云台激光测距系统单光子雪崩二极管探测器的精确调整

灵敏度达单光子水平的崩二极管,是目前为止可用于激光测距的最好探测器,国际上多数测距站都采用这种探测器.单光子雪崩二极管探测器的优点是灵敏度、时间响应和暗噪声等性能指标都十分优越,缺点是视场小,视场角仅53',这对于测距是不利的.为了使用好单光子雪崩二极管探测器,充分发挥它的作用,我们建立了专用的回波调整准直光源,设计了专门的单光子雪崩二极管探测器调整架,并应用噪声计数方法对单光子雪崩二极管探测器做了非常精细的调整,使其很好地为激光测距工作服务.     

白噪声中f~(-2)随机过程的最优估计

从功率谱的角度分析了白噪声中f-2随机过程的最优估计问题，推导了线性估计方法的精度极限，并通过对若干线性估计方法的精度进行分析和比较，得到了一些有意义的结论。     

Hyperspectral image noise reduction based on rank-1 tensor decomposition

In this study, a novel noise reduction algorithm for hyperspectral imagery (HSI) is proposed based on high-order rank-1 tensor decomposition. The hyperspectral data cube is considered as a three-order tensor that is able to jointly treat both the spatial and spectral modes. Subsequently, the rank-1 tensor decomposition (R1TD) algorithm is applied to the tensor data, which takes into account both the spatial and spectral information of the hyperspectral data cube. A noise-reduced hyperspectral image is then obtained by combining the rank-1 tensors using an eigenvalue intensity sorting and reconstruction technique. Compared with the existing noise reduction methods such as the conventional channel-by-channel approaches and the recently developed multidimensional filter, the spatial–spectral adaptive total variation filter, experiments with both synthetic noisy data and real HSI data reveal that the proposed R1TD algorithm significantly improves the HSI data quality in terms of both visual inspection and image quality indices. The subsequent image classification results further validate the effectiveness of the proposed HSI noise reduction algorithm.     

利用厦门—连城临时测线记录提取面波格林函数

本文利用沿厦门—连城测线布设的20个临时观测台的记录, 结合近年发展起来的利用噪声提取面波格林函数的技术, 提取了这20个临时观测点两两间的面波格林函数。 结果表明, 40天的噪声数据完全可以得到信噪比较高的面波格林函数, 这可能和该测线与海岸线近似垂直, 能量主要由沿海传向内陆有关。 根据所有射线每天的面波格林函数随时间推移的变化, 指出S04观测点在此次临时观测期间存在1.5~2.0 s的授时误差, 这可很好的解释爆破观测中出现的震中距与波形到时的颠倒现象; 并且, 利用爆破记录的观测到时验证了“华南地区近震走时表”在该地区的适用性。     

GOCE卫星重力测量中有色噪声滤波器设计

本文根据卫星重力梯度测量的有色噪声特性,设计了Wiener、AR、FIR三种滤波器,并利用模拟的有色噪声数据对其滤波效果进行了测试,结果表明:对于文中采用的有色噪声数据,AR的滤波效果最好,其次为Wiener滤波器,FIR的滤波效果最差;三种滤波器均可用于GOCE卫星重力测量中有色噪声数据滤波,但其实用性尚需利用实测数据进行检验;可以利用不同的滤波器对含有色噪声的卫星重力梯度数据进行多次滤波,以进一步减弱有色噪声对卫星重力梯度测量精度的影响.     

Behavioral responses of a harbor porpoise (Phocoena phocoena) to playbacks of broadband pile driving sounds

The high under-water sound pressure levels (SPLs) produced during pile driving to build offshore wind turbines may affect harbor porpoises. To estimate the discomfort threshold of pile driving sounds, a porpoise in a quiet pool was exposed to playbacks (46 strikes/min) at five SPLs (6 dB steps: 130–154 dB re 1 μPa). The spectrum of the impulsive sound resembled the spectrum of pile driving sound at tens of kilometers from the pile driving location in shallow water such as that found in the North Sea. The animal's behavior during test and baseline periods was compared. At and above a received broadband SPL of 136 dB re 1 μPa [zero-peak sound pressure level: 151 dB re 1 μPa; t₉₀: 126 ms; sound exposure level of a single strike (SEL_ss): 127 dB re 1 μPa² s] the porpoise's respiration rate increased in response to the pile driving sounds. At higher levels, he also jumped out of the water more often. Wild porpoises are expected to move tens of kilometers away from offshore pile driving locations; response distances will vary with context, the sounds' source level, parameters influencing sound propagation, and background noise levels.     

