基于遥感和机器学习的内陆水体水深反演技术

文章主要根据机器学习算法（随机森林算法和极端梯度提升算法）和遥感水深反演的原理,利用Sentinel_2多光谱卫星数据和无人船实测水深数据,对内陆水体——梅州水库建立了随机森林（RF）、极端梯度提升（XGBoost）和支持向量机（SVM）水深反演模型,并对反演结果进行对比分析。结果表明：1）RF的训练精度为97%,测试精度为0.80;XGBoost模型的训练精度为97%,测试精度为0.79;SVM的训练精度为90%,测试精度为0.78。说明了在水深预测方面RF模型和XGBoost模型比SVM模型表现更好,对各个区段的水深值较为敏感。2）根据运行时间考察各个模型的效率,其中RF模型从读取数据至输出结果耗时3.92 s;XGBoost模型4.26 s;SVM模型6.66 s。因此,在反演精度和效率上RF模型优于XGBoost模型优于SVM模型,且RF模型的预测结果图细节更加丰富,轮廓更加分明;XGBoost模型次之,但总体效果也较好;SVM模型表现最差。由此可知,机器学习水深反演模型获得的水深结果精度明显提高,解决了传统水深反演模型精度不高的问题。     

基于XGBoost的多源降水数据融合方法研究

气象站点观测降水难以精确反映降水时空分布与变化,而雷达降水存在复杂地形区域精度不高等问题。为了最大限度发挥两者的优势,文章以广东省北部山区为研究区域,选择2018-08-26—30一次暴雨过程为研究对象,结合地形、与海岸线距离、植被指数、经纬度等地表辅助参量,分析地面站点降水与地表辅助参量、雷达降水的相关关系,利用XGBoost算法与克里金插值方法,构建地面-雷达日降水数据融合模型,得到了空间分辨率为1 km的日降水融合数据集。此外,采用多元线性回归（LM）与克里金插值方法,实现了地面-雷达日降水数据的融合,并利用地面降水数据分别对XGBoost与LM日降水融合性能进行精度验证。结果表明：1）地面降水与雷达降水存在显著的正相关,地面降水与地表辅助参量之间的相关性随时间变化;2）XGBoost预测精度整体上高于LM预测结果;经模型残差校正后,XGBoost融合模型的精度整体上优于LM融合模型,这是因为XGBoost方法在捕捉地面降水与地表辅助参量、雷达降水之间关系性能上优于LM方法。     

建成环境与青少年步行通学的非线性关系——基于极限梯度提升模型的研究

步行不仅是一种原始、便捷的交通方式,同时也是体力活动的重要组成部分,对于提升公共健康、改善交通拥堵和减轻污染排放等均有重要的积极意义。然而,包括青少年在内的城市居民步行比例持续下降,体力活动水平日益降低。青少年正处于身心发育的关键时期,体力活动的缺乏将导致肥胖等慢性非传染病,为其将来发展埋下巨大的健康隐患。如何通过对建成环境进行干预,提高青少年步行通学比例,从而提高其体力活动水平,引起了不少学者的关注,取得了较为丰硕的研究成果。然而,既有研究存在以下不足：第一,大部分已有研究以西方城市为案例,很少研究关注中国城市;第二,绝大部分既有研究基于线性或广义线性的假设考察建成环境对步行通学的影响,很少研究关注两者之间的非线性关系。鉴于此,论文以厦门岛为案例,基于极限梯度提升模型,考察青少年家和学校建成环境对其步行通学的影响。研究发现：① 通学距离是影响青少年步行通学最重要的因素,其相对贡献接近4成(39.99%);② 建成环境(以5Ds模型表征)作用显著,家、校建成环境相对贡献合计达36.28%,超过社会经济属性(23.73%),离市中心的距离和道路交叉口密度等变量具有重要作用;③ 全部建成环境变量和主要社会经济属性变量均与青少年步行上学存在非线性关系,且存在明显的阈值效应。研究为城市决策者关于提高青少年步行通学倾向提供了丰富的政策启示。     

