Effect of data density,scan angle,and flying height on the accuracy of building extraction using LiDAR data     

Bharat Lohani  Rajneesh Singh 《国际地球制图》2013,28(2):81-94

A Hough transform based approach for extraction of buildings using LiDAR data is presented. It is argued that LiDAR data should be smoothed and sparsed prior to Hough transform for better result. Algorithms to realize this are presented. Further, an algorithm which fits a vector model to extracted buildings is outlined. Simulated LiDAR data have been used to investigate the effect of three parameters (data density, flying height, and scan angle) on the quality of buildings extracted. A set of accuracy indices is proposed for this purpose. It is shown that the data density is the most significant parameter affecting the accuracy of building identification.  相似文献   

A class of inhomogeneous shear models for seismic analysis of landfills     

Venkata Ramana Gunturi  Ahmed-W.M. Elgamal 《Soil Dynamics and Earthquake Engineering》1998,17(3):197-209

An analytical/numerical procedure is developed to calculate the shear elasto-plastic earthquake response of hill-shaped landfills. Landfill response is evaluated on the basis of newly developed one-dimensional inhomogeneous shear beam models. In these models, the nonhomogeneity of landfill materials is taken into account by assuming a specific variation of stiffness properties along the depth. Closed-form analytical expressions are derived for natural frequencies, modal displacements, modal participation factors, absolute accelerations and maximum shear strains. Parametric results are presented in graphical and tabular form and conclusions are drawn. Within a numerical implementation framework of the above formulation, the landfill materials may be modeled by an elasto-plastic hysteretic model following the principles of flow or incremental plasticity. The entire numerical procedure may be executed on a personal computer and consequently qualifies as a versatile tool for conducting preliminary design calculations or parametric-type investigations. Using this newly developed procedure, the seismic response of the Fresh Kills landfill in New York City is investigated.  相似文献   

Surface Boundary-Layer Characteristics Over a Tropical Inland Station: Seasonal Features     

Muvva Venkata Ramana  Praveena Krishnan  P. K. Kunhikrishnan 《Boundary-Layer Meteorology》2004,111(1):153-157

Some characteristic features of the atmospheric surfacelayer over an inland tropical station, Lucknow (27°N, 81°E)in India, are investigated for different seasons using micrometeorological data collected at the 10-m levelof an instrumented tower. Seasonal monsoonal variations in wind circulation (north-easterliesand south-westerlies) dominate the flow over this part of the region. This study utilizesthe wind, temperature and humidity data obtained for a period of one year from February 1996 to January 1997. The diurnal variation of mean parameterssuch as temperature, relative humidity, and wind speed are studied for different seasonsnamely pre-, south-west, post- and north-east monsoon periods. Turbulent statistics are computedusing the eddy correlation technique, and are studied under the framework of Monin–Obukhov similarity theory with results compared with otherexperimental studies reported in the literature. It is found that the turbulence statistics arenearly independent of season and the near-neutral values of the normalized standard deviations ofthe three wind components, temperature and specific humidityare found to be 1.00 ± 0.04 (vertical), 2.63 ± 0.36(longitudinal), 2.19 ± 0.06 (lateral), 6.56 ± 0.33and 6.45 ± 0.33 respectively.  相似文献   

On the recurvature of tropical cyclones and the storm surge problem in Bangladesh     

Tad S. Murty  Venkata R. Neralla 《Natural Hazards》1992,6(3):275-279

The disproportionality of the large frequency of occurrence of severe storm surges on the coast of Bangladesh is highlighted. The reasons for the recurvature of these storms towards the Bangladesh coast and the associated severe surges are discussed in this paper.Atmospheric Environment Service, Ice Center, Environment Canada, 373 Sussex Drive, Ottawa, Ontario, Canada K1A 0H3.  相似文献   

Influence of Co‐Factor on Enhancement of Bioplastic Production through Wastewater Treatment          下载免费PDF全文

Motakatla Venkateswar Reddy  Dhulipala Naga Sri Krishna Chitanya  Gauravarapu Navlur Nikhil  S. Venkata Mohan  Ponnapalli Nageswara Sarma 《洁净——土壤、空气、水》2014,42(6):809-814

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Coupled horizontal–vertical stability of bearings under dynamic loading          下载免费PDF全文

Venkata S. M. Vemuru  Satish Nagarajaiah  Gilberto Mosqueda 《地震工程与结构动力学》2016,45(6):913-934

In this study, the coupled horizontal–vertical behavior of elastomeric bearings subjected to dynamic loading is studied in detail. Under extreme dynamic loading, elastomeric bearings exhibit unstable behavior and an instantaneous loss of horizontal stiffness that is recoverable. Building on an earlier study where the authors developed an analytical model for the horizontal behavior of bearings under dynamic loads, in this study, a new analytical model for the coupled horizontal–vertical behavior of the bearings is developed. The coupled behavior of the bearing is first studied for quasi‐static loading, and later, the behavior of the bearings under dynamic loading is studied. A clear distinction is made between different types of deformation the bearing undergoes in the vertical direction. Based on experimental results, it is observed that the behavior of the bearings under dynamic loading differs markedly from that observed under static loading. A new analytical model is proposed that can account for the coupled horizontal–vertical behavior of the bearings under dynamic loading. The proposed analytical model for predicting the post‐stability vertical behavior of the bearings is verified using experimental results. The model proposed is found to successfully predict the coupled horizontal–vertical behavior of elastomeric bearings. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Kaolinite – alkali interaction and effects on basic properties     

