Effect of changes in fine‐grained matrix on bedload sediment transport in a gravel‐bed river

While clay and silt matrices of gravel‐bed rivers have received attention from ecologists concerned variously with the deteriorating environments of benthic and hyporheic organisms, their impact on sediment entrainment and transport has been explored less. A recent increase of such a matrix in the bed of Nahal Eshtemoa, an ephemeral river of the northern Negev, has more than doubled the boundary shear stress needed to initiate bedload, from 7 N m^‐2 (τ^* = 0.027) during the flash floods of 1991–2001 to 15 N m^‐2 (τ^* = 0.059) during those of 2008–2009. The relation between bedload flux and boundary shear stress continues to be well‐defined, but it is displaced. The matrix now contains a significant amount of silt and clay size material. The reasons for the increased entrainment threshold of bedload are explored. Large‐scale laser scanning of the dry bed reveals a reduction in grain‐scale morphological roughness, while artificial in situ tests of matrix integrity indicate considerable cohesion. The implications for adopting bed material sampling strategies that account for matrix development are assessed. Copyright © 2012 John Wiley & Sons, Ltd.     

A Review of “The Power of Place”

Two qualitative case studies, one focusing on K-12 teachers and the other on middle school students, explore key factors associated with using Geographic Information Systems in the classroom. In both studies, access to appropriate hardware is a critical barrier. Time is another critical barrier—time to learn the GIS software and time in the curriculum to incorporate GIS as a learning experience. In both case studies, learning the technology at the expense of learning spatial analysis was a danger, suggesting the need for conscious focus on the goal of using GIS to learn how to “do geography.”     

Comparison among sea surface roughness schemes

1 INTRODUCTIONIt is well known that wind-generated wavestorm surge and atmospheric circulation as impor-tant ocean weather events are closely related tomomentum exchange between sea and atmosphere(Oncley and Dudhia, 1995). For this reason, in thepast 20 years, attention has been directed towardshow to better describe momentum exchange throughsea surface. In general, to precisely determine theexchange, improvement should be made in the as-pects of reasonably depicting the roughness de-pend…     

Underestimation of roughness in rough rock joints

Numerous studies have been made to improve Barton's shear strength model for the quantification of rock joints. However, in these previous studies, the roughness and shear strength of the rock joint have been underestimated especially for relatively high undulated profiles (joint roughness coefficient (JRC) >14). The main factors of roughness underestimation in rough rock joints are investigated for the proper quantification of rock joint roughness. The aliasing effect and the roughness characteristics are analyzed by using artificial joint profiles and natural rock joint profiles. A 3D camera scanner is adopted to verify the main source of underestimation when using conventional measurement methods. Shear strength tests are carried out by using two types of shear apparatus to study the roughness mobilization characteristics, which may also affect the roughness underestimation. The results of joint roughness assessment, such as aliasing and undulation of waviness, show that the roughness can be underestimated in relatively rough joint profiles (JRC>14). At least two components of roughness parameters are needed to properly represent the joint roughness, for example, the amplitude and the inclination angle of joint asperity. Roughness mobilization is affected by both the normal stress and the asperity scale. Copyright © 2008 John Wiley & Sons, Ltd.     

A new calibration of the effective scattering albedo and soil roughness parameters in the SMOS SM retrieval algorithm

This study focuses on the calibration of the effective vegetation scattering albedo (ω) and surface soil roughness parameters (H_R, and N_Rp, p = H,V) in the Soil Moisture (SM) retrieval from L-band passive microwave observations using the L-band Microwave Emission of the Biosphere (L-MEB) model. In the current Soil Moisture and Ocean Salinity (SMOS) Level 2 (L2), v620, and Level 3 (L3), v300, SM retrieval algorithms, low vegetated areas are parameterized by ω = 0 and H_R = 0.1, whereas values of ω = 0.06 − 0.08 and H_R = 0.3 are used for forests. Several parameterizations of the vegetation and soil roughness parameters (ω, H_R and N_Rp, p = H,V) were tested in this study, treating SMOS SM retrievals as homogeneous over each pixel instead of retrieving SM over a representative fraction of the pixel, as implemented in the operational SMOS L2 and L3 algorithms. Globally-constant values of ω = 0.10, H_R = 0.4 and N_Rp = −1 (p = H,V) were found to yield SM retrievals that compared best with in situ SM data measured at many sites worldwide from the International Soil Moisture Network (ISMN). The calibration was repeated for collections of in situ sites classified in different land cover categories based on the International Geosphere-Biosphere Programme (IGBP) scheme. Depending on the IGBP land cover class, values of ω and H_R varied, respectively, in the range 0.08–0.12 and 0.1–0.5. A validation exercise based on in situ measurements confirmed that using either a global or an IGBP-based calibration, there was an improvement in the accuracy of the SM retrievals compared to the SMOS L3 SM product considering all statistical metrics (R = 0.61, bias = −0.019 m³ m⁻³, ubRMSE = 0.062 m³ m⁻³ for the IGBP-based calibration; against R = 0.54, bias = −0.034 m³ m⁻³ and ubRMSE = 0.070 m³ m⁻³ for the SMOS L3 SM product). This result is a key step in the calibration of the roughness and vegetation parameters in the operational SMOS retrieval algorithm. The approach presented here is the core of a new forthcoming SMOS optimized SM product.     