Unsupervised regionalization of the United States into landscape pattern types

We present a pattern-based regionalization of the conterminous US – a partitioning of the country into a number of mutually exclusive and exhaustive regions that maximizes the intra-region stationarity of land cover patterns and inter-region disparity between those patterns. The result is a discretization of the land surface into a number of landscape pattern types (LPTs) – spatial units each containing a unique quasi-stationary pattern of land cover classes. To achieve this goal, we use a recently developed method which utilizes machine vision techniques. First, the entire National Land Cover Dataset (NLCD) is partitioned into a grid of square-size blocks of cells, called motifels. The size of a motifel defines the spatial scale of a local landscape. The land cover classes of cells within a motifel form a local landscape pattern which is mathematically represented by a histogram of co-occurrence features. Using the Jensen–Shannon divergence as a dissimilarity function between patterns we group the motifels into several LPTs. The grouping procedure consists of two phases. First, the grid of motifels is partitioned spatially using a region-growing segmentation algorithm. Then, the resulting segments of this grid, each represented by its medoid, are clustered using a hierarchical algorithm with Ward’s linkage. The broad-extent maps of progressively more generalized LPTs resulting from this procedure are shown and discussed. Our delineated LPTs agree well with the perceptual patterns seen in the NLCD map.     

树轮资料(1511～1954)太阳活动的多尺度分析——EMD方法的应用

用EMD对Stu iver等提供的树轮14C资料进行分析,结果为:①得到太阳活动的准3、6、11、22、44、110、200、300 a的周期;从趋势项中可以得到准600 a甚至更长的周期波动;②可以判断太阳活动经典的极小期,与公认的极小期有一定的滞后性。从树轮14C含量的变化趋势中可以判断从1954~2100年的太阳活动变化逐渐变强,从2100~2350年太阳活动逐渐开始变弱;③从每个尺度周期波动的时变特征中可以得到,即使在太阳活动的极小期,太阳活动依然存在频率和强度不同的周期波动。     

中国东部沿海地区乡村发展类型及其乡村性评价

在界定农业主导、工业主导、商旅服务和均衡发展四个乡村发展类型的基础上,对中国东部沿海地区的乡村发展类型进行了划分.基于乡村对社会具有的功能构建了乡村性指数(RI)以刻划不同发展类型的乡村性强弱,并对东部沿海地区各发展类型的乡村性进行了评价.结果表明:东部沿海地区57.6%的县市一、二、三产业得到均衡发展:农业主导、工业主导和商旅服务业主导的发展地域类型分别占总面积的18.64%、11.99%和11.75%:农业主导乡村发展类型中乡村性较强(RI>0.5)的地域占到59.1%:工业主导乡村发展类型中乡村性弱(RI<0.4)和居中(0.4相似文献   

Time-domain computation of scattering from a heterogeneous layer

Adopting Born and ray approximations, time-domain synthetic seismograms for P-P and P-S scattering from a plane wave incident on a thin, laterally heterogeneous layer are presented in this paper. The time-domain P coda is a convolution between a structure function and the second-order derivative of the time function of the incident P wave. Examples of synthetic seismograms are given using a time function from a computed short-period seismogram for a point explosive source in a half-space. These show that it is impossible, with realistic values of the parameters involved, to generate significant codas when only single scattering is involved.     

Cagniard de-Hoop method for a Haskell type vertical fault

Summary. There are two ways to apply the Cagniard de-Hoop method when generating synthetic seismograms due to a source in a three-dimensional medium. One is the Hankel transform method (hereafter called 'the cylindrical wave representation method'), which utilizes the property of the modified Bessel function. The other is 'the plane wave representation method', which replaces the Bessel function by a superposition of plane waves. In extending a point source to a finite dimensional source, the latter method is extremely useful, because it enables the integrations on the fault surface to be performed analytically.
Using the latter method, expressions for displacements due to a Haskell type vertical fault in a uniform half-space are obtained. A solution is given as a sum of four quadrantal source contributions, which is similar to Madariaga's solution for a source in the whole space. Each contribution consists of a single finite range integration or a single integration plus a pole contribution, depending on the location of the observation point with respect to the source. The procedure can be extended to other fault types.     

A Systems Perspective on World-Systems Theory

Abstract

This article presents a conceptual framework that embeds ideas from world-systems theory within the larger systemic context known as the theory of dissipative structures. This article creates a theoretical perspective on global capitalism, both geographic and historical, that offers a sufficiently general and flexible model for this particular complex system in human geography. The goal is to provide a perspective that reflects the interconnectedness of individual and separate places into a larger global system that is a single functioning spatial entity. In this view, the modern world-system becomes a culmination of its past and a prologue to its future.     

