Permeability of compacted granule–clay mixtures

Achieving a sufficiently low permeability for the aggregate-clay mixtures, whether used as the core of embankment dam or soil liner, is essential. The study illustrates the role of granule (bead or aggregate) content and size, confining stress and fabric anisotropy on the permeability of ceramic bead–lean clay and aggregate-fat clay mixtures. It is shown that depending on the plasticity of the clay, the permeability may decrease or increase with bead/aggregate content. The permeability also decreases when either granule size or confining stress increases. It is found that the permeability is affected by fabric anisotropy in such a manner that its value in the horizontal direction (k_h) is more than that in the vertical direction (k_v), however, k_h/k_v decreases towards 1 for bead contents equal to or below 40%. In high bead content mixtures (i.e., 60% beads) k_h/k_v reaches as high as 3 with an increase in the confining stress. The concept of the development of heterogeneous field of density in the clay is also used to demonstrate the impact of granule size and fabric anisotropy on the permeability.     

Catchment scale spatial variability of soil salt content in agricultural oasis,Northwest China

Soil salinization is a serious environmental problem in the world, especially in arid and semi-arid regions. Therefore, estimating spatial variability of soil salinity plays an important role in environmental sciences. Aiming at the problem of soil salinization inside an oasis, a case study was carried out at the Sangong River catchment in Xinjiang province, northwest China. Methods of classical statistics, geostatistics, remote sensing (RS) and geographic information system (GIS) were applied to estimate the spatial variability of soil salt content in the topsoil (0–20 cm) and its relationship with landscape structure at catchment scale. The objective of this study was to provide a scientific basis to understand the heterogeneous of spatial distribution of soil salt content at a large scale. The results revealed that (1) elevation of landform was a key factor for soil salt content’s spatial variability, and soil salt content had a strong spatial autocorrelation, which was mainly induced by structural factors. (2) Mapping of soil salt content by Kriging and comparing it with landscape maps showed that area of soil salinization in old oasis was smaller than that in new oasis, and degree of soil salinization in old oasis was also lower than that in the new one. Among all landscapes, cropland was mostly affected by salinity, with 38.8% of the cropland in new oasis moderately affected by soil salinity, and 8.54% in old oasis.     

The variation of soil temperature and water content of seasonal frozen soil with different vegetation coverage in the headwater region of the Yellow River, China

The variation and distribution of temperature and water moisture in the seasonal frozen soil is an important factor in the study of both the soil water cycle and heat balance within the source region of the Yellow River, especially under the different conditions of vegetation coverage. In this study, the impact of various degrees of vegetation coverage on soil water content and temperature was assessed. Soil moisture (θ _v) and soil temperature (T _s) were monitored on a daily basis. Measurements were made under different vegetation coverage (95, 70–80, 40–50 and 10%) and on both thawed and frozen soils. Contour charts of T _s and θ _v as well as a θ _v–T _s coupling model were developed in order to account for the influence of vegetation cover and the interaction between T _s and θ _v. It was observed that soil water content affected both the overall range and trend in the soil temperature. The regression analysis of θ _v versus T _s plots indicated that the soil freezing and thawing processes were significantly affected by vegetation cover changes. Vegetation coverage changes also caused variations in the θ _v–T _s interaction. The effect of soil water content on soil temperature during the freezing period was larger than during the thawing period. Moreover, the soil with higher vegetation coverage retained more water than that with lower coverage. In the process of freezing, the higher vegetation coverage reduced the rate of the reduction in the soil temperature because the thermal capacity of water is higher than that of soil. Areas with higher vegetation coverage also functioned better for the purpose of heat-insulating. This phenomenon may thus play an important role in the environmental protection and effective uses of frozen soil.     

应用型本科院校“摄影测量学”教学改革探讨

针对"摄影测量学"课程内容丰富且理论抽象、课时数有限,以及当前应用型本科院校"摄影测量学"课程教学中存在的实验内容单一、考核形式欠科学等问题,从优化教学内容、丰富教学手段、创新教学模式以及改进考核方式等方面逐步实现"摄影测量学"课程的教学改革。结果表明,通过课程改革可激发学生的学习兴趣,增强学生分析和解决实际工程问题的能力,学生综合素质得到提高,取得较好的教学效果。     

基于landsat 8-OLI/TIRS和HJ-1B太湖叶绿素含量和温度反演研究

水体的表面温度是研究环境气候变化的一个重要参数,同时,也是研究生物物理过程的一个不可或缺的因子。卫星遥感对大面积水体表面温度的监测有着传统的测量手段无法比拟的效率。水体表面的温度变化不仅对水中生物的生存有着重要的意义,同时,水温的变化也常常会导致水中浮游生物和植物疯长,进而引起水资源的污染,对人们的生活造成严重的影响。本文利用ENVI/IDL 5.1对Landsat 8卫星的OLI/TIRS数据和HJ-1CCD多光谱数据在太湖水体区域开展了其在温度反演和叶绿素含量的监测等领域的研究。研究结果表明:1)使用HJ_1B反演的结果和Landsat 8反演的结果呈现一致性。2)通过实测的数据和反演数据建立了模型并通过同名点实测数据对实验结果进行了验证,证明了建立的模型的可靠性,找到了误差来源。最后分析了造成叶绿素含量较高的原因及反演的难点。     

