The Use of LiDAR in Digital Surface Modelling: Issues and Errors     

Charlotte L Leigh  David B Kidner  Malcolm C Thomas 《Transactions in GIS》2009,13(4):345-361

Modelling and extracting 3D geographical data presents numerous challenges that require continual research to attempt to evolve an efficient, reliable and accurate solution. LiDAR data capture and analysis has become a preferred acquisition choice for elevation data because the resulting quality and level of detail far exceeds traditional methods for large survey areas. As with any data collection system, LiDAR is prone to errors. Analysing these errors, ascertaining causes and producing error correction strategies is vital if accurate and confident results are to be obtained. Eight years of LiDAR datasets (from 1998 to 2005) have been closely analysed for a large coastal area of South Wales. This article provides a detailed and accurate summary of the identified LiDAR data issues and subsequent errors which affect the accuracy of end products such as Digital Surface Models (DSMs).  相似文献   

Shell growth and oxygen isotopes in the topshell Osilinus turbinatus: resolving past inshore sea surface temperatures     

Marcello A. Mannino  Kenneth D. Thomas  Melanie J. Leng  Hilary J. Sloane 《Geo-Marine Letters》2008,28(5-6):309-325

Shells of the rocky shore intertidal gastropod Osilinus turbinatus (von Born), often abundant in archaeological deposits in the Mediterranean region, are a potential source of data on palaeotemperature, palaeoseasonality and archaeological seasonality. To evaluate this species as a climate archive, investigations of annual patterns of shell growth and of monthly variations in oxygen isotopes in shell carbonates were made on different populations in NW Sicily. Mark-recapture experiments at San Vito lo Capo and Mazzaforno show that O. turbinatus grows almost continuously throughout the year but at different rates in different seasons. Around 75% of the yearly shell growth occurs in the autumn and winter. On average, larger/older shells produce narrower annual growth increments than smaller/younger ones. Conspicuous growth lines in larger/older shells show that growth stops during the hottest part of the summer. Oxygen isotope analyses on monthly collected shells of O. turbinatus from three shores (Cala Grande, Monte Cofano and Mazzaforno) show that the isotope values record temperature variations through the year. In all the datasets, surface seawater temperatures (SSTs) calculated from δ¹⁸O_SHELL mostly underestimate measured SSTs, offsets being generally greater in summer. Minimum annual offsets range from 0.0°C to 0.7°C and maximum annual offsets from 3.1°C to 8.7°C. δ¹⁸O_SHELL values fail to record temperatures higher than 25°C. Careful selection of shells to be analysed can reduce offsets between δ¹⁸O_SHELL temperature estimates and measured SSTs for many parts of the year, except the hottest. Allowing for this, shells of O. turbinatus offer good potential as climate archives and for archaeological studies of seasonal patterns of human foraging for shellfish.  相似文献   

Unraveling subtle details of e<Emphasis Type="Italic">x</Emphasis>pendable <Emphasis Type="Italic">b</Emphasis>ottom <Emphasis Type="Italic">p</Emphasis>enetrometer (XBP) deceleration profiles   总被引：2，自引：2，他引：0  

Nina Stark  Thomas F. Wever 《Geo-Marine Letters》2009,29(1):39-45

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Protecting small cetaceans from coastal development: Impact assessment and mitigation experience in Hong Kong     

Thomas A. Jefferson  Samuel K. Hung  Bernd Würsig 《Marine Policy》2009

Since the early 1990s, there has been an active program in Hong Kong to manage and protect local populations of small cetaceans from the effects of massive development in the area. This paper reviews the progress that has been made. Only two species regularly occur there: the Indo-Pacific humpback dolphin and the finless porpoise. Because most development has occurred in the western waters of Hong Kong, where generally only the humpback dolphin occurs, most of the work has been conducted on that species. Development of large infrastructure projects (such as airports, bridges, expressways, power plants, fuel facilities, and container ports) in Hong Kong often results in land reclamation, dredging and dumping of spoils, pipe and cable laying, percussive and bored piling work, underwater blasting, large increases in vessel traffic, and other impacts. Several mitigation measures have been used with varying levels of success, including bubble curtains/jackets, exclusion zones, ramping up of piling hammers, acoustic decoupling of noisy equipment, vessel speed limits, no-dumping policies, and silt curtains. Baseline, construction-phase, and operational-phase cetacean monitoring is often conducted to evaluate the success of conservation measures put into place. The Environmental Impact Assessment process in Hong Kong has involved cetaceans to a degree perhaps higher than anywhere else in the world, and much can be learned from studying the successes and failures of this situation.  相似文献   

Loss of energy dissipation capacity from the deadzone in linear and nonlinear viscous damping devices   总被引：1，自引：1，他引：0  

Mai Tong Thomas Liebner 《地震工程与工程振动(英文版)》2007,6(1):11-20

In a viscous damping device under cyclic loading, after the piston reaches a peak stroke, the reserve movement that follows may sometimes experience a short period of delayed or significantly reduced device force output. A similar delay or reduced device force output may also occur at the damper’s initial stroke as it moves away from its neutral position. This phenomenon is referred to as the effect of “deadzone”. The deadzone can cause a loss of energy dissipation capacity and less efficient vibration control. It is prominent in small amplitude vibrations. Although there are many potential causes of deadzone such as environmental factors, construction, material aging, and manufacture quality, in this paper, its general effect in linear and nonlinear viscous damping devices is analyzed. Based on classical dynamics and damping theory, a simple model is developed to capture the effect of deadzone in terms of the loss of energy dissipation capacity. The model provides several methods to estimate the loss of energy dissipation within the deadzone in linear and sublinear viscous fluid dampers. An empirical equation of loss of energy dissipation capacity versus deadzone size is formulated, and the equivalent reduction of effective damping in SDOF systems has been obtained. A laboratory experimental evaluation is carried out to verify the effect of deadzone and its numerical approximation. Based on the analysis, a modification is suggested to the corresponding formulas in FEMA 356 for calculation of equivalent damping if a deadzone is to be considered.  相似文献   