Puvvadi?Venkata?SivapullaiahEmail author  Manju 《Geotechnical and Geological Engineering》2005,23(5):601-614

The influence of type and amount of clays present in soils on their properties is well understood. The clays exert their influence through large specific surface area and charges on them. Their effect is mostly exhibited through inter particle bonding and subsequent particle associations. The mineralogical influence of soils in water is well documented. However, the change in soil water system because of presence some of the contaminants can greatly influence the soil behaviour. Some of the changes are due to formation of new compounds due to interactions between the soil and pollutant. The paper reports the effect of interaction of kaolinite mineral with alkali on the index properties of soils from which the geotechnical behaviour can be understood. Detailed X-ray diffraction studies have shown that sodium aluminum silicate hydroxide hydrate (NASH) is formed by clay alkali reactions. The type and amount of formation of the compound is influenced by the concentration of alkali solution. While the compound formed is in smaller quantities with 1 N NaOH solution, significantly high quantity is formed with 4 N NaOH solution. Presence of alumina is shown to play a significant role. It was observed that the formation of sodium aluminum silicate hydroxide hydrate is reduced in the presence of alumina. Specific gravity of contaminated clay soil was reduced which confirms the formation of new compounds. Water adsorption and specific surface area of soil are also influenced due to soil alkali interaction. The changes in the free swell and index properties of soil in the presence of alkali have been explained by the changes in soil fabric and the formation of new compound.  相似文献   

Economic Contribution of Forestry Sector to National Economy in Nepal     

Bharat Prashad BHATT  Sagar GODAR CHHETRI  Thakur SILWAL  Megharaj POUDEL 《资源与生态学报(英文版)》2021,12(5):620-627

Forests are major sources of energy, timber and non-timber forest products, medicinal and aromatic plants, hydrological functions, biodiversity conservation, and also fundamental sources of revenue collection to the nation. Studies indicate that forests could significantly enhance economic growth and create employment opportunities for local communities under intensive management. This paper aims to predict the contribution of the forest sector to the national economy. The economic facets of forestry considered in this paper are revenue generated from timber, non-timber forest products (NTFPs) and medicinal and aromatic plants (MAPs), and protected areas. The ARIMA model was used to forecast the economic contribution of the forestry sector. The study found that the total revenue generated from the selling of timber and fuelwood (USD 50.19 million) was higher than the total revenue collected from protected areas (USD 37.58 million) and NTFPs/MAPs (USD 6.9 million) in the past 15 years. The model projected that the mean revenue for the timber and fuelwood sale will USD 3.5 million for the next ten years. Similarly, the mean revenue will be generated about USD 0.5 million and USD 6.2 million from NTFPs/MAPs and protected areas, respectively, for the next ten years. The study limits to take account the in-kind use of forest products such as timber, fodder, fuelwood, etc., as used by community people within a forest users’ groups. Thus, practicing sustainable forest management, enabling policy documents, establishing forest-based industries, establishing forestry nurseries, conducting agroforestry practices, and tenure security could enhance the forestry sector's economic aspects.  相似文献   

Chasing Chinese Caterpillar Fungus (Ophiocordyceps sinensis) Harvesters in the Himalayas: Harvesting Practice and Its Conservation Implications in Western Nepal     

Uttam Babu Shrestha  Sujata Shrestha  Shivaraj Ghimire  Kamal Nepali  Bharat Babu Shrestha 《社会与自然资源》2014,27(12):1242-1256

The Chinese caterpillar fungus is famous for its high market value, unusual life history, and significant medicinal uses. It is harvested by very poor communities and sold for an extraordinarily high price. Most of the studies on this species are focused on therapeutic uses, chemical analyses, ecology, and trade. However, harvesting techniques and intensity of the harvests remain undocumented. We document harvesting techniques, trends of harvest, and perceptions of the Chinese caterpillar fungus harvesters in Dolpa, Nepal, based on surveys, focus-group discussions, and direct observations. Along with increasing market value, intensity of the harvest has been increasing. The Chinese caterpillar fungus harvest has now become the second most important livelihood strategy for the local communities, after agriculture. Reported per-capita harvest based on the first day of collection has declined over the last 4 years, apparently because of the decline in the stock and the increasing number of harvesters.  相似文献   

An index for tropical temperate troughs over southern Africa     

Satyaban B. Ratna  Swadhin Behera  J. Venkata Ratnam  Keiko Takahashi  Toshio Yamagata 《Climate Dynamics》2013,41(2):421-441

Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December–January–February seasons from 1980–1981 to 2009–2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event.  相似文献