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Angular resolution of terrestrial laser scanners 总被引：5，自引：0，他引：5
Knowledge of a laser scanner's spatial resolution is necessary in order to prevent aliasing and estimate the level of detail that can be resolved from a scanned point cloud. Spatial resolution can be decoupled into range and angular components. The latter is the focus of this paper and is governed primarily by sampling interval and laser beamwidth. However, emphasis is often placed on one of these—typically sampling interval—as an indicator of resolution. Since both affect the resolution of a scanned point cloud, consideration of only one factor independent of the other can lead to a misunderstanding of a system's capabilities. This will be demonstrated to be inappropriate except under very specific conditions. A new, more appropriate resolution measure for laser scanners, the effective instantaneous field of view (EIFOV), is proposed. It is derived by modelling the shift variance of the equal angular increment sampling process, laser beamwidth-induced positional uncertainty and observed angle quantisation with ensemble average modulation transfer functions (AMTFs). Several commercially available terrestrial laser scanner systems are modelled and analysed in terms of their angular resolution capabilities using the EIFOV. 相似文献
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Sherpa Sonam Futi Shrestha Milan Eakin Hallie Boone Christopher G. 《Natural Hazards》2019,96(2):607-626
Glacial lake outburst floods (GLOFs) are among the most serious cryospheric hazards for mountain communities. Multiple studies have predicted the potential risks posed by rapidly expanding glacial lakes in the Sagarmatha (Mt. Everest) National Park and Buffer Zone of Nepal. People’s perceptions of such cryospheric hazards can influence their actions, beliefs, and responses to those hazards and associated risks. This study provides a systematic approach that combines household survey data with ethnography to analyze people’s perceptions of GLOF risks and the socioeconomic and cultural factors influencing their perceptions. A statistical logit model of household data showed a significant positive correlation between the perceptions of GLOF risks and livelihood sources, mainly tourism. Risk perceptions are also influenced by spatial proximity to glacial lakes and whether a village is in potential flood zones. The 2016 emergency remediation work implemented in the Imja Tsho (glacial lake) has served as a cognitive fix, especially in the low-lying settlements. Much of uncertainty and confusions related GLOF risks among locals can be attributed to a disconnect between how scientific information is communicated to the local communities and how government climate change policies have been limited to awareness campaigns and emergency remediation efforts. A sustainable partnership of scientists, policymakers, and local communities is urgently needed to build a science-driven, community-based initiative that focuses not just in addressing a single GLOF threat but develops on a comprehensive cryospheric risk management plan and considers opportunities and challenges of tourism in the local climate adaptation policies.
相似文献3.
Shantikumar S. Ningombam S. Kathiravan P. S. Parihar E. J. L. Larson Sharika Mohanan Dorje Angchuk Sonam Jorphel K. E. Rangarajan K. Prabhu 《Experimental Astronomy》2017,43(2):145-165
The present work discusses astronomical site survey reports on dust content, vertical distribution of atmospheric turbulence, precipitable water vapor (PWV), surface and upper-air data, and their effects on seeing over the Indian Astronomical Observatory (IAO) Hanle. Using Laser Particulate Counter, ambient dust measurements at various sizes (0.3 μm to 25 μm) were performed at various locations at the site during November 2015. Estimated volume concentration for the particle size at 0.5 μm was around 10,000 per cubic foot, which is equivalent to ten thousand class of clean room standard protocol. During the measurement, surface wind speed varied from 0-20 m s ?1, while estimated aerosol optical depth (AOD) using Sky radiometer (Prede) varied from 0.02-0.04 at 500 nm, which indicates the site is fairly clean. The two independent measurements of dust content and aerosol concentrations at the site agreed well. The turbulence or wind gust at the site was studied with wind profiles at three different heights above the ground. The strength of the wind gust varies with time and altitude. Nocturnal temperature across seasons varied with a moderate at summer (6?8 °C) and lower in winter (4?5 °C). However, the contrast between the two is significantly small due to cold and extremely dry typical climatic conditions of the site. The present study also examined the effects of surface and upper-air data along with Planetary Boundary Layer (PBL) dynamics with seeing measurement over the site. Further, a comparative study of such observed parameters was conducted with other high altitude astronomical observatories across the globe. 相似文献
