Incorporating spatial interaction patterns in classifying and understanding urban land use

Land use classification has benefited from the emerging big data, such as mobile phone records and taxi trajectories. Temporal activity variations derived from these data have been used to interpret and understand the land use of parcels from the perspective of social functions, complementing the outcome of traditional remote sensing methods. However, spatial interaction patterns between parcels, which could depict land uses from a perspective of connections, have rarely been examined and analysed. To leverage spatial interaction information contained in the above-mentioned massive data sets, we propose a novel unsupervised land use classification method with a new type of place signature. Based on the observation that spatial interaction patterns between places of two specific land uses are similar, the new place signature improves land use classification by trading off between aggregated temporal activity variations and detailed spatial interactions among places. The method is validated with a case study using taxi trip data from Shanghai.     

Optimizing precipitation station location: a case study of the Jinsha River Basin

Precipitation stations are important components of a hydrological monitoring network. Given their critical role in rainfall forecasting and flood warnings, along with limited observation resources, determining the optimal locations to deploy precipitation stations presents an important problem. In this paper, we use a maximal covering location problem to identify the best precipitation station sites. Considering the terrain conditions and the characteristics of a rainfall network, the original maximal covering location model is modified with the introduction of a set of additional constraints. The minimum density requirement is used to determine a precipitation station’s coverage range, and three weighting schemes are used to evaluate each demand object’s covering priority. As a typical mountainous watershed with high annual precipitation, the Jinsha River Basin is selected as the study area to test the applicability of the proposed method. Results show that the proposed method is effective for precipitation station configuration optimization, and the model solution achieves higher coverage than the real-world deployment. Compared with the commercial solver CPLEX, a genetic algorithm-based heuristic can significantly reduce the computation time when the problem size is large. Several deployment strategies are also discussed for establishing the optimal configuration of precipitation stations.     

高密度电法在工程地质中的应用二例

硅灰石矿和水库工程地质中应用高密度电阻率法,资料数据处理快捷准确,推测拟断面成果可靠。     

竺可桢先生对气候变迁研究的贡献

1972年,竺可桢先生发表了《中国近五千年来气候变迁的初步研究》著名论文。这是他在文化革命动乱年代发表的唯一的论文,也是他的最后一篇论文,然而却又是他最为光彩影响最大的学术论文之一。竺可桢先生在一九六六年就写成了《中国近五千年来气候变迁的初步研究》初稿,并在他参加的罗马尼亚科学院一百周年纪念会上散发。回国后,他又进一步补充、修改。     

The effects of land surface process perturbations in a global ensemble forecast system

Atmospheric variability is driven not only by internal dynamics, but also by external forcing, such as soil states, SST, snow, sea-ice cover, and so on. To investigate the forecast uncertainties and effects of land surface processes on numerical weather prediction, we added modules to perturb soil moisture and soil temperature into NCEP’s Global Ensemble Forecast System (GEFS), and compared the results of a set of experiments involving different configurations of land surface and atmospheric perturbation. It was found that uncertainties in different soil layers varied due to the multiple timescales of interactions between land surface and atmospheric processes. Perturbations of the soil moisture and soil temperature at the land surface changed sensible and latent heat flux obviously, as compared to the less or indirect land surface perturbation experiment from the day-to-day forecasts. Soil state perturbations led to greater variation in surface heat fluxes that transferred to the upper troposphere, thus reflecting interactions and the response to atmospheric external forcing. Various verification scores were calculated in this study. The results indicated that taking the uncertainties of land surface processes into account in GEFS could contribute a slight improvement in forecast skill in terms of resolution and reliability, a noticeable reduction in forecast error, as well as an increase in ensemble spread in an under-dispersive system. This paper provides a preliminary evaluation of the effects of land surface processes on predictability. Further research using more complex and suitable methods is needed to fully explore our understanding in this area.     

基于FY-3/MERSI数据的北冰洋流冰自动提取与跟踪方法

北冰洋航路是未来全球航运的重点开拓领域,海冰运动对北冰洋航路开发有重要影响。本文利用风云三号卫星中分辨率光谱成像仪(FY-3/MERSI)数据的特点和优势,研究北冰洋流冰自动提取和运动跟踪的方法。首先在分析流冰灰度分布特征的基础上,提出分区域阈值分割与梯度差分相结合的方法实现块状流冰提取,然后根据块状流冰的多种几何特征匹配同名流冰并计算其运动速度。应用这种方法跟踪2011年6月弗雷姆海峡流冰运动,跟踪结果与美国国家冰雪数据中心提供的极地网格化日均海冰运动矢量整体趋势一致,验证了方法的有效性。这种方法获取各块流冰实际运动速度,可以有效弥补网格化海冰运动平均速度场分布和细节的不足,为北冰洋航路开发提供更详细的流冰运动信息。     

