建筑物立面分类与DIM点云滤波     

崔颖  黄鹤  刘祥磊  罗德安 《测绘通报》2021,(3):55-59

针对目前基于近景摄影测量方法构建建筑物立面模型过程中因密集影像匹配（DIM）点云噪声所引起的建筑物立面TIN网格模型畸变问题,本文借鉴机器学习中样本学习的思想,对建筑物立面进行了分类并对DIM点云提出了相应的滤波方法,以达到去除DIM点云噪声和改善其TIN网格模型畸变的目的。其中,针对平面结构立面,采取先对点云样本进行学习计算构建数学立面模型所需参数,再对该立面模型设定阈值并对其点云进行滤波处理的方法;针对曲面结构立面,则结合DIM点云特性先将点云样本分类标记归为立面点与非立面点,再进行样本特征值学习,使用Logistic回归算法迭代计算求解最佳回归系数,从而构建滤波分类器的方法对立面点云进行滤波处理。试验结果表明,本文滤波处理方法能将立面DIM点云噪声有效识别并去除,而且使用该方法处理后所得点云构建的建筑物立面TIN网格模型精细化程度得到有效提高,模型质量得到明显改善。  相似文献   

Updating Markov chain models using the ensemble Kalman filter   总被引：1，自引：0，他引：1  

Dean S. Oliver  Yan Chen  Geir Nævdal 《Computational Geosciences》2011,15(2):325-344

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The California Current System in relation to the Northeast Pacific Ocean circulation     

Guillermo Auad  Dean Roemmich  John Gilson 《Progress in Oceanography》2011,91(4):576-592

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Travel times for snowmelt-dominated headwater catchments: Influences of wetlands and forest harvesting,and linkages to stream water quality     

Jason A. Leach  James M. Buttle  Kara L. Webster  Paul W. Hazlett  Dean S. Jeffries 《水文研究》2020,34(10):2154-2175

The time it takes water to travel through a catchment, from when it enters as rain and snow to when it leaves as streamflow, may influence stream water quality and catchment sensitivity to environmental change. Most studies that estimate travel times do so for only a few, often rain-dominated, catchments in a region and use relatively short data records (<10 years). A better understanding of how catchment travel times vary across a landscape may help diagnose inter-catchment differences in water quality and response to environmental change. We used comprehensive and long-term observations from the Turkey Lakes Watershed Study in central Ontario to estimate water travel times for 12 snowmelt-dominated headwater catchments, three of which were impacted by forest harvesting. Chloride, a commonly used water tracer, was measured in streams, rain, snowfall and as dry atmospheric deposition over a 31 year period. These data were used with a lumped convolution integral approach to estimate mean water travel times. We explored relationships between travel times and catchment characteristics such as catchment area, slope angle, flowpath length, runoff ratio and wetland coverage, as well as the impact of harvesting. Travel time estimates were then used to compare differences in stream water quality between catchments. Our results show that mean travel times can be variable for small geographic areas and are related to catchment characteristics, in particular flowpath length and wetland cover. In addition, forest harvesting appeared to decrease mean travel times. Estimated mean travel times had complex relationships with water quality patterns. Results suggest that biogeochemical processes, particularly those present in wetlands, may have a greater influence on water quality than catchment travel times.  相似文献   

Glacial flood pulse effects on benthic fauna in equatorial high‐Andean streams          下载免费PDF全文

Sophie Cauvy‐Fraunié  Patricio Andino  Rodrigo Espinosa  Roger Calvez  Fabien Anthelme  Dean Jacobsen  Olivier Dangles 《水文研究》2014,28(6):3008-3017