Representing the visibility structure of a polyhedral terrain through a horizon map

Abstract

We present a model for describing the visibility of a polyhedral terrain from a fixed viewpoint, based on a collection of nested horizons. We briefly introduce the concepts of mathematical and digital terrain models, and some background notions for visibility problems on terrains. Then, we define horizons on a polyhedral terrain, and introduce a visibility model, that we call the horizon map. We present a construction algorithm and a data structure for encoding the horizon map, and show how it can be used for solving point visibility queries with respect to a fixed viewpoint.     

塔里木盆地南缘和田绿洲中全新世以来气候环境变化与人类活动

塔里木盆地南缘和田绿洲约特干遗址剖面多指标综合地记录到了近6.7 ka BP以来的环境变化。考虑到此地区人类活动的历史,各指标的变化记录了自6.7—4.0 ka BP期间环境变化的自然过程,揭示出6.5—6.7 ka BP期间的显著湿润期以及出现于4.0 ka BP之后的转干和3.0 ka BP前后的相对冷湿期。自2.0 ka BP开始,人类活动的影响渐趋于显著。     

Co-Phase Analysis of Atmospheric Wave Data

Summary Co-phase is a statistic designed for the detection and parameter estimation of signals by detector arrays. Ionospheric motions detected by an array of four phase-path sounders following a large earthquake are found by the co-phase technique to have a phase velocity equal to that of seismic Rayleigh waves of the same period, and to arrive from the direction of the epicentre. The calculation of co-phase for an 80-min sample of data from an 8-element array of microbarographs detects the presence of a signal from a high energy event despite a signal-to-noise ratio of less than unity. Co-phase analysis of acoustic signals generated by the Saturn-Apollo rocket launches indicates that these signals originate at ionospheric heights and propagate in a waveguide between a soundspeed maximum and a steep density gradient in the mesosphere.     

Laboratory Work in Secondary School Geography

Abstract

Determining the direction in which to face another location on the globe is a problem with significant social and religious meaning, and one with a rich and interesting history in the Western world. Yet a fully satisfying geographic solution to this problem is hindered by our intuitive perception of the world as a flat surface-where a “straight” path (1) is the shortest distance, and (2) maintains a constant angle. On a curved surface, however, only one of these two properties can be satisfied: the first, by a great circle; the second, by a rhumb line. These two solutions are analyzed, compared, and applied to the direction-facing problem.     

Effects of weak climatic variations on assemblages and life cycles of Orthoptera in North Algeria

A study on orthopterologic diversity was carried out in two stations situated at 25 km (Soumàa) and 4 km (Koléa) from the Mediterranean Sea in the Mitidja plain (North Algeria) between 1991 and 1992. Mean temperatures are higher in Soumàa than in Koléa, the dry period begins earlier, at the end of spring, in Koléa. The two stations show a diversified entomofauna, as 28 species were listed in Koléa and 24 in Soumàa. Three seasonal assemblages were defined, the summer-autumn one significantly differs between the two stations, especially for minority species. The life cycle of larvae was investigated for 6 dominant species in both stations. Four species present a precocious hatching in Koléa, but with a longer duration of larval life. The two species that accomplish their larval life earlier in Koléa than in Soumàa show the greatest lag in hatching date, suggesting an adaptation to the early onset of the dry period. The longer larval life of Ochrilidia harterti in Koléa is discussed in the light of a possible supernumerary larval stage.     

A path that buys time to decide where to go

This paper considers the problem of planning a path in a circumstance where its origin is given, but its destination is not specified and is to be selected from among a set of candidate destinations during a trip. A situation like this may be experienced by a group of people who have different preferred destinations, as well as by an individual who is simply indecisive about where to go. To resolve such an uncertainty, one may stay at the origin until he decides on a destination, or choose to proceed on some path that does not overly deviate from a shortest path, whichever destination is eventually chosen, and make a decision on the way. The latter action is sensible when the risk of traveling longer is outweighed by the benefit of buying more time for a better destination decision. The problem of finding such a time-buying path is formulated and a simple algorithm is developed for its solution. Some extensions and applications are also discussed.     

