Conservative identification of nodal transmissivities: theory,computational experiments and application to the Rharb coastal aquifer (Morocco)

Abstract

In order to calculate the transmissivity from the inverse problem corresponding to the groundwater flow in an isotropic horizontal aquifer, a numerical conservative approach is tested. The method deals with triangulation of the domain and applies the conservation of mass to elements of the mesh using the harmonic mean for internodal transmissivities. An optimal sweeping algorithm is used to evaluate nodal transmissivities from one element to another with a minimal relative error accumulation. The practical importance of the method is demonstrated through two synthetic examples representing those experienced in the field, then through application to a Moroccan aquifer. The computed hydraulic head is well fitted to the reference one, which confirms the validity of the identified transmissivity model.     

Modeling visibility through vegetation

The calculation of visibility patterns associated with past monuments and sites is an important element in modern landscape archaeology. These types of investigations have been limited by the inability of current viewshed routines to incorporate vegetation information. The following paper presents a new viewshed algorithm aimed at calculating the probability of locations being visible in the presence of vegetation. To this day, little work has been done to address this limitation, a notable exception is Dean's Permeability Index Model (1997 Dean, D. J. 1997. Improving the accuracy of forest viewsheds using triangulated networks and the visual permeability method.. Canadian Journal of Forest Research, 27: 969–977. [Crossref] , [Google Scholar]). A review of Dean's model is provided here in the light of the new proposed algorithm. The new algorithm is based on mathematical principles found in Beer–Lambert's Attenuation Law, a physics law governing the attenuation of light through a medium. In addition to common viewshed parameters, the routine requires a 3D model of a tree/plant and a layer indicating the spatial distribution and density of vegetation on the landscape. The possibility of varying both, the spatial and density distribution of tree/plants, and the three‐dimensional model representing vegetation makes the model well suited to investigate the impact that vegetation may have on visibility patterns.     

Cenozoic erosion and flexural isostasy of Scandinavia

The presence of Cenozoic deposits along the Norwegian Atlantic margin required extensive erosion of the Scandinavian Mountains in a generally cooling climate from the Oligocene to the present. The volume of the deposits implies that the transfer of mass from the inland area to the offshore shelf induced isostatic displacements on a kilometer scale. However, except for glacial excavation of the deep fjords, little is known about the distribution of Cenozoic inland erosion. A long-lasting paradigm incorporates remnants of peneplains at high elevation and assumes very little Cenozoic erosion on these surfaces through time. This scenario has recently been challenged by quantitative geomorphological studies indicating that the matrix of Cenozoic sediments deposited offshore must have been sourced from these surfaces. An alternative explanation for the present-day high-elevation low-relief surfaces is therefore that they evolved throughout the Cenozoic because of glacial and periglacial erosion processes that are known to vary strongly with altitude. Here we explore the implications of the latter scenario by reconstructing a pre-Cenozoic fluvial landscape without elevated low-relief surfaces. We use the present-day offshore sediment volumes for constraining the total Cenozoic erosion, and we find that a likely pre-Cenozoic fluvial landscape is only in few places more than 1 km higher than today. The rock mass of the offshore sediments is generally used for filling the fjords created during the Quaternary glaciations and for restoring concave river profiles from sea level to the peaks. Our reconstruction is based on a fluvial landscape algorithm and considers the isostatic response to the transfer of rock mass – from the basins onto the onshore area. A comparison between the reconstructed and the present-day topography demonstrates that offshore tilting of pre-Cenozoic strata can be partly explained by flexural isostatic compensation in response to the Cenozoic erosion and deposition. Locations of future thermochronometry studies for testing Scandinavian landscape evolution models are suggested based on temperature estimates of the present-day surface buried beneath the erosion products restored from the offshore basins.     

Relative pollen productivities of the major plant taxa of subtropical evergreen–deciduous mixed woodland in China

Quantifying the relationship between pollen and vegetation is an essential step in the pollen-based quantitative reconstruction of past vegetation cover. In this study, we use the Extended R-Value (ERV) model and a modern dataset of pollen (collected from moss polsters) and related vegetation from 50 sites in the Daba Mountains (subtropical China) to (i) estimate the relevant source area of pollen (RSAP) of the moss samples and the relative pollen productivities (RPPs) of nine major plant taxa-characteristic of the region, and (ii) evaluate the obtained RPPs. The RSAP estimates of moss polsters vary between 225 and 610 m depending on the ERV submodels and models of pollen dispersal and deposition used. The RPP estimates are different from values published in previous studies from temperate and subtropical China. This may be explained by differences in methodology, climate and vegetation (species composition and spatial distribution), of which vegetation is probably the most important factor. The ranking of the RPP estimates for the nine taxa is Pinus > Juglandaceae > D − Quercus (deciduous Quercus) > Poaceae > Rosaceae > Cyperaceae > Anacardiaceae > Castanea > Fabaceae. We use a ‘leave-one-out’ cross-validation strategy and the Landscape Reconstruction Algorithm (LRA) for pollen-based reconstruction of regional and local plant cover to evaluate the ERV model-based RPP estimates. Both the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites)-based and the LOVE (LOcal Vegetation Estimates)-based plant cover using the RPP estimates are closer to the modern vegetation composition than pollen percentages, thus confirming the applicability of the ERV model and the LRA approach in subtropical China.     