希尔伯特-黄变换在微弱被动瞬态鱼声信号中的检测

为了在海洋环境中准确获取鱼类在摄食、产卵和争斗过程中发出的短促、瞬时的信号,采用希尔伯特-黄变换算法实现微弱被动瞬态鱼声信号的检测。该算法首先将瞬态鱼声信号实现固有模态信号的分解,其次将经验值高阶阶数的固有模态信号求和重构即可实现信号能量幅度检测;在固有模态信号的分解的基础上,计算求和重构信号的希尔伯特能量谱,即可实现瞬时能量密度级的检测。通过不同信噪比和检测器的比较研究,结果表明基于希尔伯特-黄变换算法的两种检测方法能有效提高微弱被动瞬态鱼声信号的检测性能。     

Inferring trip purposes and uncovering travel patterns from taxi trajectory data

Global positioning system-enabled vehicles provide an efficient way to obtain large quantities of movement data for individuals. However, the raw data usually lack activity information, which is highly valuable for a range of applications and services. This study provides a novel and practical framework for inferring the trip purposes of taxi passengers such that the semantics of taxi trajectory data can be enriched. The probability of points of interest to be visited is modeled by Bayes’ rules, which take both spatial and temporal constraints into consideration. Combining this approach with Monte Carlo simulations, we conduct a study on Shanghai taxi trajectory data. Our results closely approximate the residents’ travel survey data in Shanghai. Furthermore, we reveal the spatiotemporal characteristics of nine daily activity types based on inference results, including their temporal regularities, spatial dynamics, and distributions of trip lengths and directions. In the era of big data, we encounter the dilemma of “trajectory data rich but activity information poor” when investigating human movements from various data sources. This study presents a promising step toward mining abundant activity information from individuals’ trajectories.     

An improved topographic correction model based on Minnaert

The uneven distribution of solar radiation due to topographic relief can significantly change the correlation between reflectance and other features such as biomass in rugged terrain regions. In this article, we use the transfer theory to improve the Minnaert approach. After comparing topographic correction methods for Landsat 8 Operational Land Imager (OLI) and EO-1 Advanced Land Imager (ALI) imagery acquired from the mountainous region in Beijing, China, we used visual inspection, statistical analysis, and correlation analysis to evaluate the algorithms and performance of the proposed Minnaert-E approach. The results indicate that corrections based on non-Lambertian methods have better performance than those based on the Lambertian assumption. The correction performances can be ranked as the Minnaert-E, followed by the Minnaert and the SCS+C corrections, and, finally, the C-HuangWei correction, which performed the worst. We found that the Minnaert-E approach can effectively weaken the influence of terrain relief on pixels and restore the true reflectance of the pixels in the relief area. Further analysis indicates that the Minnaert-E has a better effect on image processing where the slope gradient is restricted to less than 10° or between 30° and 43°.     

东北哈尼泥炭沼泽中酚酸的组成、酚铁相互作用及其环境意义

大量研究表明,溶解性有机质与铁的螯合对生物可利用性铁的输出有重要影响.然而,对于天然有机质,尤其是泥炭沼泽源的酚类物质,与铁相互作用的地球化学机制仍然缺乏研究.以长白山西麓哈尼泥炭沼泽为研究对象,调查了泥炭沼泽源水体可溶性总铁、亚铁、水溶性总酚等理化指标.同时,测定了泥炭中酚酸的组成及含量,分析对比泥炭与土壤中铁的主要赋存形态.并开展了酚铁相互作用模拟实验,研究了泥炭沼泽源水体中酚铁相互作用机制.结果表明:哈尼泥炭沼泽水体中亚铁浓度与水溶性总酚浓度显著相关,说明水溶性总酚对亚铁的存在及运移有重要影响.哈尼泥炭中含有原儿茶酸、咖啡酸、没食子酸、龙胆酸、丁香酸、阿魏酸、对羟基苯甲酸、对香豆酸、水杨酸、香草酸等多种酚酸.其中,具有儿茶酚或没食子酰基结构的原儿茶酸、咖啡酸和没食子酸能与亚铁形成稳定螯合物,是泥炭沼泽源水体中Fe(Ⅱ)保持稳定并可以远距离迁移的关键.研究还表明,原儿茶酸、咖啡酸、没食子酸和龙胆酸对Fe(Ⅲ)有显着的还原作用,有利于沼泽区水体中的保持较高Fe(Ⅲ)和Fe(Ⅱ)浓度.哈尼泥炭中铁主要以活动态(可交换态、络合态和无定形态)为主,为铁的迁移、转化和循环奠定了基础.鉴于泥炭沼泽在全球的分布面积巨大以及亚铁对海洋生物有促进作用,酚酸对铁的作用机制对陆地系统向海洋输送生物可利用铁具有重要意义,并对碳循环、硫循环以及气候变化有重要影响.