Equatorial glacier‐fed streams present unique hydraulic patterns when compared to glacier‐fed observed in temperate regions as the main variability in discharge occurs on a daily basis. To assess how benthic fauna respond to these specific hydraulic conditions, we investigated the relationships between flow regime, hydraulic conditions (boundary Reynolds number, Re*), and macroinvertebrate communities (taxon richness and abundance) in a tropical glacier‐fed stream located in the high Ecuadorian Andes (> 4000 m). Both physical and biotic variables were measured under four discharge conditions (base‐flow and glacial flood pulses of various intensities), at 30 random points, in two sites whose hydraulic conditions were representative to those found in other streams of the study catchment. While daily glacial flood pulses significantly increased hydraulic stress in the benthic habitats (appearance of Re* > 2000), low stress areas still persisted even during extreme flood events (Re* < 500). In contrast to previous research in temperate glacier‐fed streams, taxon richness and abundance were not significantly affected by changes in hydraulic conditions induced by daily glacial flood pulses. However, we found that a few rare taxa, in particular rare ones, preferentially occurred in highly stressed hydraulic habitats. Monte‐Carlo simulations of benthic communities under glacial flood reduction scenarios predicted that taxon richness would be significantly reduced by the loss of high hydraulic stress habitats following glacier shrinking. This pioneer study on the relationship between hydraulic conditions and benthic diversity in an equatorial glacial stream evidenced unknown effects of climate change on singular yet endangered aquatic systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Characterizing and classifying urban watersheds with compositional and structural attributes     

Joseph M. Delesantro  Jonathan M. Duncan  Diego Riveros-Iregui  Joanna R. Blaszczak  Emily S. Bernhardt  Dean L. Urban  Lawrence E. Band 《水文研究》2021,35(9):e14339

Current land-use classifications used to assess urbanization effects on stream water quality date back to the 1980s when limited information was available to characterize watershed attributes that mediate non-point source pollution. With high resolution remote sensing and widely used GIS tools, there has been a vast increase in the availability and precision of geospatial data of built environments. In this study, we leverage geospatial data to expand the characterization of developed landscapes and create a typology that allows us to better understand the impact of complex developed landscapes across the rural to urban gradient. We assess the ability of the developed landscape typology to reveal patterns in stream water chemistry previously undetected by traditional land-cover based classification. We examine the distribution of land-cover, infrastructure, topography and geology across 3876 National Hydrography Dataset Plus catchments in the Piedmont region of North Carolina, USA. From this dataset, we generate metrics to evaluate the abundance, density and position of landscape features relative to streams, catchment outlets and topographic wetness metrics. While impervious surfaces are a key distinguishing feature of the urban landscape, sanitary infrastructure, population density and geology are better predictors of baseflow stream water chemistry. Unsupervised clustering was used to generate a distinct developed landscape typology based on the expanded, high-resolution landscape feature information. Using stream chemistry data from 37 developed headwater catchments, we compared the baseflow water chemistry grouped by traditional land-cover based classes of urbanization (rural, low, medium and high density) to our composition and structure-based classification (a nine-class typology). The typology based on 22 metrics of developed landscape composition and structure explained over 50% of the variation in NO₃⁻-N, TDN, DOC, Cl⁻, and Br⁻ concentration, while the ISC-based classification only significantly explained 23% of the variation in TDN. These results demonstrate the importance of infrastructure, population and geology in defining developed landscapes and improving discrete classes for water management.  相似文献   

Water level observations from unmanned aerial vehicles for improving estimates of surface water–groundwater interaction          下载免费PDF全文

Filippo Bandini  Michael Butts  Torsten Vammen Jacobsen  Peter Bauer‐Gottwein 《水文研究》2017,31(24):4371-4383

Integrated hydrological models are usually calibrated against observations of river discharge and piezometric head in groundwater aquifers. Calibration of such models against spatially distributed observations of river water level can potentially improve their reliability and predictive skill. However, traditional river gauging stations are normally spaced too far apart to capture spatial patterns in the water surface, whereas spaceborne observations have limited spatial and temporal resolution. Unmanned aerial vehicles can retrieve river water level measurements, providing (a) high spatial resolution; (b) spatially continuous profiles along or across the water body, and (c) flexible timing of sampling. A semisynthetic study was conducted to analyse the value of the new unmanned aerial vehicle‐borne datatype for improving hydrological models, in particular estimates of groundwater–surface water (GW–SW) interaction. Mølleåen River (Denmark) and its catchment were simulated using an integrated hydrological model (MIKE 11–MIKE SHE). Calibration against distributed surface water levels using the Differential Evolution Adaptive Metropolis algorithm demonstrated a significant improvement in estimating spatial patterns and time series of GW–SW interaction. After water level calibration, the sharpness of the estimates of GW–SW time series improves by ~50% and root mean square error decreases by ~75% compared with those of a model calibrated against discharge only.  相似文献   

