Sensitivity of the backscatter intensity of ALOS/PALSAR to the above-ground biomass and other biophysical parameters of boreal forest in Alaska

We investigated the potential of ALOS/PALSAR for estimating the above-ground biomass (AGB) and other biophysical parameters (tree height, diameter at breast height (DBH), and tree stand density) in the boreal forest of Alaska. In July 2007, forest surveys were conducted along a south–north transect (150°W) to profile the ecotone from boreal forest to tundra in Alaska. In situ parameters were measured in 29 forests by a combination of the Bitterlich angle-count sampling method and the sampled-tree measuring method. These in situ values were compared with the backscatter intensity of ALOS/PALSAR. A strong positive logarithmic correlation was found between the backscatter intensity and the forest AGB, with the correlation being stronger in the HV than in the HH polarization mode. No obvious saturation was found in the sensitivity of the HV mode backscatter intensity to the forest AGB up to 120.7 Mg ha^?1. Similarly, a robust sensitivity was found in the HV backscatter intensity to both tree height and DBH, but weak sensitivity was observed for tree density. The regression curve of HV backscatter intensity to the forest AGB appeared to be intensified by the uneven forest floor, particularly for forests with small AGB. The geographical distribution of the forest AGB was mapped, demonstrating a generally south-rich and north-poor forest AGB gradient.     

Evaluating the Accuracy and Effectiveness of Criminal Geographic Profiling Methods: The Case of Dandora,Kenya

Criminal geographic profiling (CGP) prioritizes offender search, extensively reducing the resources expended in criminal investigations. The utility of CGP has, however, remained unclear when variations in environmental characteristics and offense type are introduced. This study evaluates several CGP strategies with data from Dandora, a small but densely populated suburb of Nairobi, Kenya. The research employs error distance and search-cost measures to determine CGP accuracy. Characterized by much shorter journeys to crime than those observed in Western cities, this study discovers significant applicability of CGP strategies in prioritizing offender searches. The negative exponential CGP strategy is identified to generate the most accurate geo-profiles.     

Disaggregation modelling of monthly streamflows using a new approach of the method of fragments

Abstract

The method of fragments is applied to the generation of synthetic monthly streamflow series using streamflow data from 34 gauging stations in mainland Portugal. A generation model based on the random sampling of the log-Pearson Type III distribution was applied to each sample to generate 1200 synthetic series of annual streamflow with an equal length to that of the sample. The synthetic annual streamflow series were then disaggregated into monthly streamflows using the method of fragments, by three approaches that differed in terms of the establishment of classes and the selection of fragments. The results of the application of such approaches were compared in terms of the capacity of the method to preserve the main monthly statistical parameters of the historical samples.

Editor D. Koutsoyiannis; Associate editor C. Onof

Citation Silva, A.T. and Portela, M.M., 2012. Disaggregation modelling of monthly streamflows using a new approach of the method of fragments. Hydrological Sciences Journal, 57 (5), 942–955.     

A continuous simulation model for design-hydrograph estimation in small and ungauged watersheds

Abstract

A detailed investigation of the behaviour of various hydraulic parameters, using data from rivers in Greece, was conducted in order to explore the universality of features that many natural streams are believed to have in common. Analysis of vertical profiles of temporal mean of horizontal velocities (u) in the longitudinal (river flow) direction and of transverse profiles of depth-mean longitudinal velocities (U) estimated from these vertical profiles, measured at 232 cross-sections of several rivers in Greece, provided valuable information: on the distribution of local roughness coefficients (n_i ) along the wetted perimeter of the cross-sections examined; on the shape of u profiles; on the ratio of maximum to mean cross-sectional velocity, V_max/V_m , and its relation to a dimensionless entropy parameter, M; on the shape of U profiles; and on the normalized intensity, r, of the spatial departure of u velocities from V_m . The similarities among the quantities (u, U, n, V_max/V_m , M, r) analysed in this study and in pertinent literature reveal that the rivers examined exhibit many of the basic features, of rather universal character, shown by other rivers (all over the world) having different geometric and/or other characteristics (aspect ratios, bottom roughness, flow kinematics, etc.). Corresponding differences are also described and explained.     

B) Organisations internationales

Abstract

A modification of Svanidze's fragments method was applied to generate synthetic samples of monthly inflows to the La Angostura and Malpaso dams, located on the Grijalva River, in the state of Chiapas, Mexico. This modification allows generation of the monthly runoff of several dams in a series and preservation of their cross-correlations. Comparing statistics of generated and historical series, a good agreement between them was observed, especially for the autocorrelations between consecutive months and for cross-correlations between both dams, except for slight differences in the standard deviation and the skewness during the dry period.     