Polarization and amplitude attributes of reflected plane and spherical waves

The characteristics of a reflected spherical wave at a free surface are investigated by numerical methods; in particular, the polarization angles and amplitude coefficients of a reflected spherical wave are studied. The classical case of the reflection of a plane P wave from a free surface is revisited in order to establish our terminology, and the classical results are recast in a way which is more suited for the study undertaken. The polarization angle of a plane P wave, for a given angle of incidence, is shown to be 90° minus twice the angle of reflection of the reflected S wave. For a Poisson's ratio less than 1/3, there is a non-normal incident angle for which both amplification coefficients are 2 precisely; for this incident angle the direction of the particle motion at the free surface is also the direction of the incident wave. For a wave emanating from a spherical source, the polarization angle, for all angles of incidence, is always less than, or equal to, the polarization angle of a plane P wave. The vector amplification coefficient of a spherical wave, for all angles of incidence, is always greater than the vector amplification coefficient of a plane P wave. As expected, the results for a spherical wave approach the results for a plane P wave in the far field. Furthermore, there was a good agreement between the theoretical modelling and the numerical modelling using the dynamic finite element method (DFEM).     

World Cities in the Pacific Rim: A New Global Test of Regional Coherence

A new evaluation of the Pacific Rim concept is presented. The originality of this test for regional coherence is to be found in the basic units being analysed: cities instead of states. Based on a theoretical framework that identifies world city and world city network formation in terms of the office networks of advanced producer service firms, we use a principal components analysis to analyse a data set of 28 Pacific Rim cities and 46 global service firms. This identifies five main groupings of cities in terms of similar mixes of corporate service firms: a western Rim group; a group of ‘old Commonwealth’ cities; a market communist group of cities; Tokyo as a global city; and US cities as a specific separate group. These results confirm numerous earlier studies that were sceptical of the existence of a coherent Pacific Rim region. However, the particular approach adopted here allows us to identify the Pacific Rim generically as a particularly pernicious construct. We conclude that the Pacific Rim is a geographical chaotic conception.     

毛乌素沙地北缘泊江海子剖面粒度特征及环境意义

通过毛乌素沙地现代风成沙的粒度与泊江海子剖面沉积物粒度特征对比分析,确定了剖面中4个层位（290—210 cm、190—160 cm 、153.5—123.5 cm、50—40 cm）基本属于风成砂沉积,并且这些风成砂中间夹杂着三次湖相沉积,结合14C年代测定,我们认为此区域在4 000—5 000 a BP存在以下沉积（气候）旋回:至(4 958±84)a BP,沉积风成砂,反映该时期风沙活动强烈,气候干燥,冬季风强盛;(4 958±84)a BP前后,沉积物为灰绿色湖相层,表明这一时期存在短暂的湖面扩展,沙漠退缩;(4 958±84)—(4 793±74)a BP,沉积风成砂,反映了湖泊的退缩和沙漠的扩展;(4 793±74)—(4 536±70)a BP,湖相沉积物,反映了流域降水量的增多;(4 536±70)—(4 085±67)a BP沉积风成砂后,(4 085±67)a BP前后又出现了短暂的湖相沉积,之后又是风成砂沙沉积。     

Hyper‐planning Jakarta: The Great Garuda and planning the global spectacle

After a major flood in Jakarta in 2007, the government of Indonesia partnered with a consortium of Dutch engineers and designers to produce a solution. In 2013, this consortium proposed a plan for the Great Garuda, a megaproject that combined a deep seawall and private real estate, both in an archipelago of reclaimed islands that would be shaped like the mythical garuda eagle, Indonesia's national symbol. Despite a range of infeasibilities and opposition, the Great Garuda became the most prominent vision for the city's future. This article argues that the promotion of the Great Garuda was a process of ‘hyper‐planning’, which projected the city as a national triumph and a global spectacle. The plan served the political objective of creating the mere possibility of a ‘new Jakarta’ apart from the perceived chaos of the current capital. Further, the plan functioned as a performative object through its iconic imagery and its circulations. The process of hyper‐planning simultaneously projected a future of urban success, but also displaced the contingencies of the future to the private sector, beyond the purview of the state.