Deriving incline values for street networks from voluntarily collected GPS traces

ABSTRACT

When producing optimal routes through an environment, considering the incline of surfaces can be of great benefit in a number of use cases. For instance, steep segments need to be avoided for energy-efficient routes and for routes that are suitable for mobility-restricted people. Such incline information may be derived from digital elevation models (DEMs). However, the corresponding data capturing methods (e.g. airborne LiDAR, photogrammetry, and terrestrial surveying) are expensive. Current low-cost and open-licensed DEM (e.g. Shuttle Radar Topography Mission [SRTM] and Advanced Spaceborne Thermal Emission and Reflection Radiometer [ASTER]) generally do not have sufficient horizontal resolution or vertical accuracy, and lack a global coverage. Therefore, we have investigated an alternative low-cost approach which derives street incline values from GPS traces that have been voluntarily collected by the OpenStreetMap contributors. Despite the poor absolute accuracy of this data, the relative accuracy of traces seems to be sufficient enough to compute incline values with reasonable accuracy. A validation shows that the accuracy of incline values calculated from GPS traces slightly outperforms incline values derived from SRTM-1 DEM, though results depend on how many traces per street segment are used for computation.     

Crowdsourcing a cyclist perspective on suggested recreational paths in real-world networks

ABSTRACT

Routing and navigation services for leisure activities are conditioned by special needs and trade-offs. The advent of online communities and large crowdsourced datasets offers opportunities to improve the adoption of a user’s perspective in these suggested paths. This paper focuses on achieving two goals. First, the presented methodology analyses a dataset of 190,610 historical GPS traces to gain insights into the appreciation or attractiveness of each edge in a real-world network for a specific leisure activity (i.e. road cycling). Second, as literature on these leisure activities is still sparse, we want to create a thorough understanding of the activities at hand for future work. An appreciation model is proposed and the spread of this score is analyzed in shortest-path alternatives of popular routing engines for this activity. This analysis successfully discriminates these shortest paths based on the scoring value and three morphological parameters of the path. However, the robustness of the model should be improved to ensure the viability of the proposed approach in future work. More specifically, further research on the local optimality of the route choices will be imperative.     

The interaction between individual,social and environmental factors and their influence on dietary intake among adults in Toronto

Health outcomes related to vegetable and fruit consumption are widely recognized in the literature. This study investigates how dietary intake is influenced by individual, social, and environmental factors in the Toronto Census Metropolitan Area. The analysis and findings are based on data from the Canadian Community Health Survey which provides self‐reported vegetable and fruit intake from 6,513 adults in 2009‐2010. Food environment measures were constructed from commercial databases using kernel density estimates and network drive times. Spatial and multivariable techniques were used to determine the associations between diet, the food environment, and other health and socioeconomic factors. Particular emphasis was given to understanding the interaction between the food environment and socioeconomic position. Unexpectedly, supermarket density was found to have an inverse association with vegetable and fruit intake. Interaction terms for individuals with low income and reduced mobility produced different responses in men and women, confirming that the influence of the food environment is not uniform for all subgroups.     

Completeness of citizen science biodiversity data from a volunteered geographic information perspective

Observations of living organisms by citizen scientists that are reported to online portals are a valuable source of information. They are also a special kind of volunteered geographic information (VGI). VGI data have issues of completeness, which arise from biases caused by the opportunistic nature of the data collection process. We examined the completeness of bird species represented in citizen science observation data from eBird and iNaturalist in US National Parks (NPs). We used approaches for completeness estimation which were developed for data from OpenStreetMap, a crowdsourced map of the world. First, we used an extrinsic approach, comparing species lists from citizen science data with National Park Service lists. Second, we examined two intrinsic approaches using total observation numbers in NPs and the development of the number of new species being added to the data-set over time. Results from the extrinsic approach provided appropriate completeness estimations to evaluate the intrinsic approaches. We found that total observation numbers are a good estimator of species completeness of citizen science data from US NPs. There is also a close relationship between species completeness and the ratio of new species added to observation data vs. observation numbers in a given year.     

土壤水分观测历史数据集奇异值分析与校正

针对中国247个农业气象土壤水分观测站点1981 2010年逐旬土壤重量含水量、逐年田间持水量、凋萎湿度和土壤容重,考虑地区气候特点和土壤质地,依据土壤水分极值和水文常数关系理论,制定了土壤水分观测历史数据集质量控制方法,对土壤水分数据奇异值进行分析与校正。结果表明:土壤水分观测历史资料中,奇异值问题可以归结为人工录入误差、多地段水文常数混用误差和年际变化异常;土壤重量含水量数据异常问题归结为小于风干土含水量和大于理论饱和含水量的极端情况。通过对历史数据集质量控制后,可以对土壤水分观测数据进行有效推广应用,为针对土壤水分的研究提供重要科学基础。