Dam risk assessment based on univariate versus bivariate statistical approaches: a case study for Argentina

Abstract

Considering floods as multivariate events allows a better statistical representation of their complexity. In this work the relevance of multivariate analysis of floods for designing or assessing the safety of hydraulic structures is discussed. A flood event is characterized by its peak flow and volume. The dependence between the variables is modelled with a copula. One thousand random pairs of variables are transformed to hydrographs, applying the Beta distribution function. Synthetic floods are routed through a reservoir to assess the risk of overtopping a dam. The resulting maximum water levels are compared to estimations considering the peak flow and volume separately. The analysis is performed using daily flows observed in the River Agrio in Neuquén Province, Argentina, a catchment area of 7300 km². The bivariate approach results in higher maximum water level values. Therefore the multivariate approach should be preferred for the estimation of design variables.

Editor D. Koutsoyiannis; Associate editor S. Grimaldi     

人工合成锆石Lu-Hf同位素标样方法研究

研究了人工合成锆石并加入微量元素的实验方法和条件。人工合成锆石是以氧化锆和硅酸锂为原料,以钼酸锂和氧化钼为助熔剂,并加入其他元素如Hf、Lu、Yb、U、Th、Pb等元素,充分混匀后转入带盖铂金坩埚中,在高温马弗炉中连续加热生长形成锆石晶体。利用激光剥蚀系统与电感耦合等离子体质谱技术分析了合成锆石晶体中微量元素含量和Lu-Hf同位素组成,结果表明合成锆石晶体中Lu、Yb、U、Th、Pb等微量元素含量不均一,而Hf的含量和Lu-Hf同位素组成有很好的均一性。     

2011年大理州入汛后首场区域性大雨过程分析

分析2011年6月27～28日大理地区人汛来首场强降水天气过程的影响系统、物理量特征以及风廓线雷达资料,结果表明此次区域性强降水过程的主要影响系统是东移的中纬度槽和低层的切变线;区域性强降水开始前,大理上空是不稳定能量的密集区且大气处层结于不稳定状态;从水汽条件看,过程开始前低层湿度虽大,但没有水汽的强辐合;强降水出现时存在剧烈的上升运动释放不稳定能量,且低层正涡度高层负涡度,散度场上低层辐合高层辐散,但低层辐合并不强;信噪比和垂直速度在降水的持续时间和降水强度方面与降水对应关系非常密切,强降水出现时间及持续时间与40dbz高信噪比出现时间一致,垂直速度负值绝对值越大降水越强,厚度越厚持续时间越长;强降水出现时水平风随高度存在多层切变,强降水出现期间水平风矢量达到最高的位置,随着降水的减弱,测量到的水平风矢量高度明显降低。     

风廓线雷达与多普勒天气雷达风矢产品对比及相关分析

利用成都地区2010年8月和北京沙河地区2011年7—8月风廓线雷达以及多普勒天气雷达的风廓线探测资料,结合对应时段的天气现象相关记录,通过对比分析得到以下结论:①弱降水条件下,在300~2100m高度内,风廓线雷达与多普勒天气雷达探测具有很好的相关性,风向相关系数平均值为0.596,风速相关系数平均值为0.736,在做预报时两者可以同时应用,互为补充;②强降水天气条件下,风廓线雷达与多普勒天气雷达探测的风向、风速变化趋势基本一致,特别是在300~2100m之间各个高度上风向、风速相关性较好,风向相关系数平均值为0.573,风速相关系数为0.508,且风廓线雷达比多普勒天气雷达探测到的各层风向、风速变化更为详细、直观;③阴天条件下风廓线雷达与多普勒天气雷达的风向、风速相关性低层比高层好;④晴天条件下,风廓线雷达更适合用于预报和监测天气。     

Mixing regimes in the equatorial crater lakes of western Uganda

In order to understand the ecological functioning of lake ecosystems, little is more crucial than knowledge of their mixing regime. However in tropical regions, this information is scarce for all except the largest lakes, and often inferred from occasional observation of physical water-column properties. In this study, a total of 276 water-column profiles of temperature, conductivity and dissolved oxygen collected between 2000 and 2017 in 60 volcanic crater lakes in equatorial western Uganda are used to classify these lakes according to mixing regime. Most study lakes are small (on average 29 ha), but together they cover a spectacularly large gradient in maximum depth (Z_max) between 1.4 m and > 220 m, and consequently they display a wide range of mixing regimes. We identified four lakes as continuous warm polymictic, 12 as discontinuous warm polymictic, and 11 other lakes mix completely once or twice each year. We classify these 11 lakes as equatorial dimictic, because they experience deep mixing during both dry seasons separated by long periods of stable stratification, while the season of complete mixing may differ between years and among neighbouring lakes. The 33 remaining lakes do not usually mix completely and are thus meromictic. Relative depth (Z_r) is the main factor controlling the mixing regime of these lakes. The presence of a shallow permanent chemocline reduces mixing depth, and the smallest meromictic lakes (< 3 ha) tend to occasionally mix deeper than predicted by Z_r. Based on these variables, predictions can be made about the mixing dynamics of Ugandan crater lakes not covered by our dataset. Previous suggestions that the mixing depth of tropical crater lakes is strongly influenced by the wind shelter provided by a high crater rim or by water-column transparency could not be confirmed.