中会产生衰减,激光脉冲会被展宽,制约着水下激光雷达的探测范围和探测精度。文中以浑浊水体环境下水下弱小目标探测为应用背景,建立了水下光子传播的蒙特卡洛仿真模型,模拟了不同衰减系数和散射率的水体后向散射回波信号,并对相应的水体后向散射回波信号变化趋势进行了分析。仿真结果表明：随水体衰减系数的增加,近场水体激光回波信号接收光子数逐渐增多;随水体散射率的增加,回波信号光子消亡速度逐渐降低。开展了不同浊度下的激光雷达回波信号的测试实验,实验结果表明：随水体衰减系数的增加,水体激光后向散射回波幅度逐渐增高,脉冲宽度逐渐展宽。在进行浑浊水体水下弱小目标探测时,随水体衰减系数的增加,应通过逐渐减小激光器能量或接收系统增益来增强水体回波与目标回波之间的差异,以此提高浑浊水体水下弱小目标探测的信噪比。实验验证了理论与仿真结果,为浑浊水体环境下水下弱小目标激光探测系统在不同水质下的激光能量选取、接收系统增益设计等提供理论支撑。     

Mie散射激光雷达研究成都地区大气边界层特性

基于Mie散射激光雷达,对成都地区大气边界层结构随时间的变化特性进行了研究.利用Mie散射激光雷达测量大气回波信号,由改进的Klett算法反演获得大气后向散射系数,应用误差函数拟合法并参照位温廊线获得并分析了成都地区大气边界层高度以及卷夹层厚度等特性.     

检测散射元间距的多分辨率分析方法

本文研究了从生物组织的背向散射信号中提取散射元间距信息的多分辨率分析方法。从文中构造一维生物组织超声散射模型可以看到,散射元间距信息隐含在背向散射信号的低频包络中。本文采用绝对值检波方法作多分辨率分析的预处理,并采用能量最大准则确定检测的敏感尺度。仿真试验结果表明,这种方法可以有效地提取出背向散射信号中低频包络信息,准确地检测出散射元的位置;具有较强的抗噪性。     

激光雷达测量大气气溶胶光学厚度方法研究

介绍一种激光雷达常数标定和气溶胶光学厚度(AOD)测量的新方法.利用太阳辐射计,获得大气气溶胶的光学厚度,激光雷达可以获得35～40 km高度的回波信号,在这一高度区间可忽略气溶胶的存在,大气模式可以提供大气分子散射系数,根据激光雷达方程计算出激光雷达常数.反之,标定激光雷达常数后,根据激光雷达方程,以激光雷达35～40 km的大气分子后向散射回波信号来确定气溶胶的光学厚度.激光雷达测量结果与太阳辐射计的测量结果一致性较好,说明该方法是可行的.这种新方法既可以用于白天的气溶胶光学厚度测量,也可以用于夜间测量.     

脂肪-肌肉组织超声衰减特性的研究

基于超声脉冲反射原理,对脂肪-肌肉联合体沿纤维不同方向传播时的声速及其衰减规律进行研究。得到了超声波在组织中的衰减系数及声速值。实验结果表明:超声波沿不同纤维传播时,衰减系数和声速有所不同,即顺纤维传播的声速略大于横纤维方向传播,而横纤维方向传播的衰减系数则明显大于顺纤维方向。研究发现衰减系数及声速均具有随水分含量变化的特征,这对提高组织结构辨识能力,研究浅表软组织结构状态变化及临床应用提供实验依据。     

肌肉组织超声传输衰减特性的研究

探讨超声对肌肉组织超声传输特性。采用脉冲反射法,对肌肉组织沿纤维不同方向传播速度及其衰减规律进行研究。结果表明,对于肌肉组织,超声在顺纤维方向传播时,声速较大;在横纤维方向传播时,声衰减系数较大;水分含量多少对肌肉组织声速影响不大,而对衰减系数影响较大,其变化是影响组织声衰减的主要因素。这表明肌肉组织超声传输衰减特性具有随纤维方向结构变化特征,对研究生物软组织声学特性及其临床应用具有参考价值。     

The effects of rain on TOPEX/Poseidon altimeter data

The presence of rain in the sub-satellite track can significantly degrade altimeter measurements by causing an attenuation of the backscattered signal, a change in its path length through the atmosphere and a change in the mean square slope of the sea surface. This can cause errors, not only in the measurement of the satellite altitude, but also in the determination of wind speed and wave height. TOPEX/Poseidon dual-frequency altimeter data (cycles 3 and 8) were searched for instances where the data were possibly degraded by the presence of rain over the North and inter-Tropical Atlantic. A subjective analysis of the data, similar to the one used in previous studies was conducted on the backscatter coefficient, wind speed, significant wave height, sea surface height, TOPEX Microwave Radiometer (TMR) brightness temperatures, liquid water content and data quality flags to identify the orbits possibly affected by rain. From the 105 probable rain events identified, the effects of rain on the TOPEX measurements and data quality parameters were characterized. The strong differential effect of rain on the Ku and C band measurements was then used to define a new rain flag based on a departure from the normal relationship between the C and Ku band backscatter. This new rain flag was shown to detect all the identified rain events, as well as new ones. The TMR rain flag, used operationally, was shown to flag too many altimeter samples and too few rain events, mainly because of its large resolution (few tens of kilometers compared to few kilometers for the altimeter). An estimation of the rainfall rate from the attenuation of the Ku band backscatter was proposed     