3维重构精度估计的矩阵分析方法

3维重构可以由影像序列快捷方便地提取目标的3维几何信息.但3维重构的基础是多视几何理论,其计算是基于矩阵推导的非线性过程,故传统摄影测量理论难以用于评估其误差,本文提出一种3维重构精度的估计方法,采用矩阵分析方法,给出了评定重构精度的推导过程,并结合实验数据验证了精度估计的正确性.     

青岛市城中村土地征用(收)调查

随着全国大部分地区尤其是东部沿海区域城市化发展进入加速期,城区土地资源紧张问题愈发显现。同时城区内大片旧城区和城中村的改造,影响着城市化能否顺利实施,为了破解这一城市发展难题,青岛市国土部门创新思路,探索实施新的城中村土地征用(收)办法,全方位保障被拆迁群众的利益,推动了城市化的顺利实施,促进了社会的和谐和城市经济健康发展。     

Establishment of tree-ring chronology and climatic response of Tibetan juniper (S. tibetica) in south Tibet, western China

A tree-ring width chronology of 442 years(1567-2008) was developed from Tibetan junipers(S.tibetica) derived from south Tibet in western China.Three versions of chronology were produced according to standard dendrochronological techniques.The correlation and response analysis displays a high correlation between the standard tree ring-width chronology and observed annual mean precipitation series during the period 1961-2008.Based on a linear regression model,an annual(prior August to current July) precipitation for the past 229 years was reconstructed.This is the first well-calibrated precipitation reconstruction for the Nanggarze region,south Tibet.The results show that relatively wet years with above-average precipitation occurred in 1780-1807,1854-1866,1886-1898,1904-1949,1967-1981 and 2000-2008,whereas relatively dry years with below-average precipitation prevailed during 1808-1853,1867-1885,1899-1903,1950-1966 and 1982-1999.Common dry/wet periods during 1890s,1910s,1940s-1960s and 1980s were also identified from other moisture reconstructions of nearby regions,indicating a synchronous climatic variation in south Tibet.Abrupt change beginning in 1888 was detected,revealing a transition from wet to dry conditions in south Tibet.Power spectrum analysis reveals significant cycles of 28-year,5.5-5.6-year and 3.3-year during the past 200 years.     

最小加权范数插值与调制升频结合的地震数据重建研究

提出一种新的反假频地震数据重建的两步算法,将最小加权范数插值(MWNI)方法与调制升频方法有效地结合起来.首先利用MWNI方法构建数据谱的低频部分,为了提高计算效率,在低频重建算法中,引入了预条件共轭梯度法求解反问题方程,并使用了与频率有关的变波数带宽技术;然后,基于重建的低频数据,采用调制升频方法重构数据的高频部分.调制升频方法灵活,简便,能有效地从低频资料中恢复出高频成分,克服了以往AR模型预测高频走不远的限制,当数据存在严重的空间假频时,亦能获得较好的重建效果.该两步算法不仅可用于规则地震数据的内插重建,也可用于含空道地震数据的重建.理论模型和实际地震数据重建试验表明,该方法效率高,精度高,反假频能力强,重建剖面波形连续、自然,与正确完整的地震剖面相似程度高,具有良好的实用价值和应用前景.     

Comparison of methods for integrating biological and physical data for marine habitat mapping and classification

An important first step in marine spatial planning and ecosystem-based management efforts is the creation of benthic habitat maps that allow scientists and managers to understand the distribution of living and non-living resources on the seafloor. However, the location of boundaries between and composition of habitats is highly dependent on the approach taken to integrate abiotic and biotic information. The purpose of this study was to test “top-down” and “bottom-up” approaches for integrating physical and biological data derived from commonly used sub-tidal benthic mapping tools to create a habitat map compatible with the US Coastal and Marine Ecological Classification Standard (CMECS). We found that a top-down framework, where we tested for differences in macrofauna assemblages among side scan sonar facies, defined two broad-scale and general habitats. Using the bottom-up approach, where patterns in abiotic and biotic variables were examined with multivariate statistics (BEST, LINKTREE, ANOSIM, SIMPER), we generated seven biotopes based on the macrofauna abundance, percent sand, water depth, and backscatter standard deviation that corresponded well to, but provided more fine-scale detail than the top-down habitats. We were able to use the statistical relationship between abiotic variables and macrofauna assemblages in the LINKTREE to predict the spatial distribution of assemblages over ∼50% of the study area. We created a local catalogue of biotopes specific to our study area that contributes to the CMECS library. In addition, we were able to fully map CMECS Geoform, Surface Geology, and Biotic Cover Components. This mapping effort represented real progress toward reconciling the “data density mismatch” between physical and biological mapping methods, and it provided further evidence that using a bottom-up methodology preserves species–environment relationships.     

基于POCS方法指数阈值模型的不规则地震数据重建(英文)

不规则地震数据会对地震多道处理技术的正确运行造成不良影响,降低地震资料的处理质量。本文将广泛用于图形图像重建的凸集投影方法应用到地震数据重建领域,实现规则样不规则道缺失数据的插值重建。对于整道缺失地震数据,将POCS迭代重建过程由时间域转移到频率域实现,避免每次迭代都对时间做正反Fourier变换,节约了计算量。在迭代过程中,阈值参数的选择方式对重建效率有重要影响。本文设计了两种阈值集合模型进行重建试验,试验结果表明:在相同重建效果下,指数型阈值集合模型可以有效减少迭代次数,提高重建效率。此外,分析了POCS重建方法的抗噪性能和抗假频性能。最后,理论模型和实际资料处理效果验证了本文重建方法的正确性和有效性。