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A clear and present danger: Ladakh's increasing vulnerability to flash floods and debris flows 
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下载免费PDF全文 Alan D. Ziegler Sebastian I. Cantarero Robert J. Wasson Pradeep Srivastava Sonam Spalzin Winston T. L. Chow Jamie Gillen 《水文研究》2016,30(22):4214-4223
This preliminary investigation of the recent spate of deadly flash floods and debris flows in Ladakh (India) over the last decade identifies uncontrolled development in hazardous locations as an important factor contributing to loss of life and property damage in this high mountain desert. The sediments exposed in the channel banks and on the alluvial fans of several mountain streams in the area indicate a long history of flash floods and debris flows resulting from intense storms, which appear to have increased in frequency within the last decade. The signposts of these recurrent hazards are being ignored as a growing economy, which is boosted by a well‐established tourism industry, is now driving development onto lands that are susceptible to floods and debris flow hazards. In this science briefing we argue that the increasing vulnerability in Ladakh should be addressed with sound disaster governance strategies that are proactive, rather than reactionary. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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西藏高原农业界限温度的变化特征 总被引：2，自引：0，他引：2
根据西藏1971～2000年≥0℃、10℃界限温度资料,建立了小网格推算模式,应用GIS推算出500m×500m网格点上的农业界限温度值,分析了界限温度的空间分布特征、趋势变化、年代际变化和气候异常。结果表明:界限温度持续日数及积温总的分布趋势自东南向西北减小,并随着海拔高度的升高、纬度的增大而减小。过去30年,西藏大部分站点≥0℃表现为初日提早、终日推迟、持续日数延长、积温增加的趋势。20世纪70年代,各站点≥0℃积温偏少,持续日数较短;主要农区≥10℃积温呈逐年代增加趋势,90年代热量最充足。前20年西藏各站点≥0℃的积温未出现过异常偏高年,90年代后期大部分站点发生了异常偏高年。 相似文献
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Derek D. Lichti Changjae Kim Sonam Jamtsho 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):360-368
This paper describes a new method for integrated range camera system self-calibration in which both traditional camera calibration parameters and rangefinder systematic error parameters are estimated simultaneously in a free-network bundle adjustment of observations to signalised targets. Its mathematical basis is collinearity and range observation equations augmented with correction models for systematic error sources identified in the data. The self-calibration results from datasets captured with two different range cameras, a SwissRanger SR3000 and a SwissRanger SR4000, are presented and analysed in detail. The method’s effectiveness is demonstrated in terms of systematic error removal and independent accuracy assessment. Up to a 54% reduction in the residual RMS was achieved by inclusion of the proposed error models in the self-calibration adjustment. An improvement of at least 74% in the RMS of object point co-ordinate differences, over that achieved without calibration or provided by the manufacturer’s software (in the case of the SR3000), was realised in an independent accuracy assessment. In addition, the effects of several influencing variables, including the range stochastic error model, the network geometry and the range measurements themselves, on key correlation mechanisms are analysed in detail. 相似文献
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Phenomenal progress has been witnessed in the field of Geographic Information System (GIS) in recent times. The development of webGIS is the result of the growth of the Internet and consequently World Wide Web. The webGIS architecture is continuously changing according to contemporary technologies and requirements. In this paper, webGIS and its architectures are reviewed. Firstly, GIS and invention of the Internet are discussed. Evolution of webGIS is then covered along with major milestones of its development and open source initiatives. It is followed by discussion on client server architecture and its types. Thick and thin client architectures are then described and compared. As the paradigm in the computing world shifted towards web services, service-oriented architecture (SOA) is also discussed in context of webGIS. Spatial cloud computing and cloud-based architecture for webGIS are then described. The paper also provides a comparison of different webGIS architectures so that suitable architecture can be selected by the user based upon the requirements. 相似文献
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