华北科学探测台阵背景噪声特征分析

利用华北科学探测台阵180多个宽频带台站2007年的连续记录,得到了台站之间噪声互相关函数.通过对三个分量记录的相关运算,获得了Rayleigh波和Love波的经验格林函数,分析了其信噪比随周期的变化和高信噪比台站对的方位分布.利用经验格林函数的非对称性和聚束方法,研究了华北科学探测台阵地震噪声的方位分布,及其季节变化特征.尽管噪声源的分布随季节有轻微变化,但全年的分析结果表明,10～32 s周期内华北台阵的地震噪声源在各个方向上的分布近于均匀,这为利用噪声成像提供了理论前提.     

From noise correlation to resonant ultrasound spectroscopy in rock acoustics

This article introduces an alternative experimental procedure for measuring the elastic properties of a solid material at laboratory scale, using both the principles of passive seismic interferometry and resonance ultrasound spectroscopy. We generate noise into the studied sample with a pneumatic air blow gun, and we cross‐correlate the signals recorded with two passive piezoelectric sensors put in soft contact with the sample surface. Resonance phenomena are induced in the sample, but in contrast with conventional resonance ultrasound spectroscopy experiments, we have no control over the injected frequencies that are sent all together within the noise spectrum. The spectrum of the correlogram is a good approximation of the resonance spectrum of the vibrating sample and can be inverted in terms of the elastic moduli of the constituent material of the sample. The experimental procedure is validated on samples made of standard materials (here, aluminium and Plexiglas) by consistently comparing the inverted elastic velocities with the velocities independently measured with the conventional technique of ultrasonic pulse transmission. Moreover, we got similar positive results on dry rock samples, such as Vilhonneur limestone. These encouraging preliminary results open up promising prospects for monitoring fluid substitution in rock samples using the technique described in this paper.     

用扩散电场法估算CHTEM-I系统的探测深度

时间域航空电磁系统的探测深度是一项关键技术参数,在系统研制设计和资料解释中都有重要作用.当目标层与围岩电性差异不大或目标层引起的异常响应不明显时,常规的估算探测深度方法不再适用,为克服这种缺陷,本文提出了一种系统探测深度的估算方法,该方法通过模拟电场在均匀半空间模型和层状模型中的扩散过程,记录电场最大幅值在地下的瞬时位置,将系统的探测深度定义为观测到的响应值等于给定的噪声水平时,对应时刻的地下介质中感应电场幅度的最大值对应的深度.论文以我国自主研制的直升机时间域航空电磁系统CHTEM-I为例,根据对不同条件下的计算结果的分析,给出了探测深度与模型电导率、飞行高度和噪声水平之间的关系曲线,并总结出一些能够提高系统探测深度的建议.结果表明半空间模型电导率在0.000295~0.0422 S/m范围内,CHTEM-I系统可以在噪声水平与t^－0.5成正比条件下达到300 m的探测深度.本文方法的估算结果不受模型层厚薄,或目标层与围岩电性差异小等因素影响,因而具有较高的实用性.文中的结论对时间域航空电磁系统设计有理论指导意义,也可用于其它时间域电磁勘探系统探测深度的估算.     

基于同步大地电磁时间序列依赖关系的噪声处理

本文从信号与系统的角度讨论了同步大地电磁时间序列信号之间的依赖关系,选取高信噪比的时间序列信号作为先验数据,用最小二乘法估算依赖关系;结合参考道的数据,合成本地道含噪声时段的数据,最后用合成数据替代噪声段数据,组成新数据,从而在时域中去除大地电磁噪声.西藏地区高信噪比实测数据的试算结果表明,无论电场还是磁场,信号之间的依赖关系是相对稳定的,只与先验数据的长度有关,与时间无关;虽然不同参考点之间的依赖关系不同,但都可以精确合成本地点数据,与参考点地下电性结构和参考距离无关.仿真实验显示,去噪后的信号与原始信号基本一致.实测数据处理结果表明,该方法可以有效去除强噪声干扰,抑制中高频段的近场源效应,同时保留了微弱的有效信号,保证了处理结果的正确性.最后针对方差比方法无法识别的方波噪声,提出了一种简单的平移方法,成功去除了持续时间大于窗口长度的方波噪声;将该方法与远参考技术结合,可以有效抑制近场源噪声干扰,获得光滑连续并且可信的测深资料.