Comparison of three types of laser optical disdrometers under natural rainfall conditions

ABSTRACT

Optical disdrometers can be used to estimate rainfall erosivity; however, the relative accuracy of different disdrometers is unclear. This study compared three types of optical laser-based disdrometers to quantify differences in measured rainfall characteristics and to develop correction factors for kinetic energy (KE). Two identical PWS100 (Campbell Scientific), one Laser Precipitation Monitor (Thies Clima) and a first-generation Parsivel (OTT) were collocated with a weighing rain gauge (OTT Pluvio²) at a site in Austria. All disdrometers underestimated total rainfall compared to the rain gauge with relative biases from 2% to 29%. Differences in drop size distribution and velocity resulted in different KE estimates. By applying a linear regression to the KE–intensity relationship of each disdrometer, a correction factor for KE between the disdrometers was developed. This factor ranged from 1.15 to 1.36 and allowed comparison of KE between different disdrometer types despite differences in measured drop size and velocity.     

内蒙古霍各乞矿区含矿富石榴石岩晶体定量化结构分析及其意义

晶体粒度分布（CSD）是定量化分析火成岩和变质岩结构的重要手段。在变质岩中测量的CSD提供了有关变质过程中晶体成核和生长速率、生长时间的定量信息。文章选取内蒙古霍各乞二号矿床含矿富石榴石岩样品中石榴子石晶体为研究对象，在GIS软件和R语言的支持下，应用空间点模式分析、CSD分析、空间最邻近分析、空间多距离分析、Fry分析等综合方法，探讨了晶体空间数据和点空间数据表征的微结构变化特征，将CSD曲线分段变化记录的信息与地质演化历史联系起来。分段的CSD曲线记录了变质事件的叠加。不同形式的晶体粒度分布直接反映了区域变质岩与接触变质岩演化历史的差异。由于接触变质作用的高温阶段持续时间较短，因此产生的CSD曲线是线性的，不受退火的影响。而区域变质作用涉及长时间升温及其之后的冷却阶段，所以最初的线性CSD后来被退火改造为钟形曲线。含矿富石榴石岩样品的核密度和CSD分析结果显示了两个晶体群密度。分析认为一类晶体群可能与造山过程中的区域变质活动有关，另一类晶体群可能与大面积区域变质期后发生在特定位置的岩体侵入迅速升温的接触热变质事件有关。      

Monitoring alluvial sand suspension by eddy correlation

Eddy correlation techniques are standard tools in micrometeorology and oceanography to measure momentum and contaminant transport across turbulent boundary layers. They can, in theory, be used to estimate the net vertical suspended sediment flux directly over different areas of an alluvial channel boundary, and thus disclose ongoing erosion/deposition patterns. The basic principles and main problems in applying the technique to alluvial suspension are first introduced. Results from a trial application of the method in a large sand bed river are then presented; the focus of the analysis is on the substantial (and surprising) contributions of multi-minute flow fluctuations to suspension work in the study environment. The data were collected in a 10 m deep channel of the Fraser River near Mission, British Columbia, Canada. Turbulent fluctuations of flow components streamwise and normal to the bed, along with the output of an optical suspended sediment sensor, were monitored over 7 h, 1 m above the bed. Flow velocities averaged 0·9 ms^?1 and mean suspended sediment concentrations 500 mgl^?1, at sensor level above 1–5 dm high dunes. Spectral analysis of the records reveals that approximately 30 per cent of the vertical suspended sand mixing across the sensor level (and roughly as much of the momentum exchange) was linked to gradual flow oscillations with periods between 1 and 13·6 min (underlying briefer, turbulent fluctuations). Extended periods of sediment-rich, slightly upward directed but slower mean flow alternated with periods of sediment-poor, slightly downward and faster mean flow; these slow fluctuations involved 10–20 cms^?1 changes in 5 min average flow speed, 2–4· changes in vertical flow angle and 100 mgl^?1 changes in mean sand concentration. To obtain accurate eddy-correlation estimates of the vertical suspension flux in the study conditions, hour-scale flow and turbidity records that include many of these multi-minute cycles appear to be necessary. The spectra of the Fraser River near-bed signals do not conspicuously differ in overall shape (in terms of low-frequency content and location of peak) from turbulent spectra encountered in some atmospheric boundary layers. Nonetheless, the long period fluctuations observed on the Fraser River may not be turbulent; rather they may reflect slowly evolving perturbations in the near-bed streamlines, caused by bedform translation or gradual fluctuation within the large-scale streamwise cells of the secondary flow.     