南极内陆冰盖表面地貌特征监测系统设计及应用分析

南极内陆冰盖表面的特征与冰盖表面年际降雪量、冰盖表面风速有关,冰盖表面地貌特征主要包括雪面粗糙度、雪层软硬度,这些特征对内陆车队行进过程中的设备运输具有重要的参考价值。文中提出了车载自动化监测冰盖雪面特征的方法,并进行了监测系统的设计与数据分析;该系统包括以雪地车颠簸幅度代表的雪面凹凸程度(即雪面粗糙度),以GPS模块监测车辆行进距离,以激光测距监测雪地车车辙深度来表征雪面软硬度。通过数据采集系统的实时监测软件平台,实现了冰盖表面地貌特征的监测;该系统分别于2012年11月和2014年11月在中国第29次南极和31次南极考察中进行了监测应用,通过对以上监测数据的分析,初步给出了中山站至昆仑站沿途的冰盖表面粗糙度及雪面软硬度结果。     

基于二维激光观测的溢油及其乳化过程散射模式研究进展

合成孔径雷达(SAR)以其高分辨率、能不受雨云影响实施全天时全天候全方位监测,在海面溢油灾害应急监测过程中发挥着越来越重要的作用。溢油是因为海面油膜抑制了毛细波和重力波,在SAR图像上呈暗斑而被识别。然而,海面溢油的乳化过程直接影响SAR对海面溢油后向散射截面的观测精度。本研究以物理海洋学和激光原理以及海面电磁散射理论为基础,通过实验利用激光扫描仪观测海面溢油粗糙度,分别与溢油特征参数、后向散射系数建立对应关系;耦合海面溢油参数与后向散射截面的关系,利用电磁散射数值建模方法,建立海面溢油散射模型,研究海面溢油乳化过程对微波后向散射截面的影响。本项目的研究将为SAR监测海面溢油量、溢油厚度及油品分布格局提供了可能;将进一步揭示海面溢油的散射机制,提高SAR海面监测溢油的精度和能力。     

冰封河道综合糙率计算方法比较与分析

综合糙率是冰封河道水力计算的重要输入参数。根据水流连续性和力的平衡原理,分别推导得到冰封河道综合糙率的通用公式,并选取抛物线形、矩形和梯形作为典型断面,系统地总结Pavlovskiy、Einstein、Lotter、Sabaneev、Larsen、改进的Larsen等常见公式由通用公式基于何种假定（分区的湿周、流速或水力半径相等）简化得到。采用水槽实测数据和野外观测资料,对比上述公式的计算精度,结果表明改进的Larsen公式的计算结果与实测值吻合较好,推荐在工程设计中使用。前5种公式误差较大的原因在于分区的流速、水力半径相等对于冰封河道不具有普适性,尤其是Lotter公式和Pavlovskiy公式在冰盖和河床糙率差异较大时会明显低估冰封河道的综合糙率,在工程设计中应慎重采用。     

硬性结构面粗糙度系数量化确定及其工程应用

本文通过对硬性节理表面粗糙度系数JRC量化确定的研究,对包括Barton推荐标准曲线在内的大量结构面起伏曲线矢量化分析,利用期望值的概念反映结构面起伏曲线粗糙度JRC,建立JRC与起伏曲线高度、坡度两个因素的经验公式,为Barton理论公式法快速预测结构面参数提供了充足条件,并用理论公式法预测成果与试验成果进行对比分析。