Earthquake-induced landslide hazard and vegetation recovery assessment using remotely sensed data and a neural network-based classifier: a case study in central Taiwan   总被引：4，自引：1，他引：3  

Wen-Tzu Lin  Wen-Chieh Chou  Chao-Yuan Lin 《Natural Hazards》2008,47(3):331-347

A catastrophic earthquake with a Richter magnitude of 7.3 occurred in the Chi-Chi area of Nantou County on 21 September 1999. Large-scale landslides were generated in the Chiufenershan area of Nantou County in central Taiwan. This study used a neural network-based classifier and the proposed NDVI-based quantitative index coupled with multitemporal SPOT images and digital elevation models (DEMs) for the assessment of long-term landscape changes and vegetation recovery conditions at the sites of these landslides. The analyzed results indicate that high accuracy of landslide mapping can be extracted using a neural network-based classifier, and the areas affected by these landslides have gradually been restored from 211.52 ha on 27 September 1999 to 113.71 ha on 11 March 2006, a reduction of 46.24%, after six and a half years of assessment. In accordance with topographic analysis at the sites of the landslides, the collapsed and deposited areas of the landslide were 100.54 and 110.98 ha, with corresponding debris volumes of 31,983,800 and 39,339,500 m³. Under natural vegetation succession, average vegetation recovery rate at the sites of the landslides reached 36.68% on 11 March 2006. The vegetation recovery conditions at the collapsed area (29.17%) are shown to be worse than at the deposited area (57.13%) due to topsoil removal and the steep slope, which can be verified based on the field survey. From 1999 to 2006, even though the landslide areas frequently suffered from the interference of typhoon strikes, the vegetation succession process at the sites of the landslides was still ongoing, which indicates that nature, itself, has the capability for strong vegetation recovery for the denudation sites. The analyzed results provide very useful information for decision-making and policy-planning in the landslide area.  相似文献   

The effect of imposing ‘fractional abundance constraints’ onto the multilayer perceptron for sub-pixel land cover classification     

《International Journal of Applied Earth Observation and Geoinformation》2016

To be physically interpretable, sub-pixel land cover fractions or abundances should fulfill two constraints, the Abundance Non-negativity Constraint (ANC) and the Abundance Sum-to-one Constraint (ASC). This paper focuses on the effect of imposing these constraints onto the MultiLayer Perceptron (MLP) for a multi-class sub-pixel land cover classification of a time series of low resolution MODIS-images covering the northern part of Belgium. Two constraining modes were compared, (i) an in-training approach that uses ‘softmax’ as the transfer function in the MLP’s output layer and (ii) a post-training approach that linearly rescales the outputs of the unconstrained MLP. Our results demonstrate that the pixel-level prediction accuracy is markedly increased by the explicit enforcement, both in-training and post-training, of the ANC and the ASC. For aggregations of pixels (municipalities), the constrained perceptrons perform at least as well as their unconstrained counterparts. Although the difference in performance between the in-training and post-training approach is small, we recommend the former for integrating the fractional abundance constraints into MLPs meant for sub-pixel land cover estimation, regardless of the targeted level of spatial aggregation.  相似文献   

Upper-ocean hydrodynamics along meridional sections in the southwest Indian sector of the Southern Ocean during austral summer 2007     

Alvarinho J. Luis  M. Sudhakar 《Polar Science》2009,3(1):13-30

This paper addresses analysis of surface meteorological and hydrographic data collected along the transects Durban–India Bay, Antarctica (Track-1) and Prydz Bay–Mauritius (Track-2) during February–March 2007 as part of the International Polar Year project (IPY#70). Strong winds (>12 m s⁻¹) resulted in enhanced turbulent heat loss north of 45°S. Whereas a highly stable marine atmospheric boundary layer (MABL) and strong winds facilitated the release of latent heat of condensation along Track-1, a highly unstable MABL and strong winds resulted in large turbulent heat loss from the sea surface along Track-2, in the 40–45°S belt. The northern and southern branches of Subantarctic Front on both tracks coalesce, while the Agulhas Retroflection Front (AF) and South Subtropical Front (SSTF) merge between 43° and 44°S on Track-2. The southern branch of the Polar Front (PF2) meanders 550 km southward towards the east. The Subtropical Surface Water, Central Water, and Mode Water are located north of 43.5°S, while the Subantarctic Surface Water, Antarctic Surface Water, Antarctic Intermediate Water, and Circumpolar Deep Water are encountered in the region of the Antarctic Circumpolar Current (ACC). Baroclinic transport relative to 1000 db reveals that the ACC is enhanced by 10 × 10⁶ m³ s⁻¹ eastward, and a four-fold increase in transport occurs south of the ACC. Nearly 50% of the ACC transport occurs in the 100–500 m slab. We discuss the effects of the feedback of AC and hydrological fronts on the MABL.  相似文献   