Ultrasonic assessment of human and bovine trabecular bone: acomparison study

A comparison study is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and ultrasonic attenuation were evaluated through a transmission insertion technique and correlated with bone mineral density as determined with single photon absorptiometry. For a 1 MHz ultrasonic transducer pair and the human cancellous bone samples the correlations were 0.91 and 0.89 between density and velocity and attenuation, respectively. For a 500 kHz ultrasonic transducer pair the correlations were 0.89 and 0.81 between density and velocity and attenuation, respectively. For the bovine bone samples, the correlations were 0.90 and -0.31 for the velocity and attenuation, respectively, for the 1 MHz transducer pair. For the 500 kHz transducers, the correlations were 0.85 and -0.17 for the velocity and attenuation, respectively. By combining both velocity and attenuation in a multivariate regression, an improvement was achieved in the estimation of bone density in the human samples for both the 500 kHz and 1 MHz transducer pairs. No significant improvement was achieved in the multivariate regressions for the bovine bone samples. In conclusion, the results indicate that ultrasonic measurements are in general highly correlated with bone mineral density in trabecular bone samples. This correlation is more consistent and strong in relatively low density human samples compared with the higher density bovine samples     

海面水雾对激光传输的影响分析

为了研究水雾对激光传输的影响,采用理论分析与设备实测相比对的方法,对水雾的近红外消光特性进行了理论分析和实验验证,取得了海洋环境雾天不同能见度条件下的激光大气传输衰减特性测量数据及同等试验条件下的模拟计算对比数据。结果表明,海洋环境下,水雾是影响激光大气传输的主要因素,其消光系数量级在10-1km-1或100km-1,水雾对激光传输的衰减是大气分子散射和吸收所引起衰减的十几倍甚至几十倍;结合实测数据对经验常数C进行了修正,得到基于能见度的1.06m激光在海雾中衰减的经验公式。所得结果对科学评价激光对抗装备远场效能具有参考意义。     

High resolution ultrasonic backscatter coefficient estimation based on autoregressive spectral estimation using Burg's algorithm

An autoregressive (AR) method for spectral estimation was applied toward the task of estimating ultrasonic backscatter coefficients from small volumes of tissue. High spatial resolution is desirable for generating images of backscatter coefficient. Data was acquired from a homogeneous tissue-mimicking phantom and from a normal human liver in vivo. The AR method was much more resistant to gating artifacts than the traditional DFT (discrete Fourier transform) approach. The DFT method consistently underestimated backscatter coefficients at small gate lengths. Therefore backscatter coefficient image formation will be quantitatively more meaningful if based on AR spectral estimation rather than the DFT. The autoregressive method offers promise for enhanced spatial resolution and accuracy in ultrasonic tissue characterization and nondestructive evaluation of materials.     

Ultrasonics in chemistry

Measurements on the velocity and the attenuation of elastic waves in solutions can reveal changes internal to the solution, such as changes in the concentrations of the constituents. Any such change is characterized by a relaxation time, and the effect on velocity and attenuation is most apparent when the wave has angular frequency equal to the relaxation time; for many situations, such frequency lies in the range accessible to ultrasonic measurement. After developing the necessary background, this article describes the progress that has been made in applying ultrasonics to the chemistry of electrolytes.     

Analysis of algorithms for the retrieval of rain-rate profiles froma spaceborne dual-wavelength radar

The ability to retrieve rain-rate profiles from a dual-wavelength spaceborne radar system operating at 13.6 and 35 GHz is analyzed. The fundamental problem of extracting either the attenuation and/or the reflectivity from the backscatter echo, which contains both contributions, is addressed. Three algorithms, the backscatter, the attenuation coefficient, and the dual-wavelength methods, are examined. These algorithms are tested using four rain-rate profiles derived from radar measurements. In particular, measured (true) values are compared with calculated (retrieved) rain rates applying the algorithms with superimposed uncertainties assuming a suggested spaceborne dual-wavelength radar system. Error values of rain rates are determined where these values reflect failure of the assumptions utilized in the derivation of the algorithms, rain backscatter noise, and instrument noise     

基于双目立体视觉测量原理的物体运动速度测量

采用双目立体视觉测量系统进行炮弹速度的测量, 实现一种利用无速度测量因素测量设备测速的新方法。选择合适参数的两 台摄像机获得被测物体清晰的像,将两台摄像机搭建成光轴平行的双目视觉测量 系统,获得炮弹在运行过程中的每一时刻的三维轮廓数据,根据获得的三维数据进 行空间位置节点的三维插值,得到炮弹在t时间段内运行的距离,并求取平均 速度。仿真实验结果表明,本文方法可以准确、快速利用无速度测量因素的测量 设备获得炮弹的运行速度。     

Rain backscatter measurements at millimeter wavelengths

The US Army Ballistic Research Laboratory (BRL) conducted an experiment in 1973 to measure the properties of radar backscatter from rain at millimeter wavelengths. Rain backscatter and attenuation were measured with pulse radars operating simultaneously at 9.375, 35, 70, and 95 GHz over a wide range of rain intensities while continuous measurements of raindrop size and rainfall rate were made. This report describes the measurement technique, details of the instrumentation, the data analysis procedure, and the rain backscatter data obtained from A-scope photographs and video tapes