高光谱遥感在农作物长势监测中的应用   总被引：3，自引：0，他引：3  

郑有飞 《气象与环境科学》2007,30(1):10-16

该研究是加拿大Saskatchewan Scott农作物轮作系统(ACS)研究的一部分.研究始于1994年,历时18 a,评价9个可耕种农作物产量系统的可靠性.由3种处理水平(organic,reduced,high)和3种作物多样性水平(low,diversified annual grains,diversified annual perennials)结合而产生的9个农作物产量系统,被用于监测和评价加拿大牧场不同处理和不同作物种植轮作下可耕种农作物的产量.在2003年生长季共收集了3次叶面积指数和光谱反射率的数据:生长季前期(6月)、生长季旺盛期(7月)、生长季后期(8月).叶面积指数是由LAI-2000植物冠层分析仪监测的,光谱测量是由覆盖了350～2500 nm波长范围共2215个波段的ADS便携式高光谱仪完成的.结果显示,光学测量可以用于监测农作物生长状况的差异.从生长季的早期到中期,光谱和叶面积指数在不同处理下有显著差异.7月中期是用遥感资料监测农作物长势的最佳季节;红光波段与近红外波段反射率的比值和基于这两个波段构造的归一化植被指数,是检测农作物长势的最佳植被指数.  相似文献   

A wave model for the Great Barrier Reef   总被引：1，自引：0，他引：1  

Thomas A. Hardy  Luciano B. Mason  Jason D. McConochie 《Ocean Engineering》2001,28(1):1869

A new wind wave generation model, WAMGBR, is presented that has been adapted from WAM especially for use in the complex geometry of the Great Barrier Reef. A technique (reef parameterization) has been presented that incorporates sub-grid scale dissipation caused by coral reefs. Three other improvements to WAM have been proposed. An explicit/implicit finite difference scheme has been implemented that allows for more efficient modelling (longer time steps) while maintaining diffusive characteristics that are at least as good as those of WAM. An offset in discrete angles creates more uniform diffusive characteristics. And, a transformed spherical coordinate system allows for more efficient grid sizes and smaller grid dependent refraction. Comparisons between modelling techniques and between model and measured data show that WAMGBR produces very good results in the difficult challenge of modelling both non-cyclonic and tropical cyclone waves in the geographically complex environment of the Great Barrier Reef.  相似文献   

Circulation on the north central Chukchi Sea shelf   总被引：8，自引：0，他引：8  

Thomas Weingartner  Knut Aagaard  Rebecca Woodgate  Seth Danielson  Yasunori Sasaki  Donald Cavalieri 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3150

Mooring and shipboard data collected between 1992 and 1995 delineate the circulation over the north central Chukchi shelf. Previous studies indicated that Pacific waters crossed the Chukchi shelf through Herald Valley (in the west) and Barrow Canyon (in the east). We find a third branch (through the Central Channel) onto the outer shelf. The Central Channel transport varies seasonally in phase with Bering Strait transport, and is 0.2 Sv on average, although some of this might include water entrained from the outflow through Herald Valley. A portion of the Central Channel outflow moves eastward and converges with the Alaskan Coastal Current at the head of Barrow Canyon. The remainder appears to continue northeastward over the central outer shelf toward the shelfbreak, joined by outflow from Herald Valley. The mean flow opposes the prevailing winds and is primarily forced by the sea-level slope between the Pacific and Arctic oceans. Current variations are mainly wind forced, but baroclinic forcing, associated with upstream dense-water formation in coastal polynyas might occasionally be important.Winter water-mass modification depends crucially on the fall and winter winds, which control seasonal ice development. An extensive fall ice cover delays cooling, limits new ice formation, and results in little salinization. In such years, Bering shelf waters cross the Chukchi shelf with little modification. In contrast, extensive open water in fall leads to early and rapid cooling, and if accompanied by vigorous ice production within coastal polynyas, results in the production of high-salinity (>33) shelf waters. Such interannual variability likely affects slope processes and the transport of Pacific waters into the Arctic Ocean interior.  相似文献   

New British records of Carboniferous lycopod cones     

B. A. Thomas 《Geological Journal》1978,13(1):11-14

Five species of Carboniferous lycopod cones have been identified from new British localities. Their geographical distributions have been widened and most have had their stratigraphical ranges extended. Comparisons are also made with the ranges of those dispersed spores which appear to be identical to the spores found in the cones.  相似文献   

How can we model subsurface stormflow at the catchment scale if we cannot measure it?     

Peter Chifflard  Theresa Blume  Katja Maerker  Luisa Hopp  Ilja van Meerveld  Thomas Graef  Oliver Gronz  Andreas Hartmann  Bernhard Kohl  Edoardo Martini  Christian Reinhardt‐Imjela  Martin Reiss  Michael Rinderer  Stefan Achleitner 《水文研究》2019,33(9):1378-1385

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