Influence of long‐period filter cut‐off on elastic spectral displacements

The effect of the long‐period filter cut‐off, T_c, on elastic spectral displacements is investigated using a strong ground‐motion database from Europe and the Middle East. The relation between the filter and oscillator responses is considered to observe the influence of T_c for both analogue and digital records, and the variations with site classification, magnitude, filter order and viscous damping. Robust statistics are derived using the re‐processed European data to generalize the effects of the long‐period filter cut‐off on maximum oscillator deformation demands as a function of these seismological and structural features. Statistics with a 95% confidence interval are derived to suggest usable period ranges for spectral displacement computations as a function of T_c. The results indicate that the maximum period at which spectral displacements can be confidently calculated depend strongly on the site class, magnitude and filter order. The period range where reliable long‐period information can be extracted from digital accelerograms is twice that of analogue records. Copyright © 2006 John Wiley & Sons, Ltd.     

The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure?

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.     

Wavelet filter analysis of atmospheric pressure effects in the long-period seismic mode band

The importance of the reduction of atmospheric pressure effects becomes very clear when investigating seismic normal-mode spectra below 1.5 mHz. The usual simple correction method consists in subtracting a term converted from local atmospheric pressure (pressure multiplied by a frequency-independent admittance) from the gravity record in time domain. Thus, estimating an efficient admittance is the key for an improved correction. Band-pass filters derived from dyadic orthogonal wavelet transform, having narrow pass-bands with good frequency response but without Gibbs phenomenon and causing no phase lag, are very helpful to estimate an efficient admittance, which is both time and frequency-dependent. Processing of high quality superconducting gravimeter (SG) records for the great Sumatra earthquake (Mw = 9.3, Dec 26, 2004) with wavelet filters reveal the three very well resolved splitting singlets of overtone ₂S₁ with a single gravity record after correction with time-dependent and frequency-dependent admittances. We also observe all coupled toroidal modes below 1.5 mHz, except ₀T₅, ₀T₇ and ₁T₁, with good signal-to-noise ratio (SNR); moreover, toroidal modes ₁T₂ and ₁T₃ are for the first time unambiguously revealed in vertical components.     

MT时间序列的FIR数字滤波分析

大地电磁测深法(MT)野外观测得到的原始资料是包含多种频谱的时间序列,这种时间序列中常包含不需要的信息和50 Hz及其谐波的干扰。结合FIR数字滤波技术与MT时间序列的特征,提出了一种基于FIR数字滤波技术的MT时间序列去噪方法,讨论了FIR数字滤波器的原理和实现,分析了理论数据通过FIR数字滤波的带通和陷波处理,探讨了对实测时间序列的带通和陷波所取得的效果。     

矿物材料应用于香烟过滤嘴降害的研究现状与展望

总结了近几十年来包括活性炭、沸石、蒙脱石、海泡石、麦饭石、凹凸棒石、氧化铝、氢氧化钠、明矾、纳米材料等矿物材料作为卷烟滤嘴添加剂以去除烟气中有毒有害物质的研究和实验应用及效果。实验结果和市场调查表明,活性炭是减少卷烟危害最快、香烟市场应用增长最快的过滤嘴添加剂。从降低卷烟有害成分的比例和成本等综合因素来看,铝硅酸盐类滤嘴和多材料复合滤嘴亦有很好的应用前景和市场需求,应积极进行研制。     

JMD型滤池双层滤料的净水试验及比较

大量的试验数据表明石英砂和陶粒组成的双层滤料，其净水处理性能明显好于石英砂和无烟煤双层滤料以及单层石英砂滤料，特别是出水浊度、微絮凝作用，反冲洗周期、藻类的去除、絮凝剂的使用量等指标上具有明显优势，陶粒做为一种新的水处理滤料，正被应用于净水和污水处理。     

陆相沉积的天文地层研究方法简介——以井下地层为例

通过对我国大陆三十余口井的测井资料研究成果,归纳出对陆相地层进行天文地层研究的方法。介绍了所用的新的天文周期理论值、测井资料的选取及预处理方法,重点说明谱分析的数据点数的选定、不同参数(自然伽玛、自然电位和岩屑)的测井资料谱分析结果的对比,以实例说明如何选定主要优势旋回和AR值,以及FIR数字滤波器的基本性质和数字滤波结果,小波分析的特点和通过小波图进行调频的方法,并介绍了地层单位的延续时间计算和年龄确定方法。     

A method to improve the alignment performance for GPS-IMU System

Zero velocity and zero east component of rotation rate relative to local geographic frame have been traditionally applied as measurements for fine alignment of a GPS-IMU system. The performance of the fine alignment, however, will be affected by several types of inertial sensor errors, which could cause part of the Kalman filter states to be unobservable. To overcome this problem, a new method that utilizes the total outputs of the gyro triad and the accelerometer triad as part of the measurements has been proposed by the authors. The initial results have confirmed the effectiveness of the method. In this paper, the observability for both traditional and new alignment methods will be first reviewed. The results from computer simulations will then be presented to compare the traditional and the new alignment methods for the purpose of evaluating the performance of the proposed new method. Data acquired from real inertial sensors will also be applied to assess the traditional and new alignment methods by analyzing their innovation sequences from the Klaman filter. Based on a paper presented at the 18th International Technical Meeting of the Satellite Division of the Institute of Navigation, Long Beach, California, September 2005.     

GPS sidereal filtering: coordinate- and carrier-phase-level strategies

Multipath error is considered one of the major errors affecting GPS observations. One can benefit from the repetition of satellite geometry approximately every sidereal day, and apply filtering to help minimize this error. For GPS data at 1 s interval processed using a double-difference strategy, using the day-to-day coordinate or carrier-phase residual autocorrelation determined with a 10-h window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 h can produce an acceptable value with > 97% of the optimal lag’s correlation. We conclude that although the lag may vary with time, such variation is marginal and there is little advantage in using a satellite-specific or other time-varying lag in double-difference processing. We filter the GPS data either by stacking a number of days of processed coordinate residuals using the optimum “sidereal” lag (23 h 55 m 54 s), and removing these stacked residuals from the day in question (coordinate space), or by a similar method using double-difference carrier-phase residuals (observational space). Either method results in more consistent and homogeneous set of coordinates throughout the dataset compared with unfiltered processing. Coordinate stacking reduces geometry-related repeating errors (mainly multipath) better than carrier-phase residual stacking, although the latter takes less processing time to achieve final filtered coordinates. Thus, the optimal stacking method will depend on whether coordinate precision or computational time is the over-riding criterion.     

逐次滤波方法在GPS单点定位中的应用研究

采用平差计算中得到的观测值的残差来估计指数函数经验模型中的参数，从而使随机模型更真实地反映观测值中的随机误差和偏差。由实际GPS观测数据厦广播里历，按以上的函数模型和随机模型采用逐次滤波方法进行解算。结果表明，此方法在未剔除和修复周跳的情况下，可以使单点静态定位的平面外符合精度达1．46m，高程方向的外符合精度为1．72m。