台风过境对黄海冷水团及其环流结构的影响     

孙凡  于非  司广成  王建丰  唐瑛 《海洋与湖沼》2021,52(5):1125-1136

台风能够对黄海的水文结构及人民群众的生产生活产生重要的影响,严重威胁了人们的生命财产安全。利用ROMS(regional ocean modeling system)模式,分析了台风"灿鸿"在过境黄海期间对黄海温度及环流结构的影响过程。结果表明,台风期间强烈的风致混合能够使温跃层的深度增大,强度减弱,同时,使得近岸的底层温度迅速升高,推动底层的温度锋面向黄海内区移动。台风过境也会对黄海冷水团环流产生重要的影响,台风过境前,混合层中的北向流会迅速加深增强,同时伴随着混合层及温跃层的下移,从而使得黄海冷水团环流的流核下移至跃层以下。当台风过境时,黄海上空的气旋式风场会加剧黄海上层的气旋式环流,导致黄海冷水团环流的流幅及流量迅速增加。当台风登陆后,黄海上层的温度及黄海冷水团环流的结构开始逐渐恢复。  相似文献   

Seasonal variation in the three-dimensional structures of coastal thermal front off western Guangdong     

Yan Zhang  Lili Zeng  Qiang Wang  Bingxu Geng  Changjian Liu  Rui Shi  Na Liu  Weiping Wang  Dongxiao Wang 《海洋学报(英文版)》2021,40(7):88-99

The seasonal structure and dynamic mechanism of oceanic surface thermal fronts(STFs) along the western Guangdong coast over the northern South China Sea shelf were analyzed using in situ observational data, remote sensing data, and numerical simulations. Both in situ and satellite observations show that the coastal thermal front exhibits substantial seasonal variability, being strongest in winter when it has the greatest extent and strongest sea surface temperature gradient. The winter coastal thermal front begins to appear in November and disappears after the following April. Although runoff water is more plentiful in summer, the front is weak in the western part of Guangdong. The frontal intensity has a significant positive correlation with the coastal wind speed,while the change of temperature gradient after September lags somewhat relative to the alongshore wind. The numerical simulation results accurately reflect the seasonal variation and annual cycle characteristics of the frontal structure in the simulated area. Based on vertical cross-section data, the different frontal lifecycles of the two sides of the Zhujiang(Pearl) River Estuary are analyzed.  相似文献   

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea     

F. Chen  G.I. Shapiro  K.A. Bennett  S.N. Ingram  D. Thompson  C. Vincent  D.J.F. Russell  C.B. Embling 《Marine pollution bulletin》2017,114(1):372-383

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~ 20 dB at a frequency of 125 Hz, and ~ 10 dB on average over 10–1000 Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.  相似文献   

The motion of magnetic fronts in spiral galaxies     

D. Moss  A. Petrov  D. Sokoloff 《地球物理与天体物理流体动力学》2013,107(1-2):129-149

Abstract

We study the nonlinear asymptotic thin disc approximation to the mean field dynamo equations, as applicable to spiral galaxies. The circumstances in which sharp magnetic field structures (fronts) can propagate radially are investigated, and an expression for the speed of propagation derived. We find that the speed of an interior front is proportional to η//R _? (where η is the diffusivity and R_t the galactic radius), whereas an exterior front moves with speed of order , where γ is the local growth rate of the dynamo. Numerical simulations are presented, that agree well with our asymptotic results. Further, we perform numerical experiments using the 'no-z' approximation for thin disc dynamos, and show that the propagation of magnetic fronts in this approximation can also be understood in terms of our asymptotic results.  相似文献   