Verification of a simple gravity technique for separation of particle size fractions suitable for mineral magnetic analysis

Techniques for the separation of sediment samples into size fractions are reviewed and the use of repeated decantations to provide samples for mineral magnetic analysis is described. Results from a series of trials are presented and compared with other techniques.     

高纬电离层中非麦克斯韦分布等离子体的非相干散射谱的模拟

使用一个修正的双麦克斯韦分布函数，通过最小均方适应技术使它与高纬电离层Ｆ区中离子的非麦克斯韦速度分布函数相适配．结果表明，使用这样的分布函数可以简化非相干散射谱的计算，并有助于简化高纬地区电离层非相干散射谱的反演．     

Raman Spectroscopy of Garnet—group Minerals

The Raman spectra of the natural end members of the garnet-group minerals,which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite ,andradite and uvarovite of Ca-Fe garnet series, have been strdied.Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the internal modes, translational and rotatory modes of SiO4 tetrahedra, as well as the translational motion of bivalent cations in the X site.The stretch and rotatory A1g modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series ,owing to the cations residing in the Xsite connected with SiO4 tetrahedra by sharing the two edges.The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series andin the Y site for the Ca-Fe garnet series.     

Seismic ground motion in a layered half-space due to a Haskell-type source. I: Theory

In this paper, closed-form analytic expressions for the frequency-wave number domain Fourier amplitudes of the displacement field at the free surface of a layered, anelastic half-space are established. The displacement field is caused by a seismic source described by a shear dislocation propagating with constant velocity over a rectangular fault (Haskell's model). Three-dimensional plane wave propagation is considered in the layered half-space using a propagator-based formalism. The wave radiation from the source is decoupled into P-SV and SH motions and the two problems are treated separately. First, analytic expressions are calculated for the displacement field at the free surface due to unidirectional unit impulses. Then, these expressions are used to compute solutions for the displacement field due to effective point sources associated with a pure strike slip and a pure dip slip. Finally, these solutions are combined and integrated over the rectangular fault area to establish closed-form analytic expressions of the total displacement field at the free surface.     

A multivariate sedimentary environmental analysis of Great South Bay and South Oyster Bay, New York

A multivariate statistical strategy for classifying paleoenvironments is effective for studying modern sedimentary processes in western Great South Bay and South Oyster Bay, New York. The 13 whole phi weight percent variables were tested for redundancy with R-mode cluster analysis. The samples were partitioned statistically into five environmentally significant facies using Q-mode cluster analysis: (A)sandy gravel, (B)sandy silt, (C)silty sand, (D)slightly gravelly sand, and (E)fine sand. An ordination depicted gradational relationships among the samples and the facies. It was used to evaluate the environmental and textural parameter gradients within the sample space. Interpretations obtained in this manner and by examination of the grain-size curves suggest that these sediments were deposited by waves and currents on beaches and in wave zones (facies C and E),shoal areas (facies B),and tidal channels (facies A and D).Tidal currents, wave action, and eelgrass control the distribution of sediments within the two bays.     

Theory and applicability of a recrystallized grain size paleopiezometer

An approximate theoretical relation is derived which relates stress during steady state creep to both subgrain size and dynamically recrystallized grain size. The relation results from equating the dislocation strain energy in the grain boundary to that in the enclosed volume. Available data on metals and silicates are in excellent agreement with the theory. For paleopiezometry, the recrystallized grain size must be preserved by quenching, by cooling under stress, or by inhibition of grain growth by intimate mixture of two or more phases. In general, stress may be underestimated using rocks in which grain size has been reduced by dynamic recrystallization, especially if the grain size is very small. Stress may be overestimated using coarse grained rocks in which the grain size has increased toward the steady state value. Quantitative limits remain to be established. The theoretical relation can in principle be applied to any metal or mineral if only the effective isotropic elastic moduli and the Burgers vector are known. When used as a paleopiezometer, the technique indicates that high stresses on the order of 100 MPa are not infrequently associated with mantle diapirism and with large scale thrust faulting. Consideration of the Mt. Albert ultramafic body suggests that texturally inferred stresses from peridotite massifs and from ultramafic xenoliths in alkali olivine basalts might reflect either horizontal variations in stress across a rising diapir or else a vertical variation in stress as defined by the pyroxene geobarometer (Mercier et al. 1977). In either case the stresses are probably characteristic of local diapirism. Stresses characteristic of global upper mantle flow might be inferred from xenoliths originating from above kimberlite-producing diapirs.