双叶模型在冬小麦田冠层CO2通量多层模拟中的应用     

申双和  张雪松  欧阳竹 《气象学报》2011,69(5):819-829

综合考虑农田生态系统中水、热、CO2输送所涉及的大气、水文、生物等生物物理过程,以Farquhar等提出的叶片尺度光合作用生物化学过程机理模型为理论基础,对其进行空间尺度扩展,并改进冠层分层方法,建立了均匀农田与大气之间物质输送和能量交换的多层模式,在模式中运用双叶模型,同时考虑叶片氮素水平垂直差异,对2008年4—5月华北平原冬小麦生长旺季农田生态系统中冠层CO2通量进行了模拟研究,并利用涡度相关观测的通量数据对模型的有效性加以验证,结果表明:在冠层多层空间,小麦拔节至孕穗期和开花至乳熟期叶片氮含量随冠层高度的衰减系数分别为0.793(R2=0.698)和1.374(R2=0.728),冠层内叶片氮含量的空间分布可以用以相对累积叶面积指数为自变量的函数来描述;模型分别计算各层阴、阳叶的光截取、气孔传导、光合作用等,最终计算冠层上方CO2通量,冬小麦农田净生态系统生产力模拟值与实测值相关显著(R2=0.78),模拟的CO2通量日变化特征晴天昼间比阴雨天和夜间的效果好;在考虑丛聚影响的叶片非随机分布的密集农田中,阴叶对总初始生产力的贡献率在35.7%左右,对生产力贡献很重要。分层统计显示,作物最终产量的形成主要...  相似文献   

Suspended particulate matter and dynamics of the Mfolozi estuary,Kwazulu-Natal: Implications for environmental management     

P. Lindsay  T. R. Mason  S. Pillay  C. I. Wright 《Environmental Geology》1996,28(1):40-51

 The Mfolozi Estuary on the KwaZulu-Natal coast of South Africa is the most turbid estuary in Natal due to poor catchment management, leading to large quantities of suspended particulate matter (SPM) entering the estuary from the Mfolozi River. This paper quantities some of the solute and sediment dynamics in the Mfolozi Estuary where the main documented environmental concern is the periodic input of SPM from the Mfolozi Estuary to the St. Lucia system, causing reduction of light penetration and endangering biological productivity in this important nature reserve. Synoptic water level results have allowed reach mean bed shear stresses and velocities to be calculated for an observed neap tidal cycle. Results indicate that ebb velocities dominate the sediment transport processes in the estuary when fluvial input in the Mfolozi River is of the order of 15–20 m³ s^–1. Observed and predicted flood tide velocities are too low (<0.35 m s^–1) to suspend and transport significant amounts of SPM. Observed results indicate that although the SPM load entering the estuary is dominantly from the Mfolozi River, the Msunduzi River flow plays a major role in the composition of the estuary's salinity and velocity fields. It is calculated that the Mfolozi Estuary would fill with sediment in 1.3 years if it was cut off from the sea. The major fluvial flood events help maintain the estuary by periodically pushing sediment seawards (spit progrades seawards 5 m yr^–1) and scouring and maintaining the main flow channel in the estuary. During low fluvial flow conditions, tidal flow velocities will become the dominant control on sediment transport in the estuary. Interchange of SPM between the St. Lucia and Mfolozi estuaries under present conditions is complicated by the strong transverse velocity shear between the two systems at their combined mouth. This is creating a salinity-maintained axial convergence front that suppresses mixing of solutes and SPM between the systems for up to 10 h of the tidal cycle during observed conditions. Received: 22 May 1995 · Accepted: 31 July 1995  相似文献   

A numerical method for the two layer shallow water equations with dry states     

《Ocean Modelling》2013

A numerical method is proposed for solving the two layer shallow water equations with variable bathymetry in one dimension based on high-resolution f-wave-propagation finite volume methods. The method splits the jump in the fluxes and source terms into waves propagating away from each grid cell interface. It addresses the required determination of the system’s eigenstructure and a scheme for evaluating the flux and source terms. It also handles dry states in the system where the bottom layer depth becomes zero, utilizing existing methods for the single layer solution and handling single layer dry states that can exist independently. Sample results are shown illustrating the method and its handling of dry states including an idealized ocean setting.  相似文献