Time-Series Analysis of Supergranule Characteristics at Solar Minimum     

Peter E. Williams  W. Dean Pesnell 《Solar physics》2014,289(4):1101-1113

Sixty days of Doppler images from the Solar and Heliospheric Observatory (SOHO) / Michelson Doppler Imager (MDI) investigation during the 1996 and 2008 solar minima have been analyzed to show that certain supergranule characteristics (size, size range, and horizontal velocity) exhibit fluctuations of three?to?five days. Cross-correlating parameters showed a good, positive correlation between supergranulation size and size range, and a moderate, negative correlation between size range and velocity. The size and velocity do exhibit a moderate, negative correlation, but with a small time lag (less than 12 hours). Supergranule sizes during five days of co-temporal data from MDI and the Solar Dynamics Observatory (SDO) / Helioseismic Magnetic Imager (HMI) exhibit similar fluctuations with a high level of correlation between them. This verifies the solar origin of the fluctuations, which cannot be caused by instrumental artifacts according to these observations. Similar fluctuations are also observed in data simulations that model the evolution of the MDI Doppler pattern over a 60-day period. Correlations between the supergranule size and size range time-series derived from the simulated data are similar to those seen in MDI data. A simple toy-model using cumulative, uncorrelated exponential growth and decay patterns at random emergence times produces a time-series similar to the data simulations. The qualitative similarities between the simulated and the observed time-series suggest that the fluctuations arise from stochastic processes occurring within the solar convection zone. This behavior, propagating to surface manifestations of supergranulation, may assist our understanding of magnetic-field-line advection, evolution, and interaction.  相似文献   

Effects of variable wind shear on the mesoscale circulation forced by slab‐symmetric diabatic heating     

Gerhard W. Reuter  Ole Jacobsen 《大气与海洋》2013,51(4):451-469

Abstract

We examine the response of stably stratified airflow to a slab‐symmetric diabatic forcing associated with condensation in long‐lasting precipitation bands. The steady‐state linearized Boussinesq equations are used to model the diagnostic relationship between the vertical motion field, the heating source and the ambient flow. The basic‐state flow is assumed to be horizontally uniform and non‐rotating, but the static stability and wind vary in the vertical. Linear theory shows that the speed of the along‐band wind component is unimportant for slab‐symmetric heating since it cannot contribute towards the advection of buoyancy or vertical motion.

For typical atmospheric stratification and a moving heating source associated with a cloud band, the Taylor‐Goldstein equation is solved numerically. The numerical results show that the cross‐band wind shear tilts the updraft core and broadens it. While the magnitude of the shear is increased, the circulation becomes stronger. The details of the wind profile are also important in determining the intensity and structure of the circulation. When the wind profile indicates a convex bulge (i.e. the low‐level shear is weaker than the upper‐level shear), the circulation becomes slightly weaker in comparison with the linear wind profile. Conversely, the circulation becomes stronger when the wind profile has a concave shape. Increasing the concave bulge tends to enhance the circulation but not in a monotonic fashion. This non‐monotonic relation between the vertical motion and the parabolic wind profile is interpreted in terms of kinetic energy changes of parcels that interchange their altitudes.  相似文献   

Spring and summer phytoplankton communities in the Chukchi and Eastern Beaufort Seas   总被引：2，自引：0，他引：2  

Victoria Hill  Glenn Cota  Dean Stockwell 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3369

Phytoplankton pigments and size-fractionated biomass in the Chukchi and Beaufort Seas showed spatial and temporal variation during the spring and summer of 2002. Cluster analysis of pigment ratios revealed different assemblages over the shelf, slope and basin regions. In spring, phytoplankton with particle sizes greater than 5 μm, identified as diatoms and/or haptophytes, dominated over the shelf. Smaller (<5 μm) phytoplankton containing chlorophyll b, most likely prasinophytes, were more abundant over the slope and basin. Due to extensive ice cover at this time, phytoplankton experienced low irradiance, but nutrients were near maximal for the year. By summer, small prasinophytes and larger haptophytes and diatoms co-dominated in near-surface assemblages in largely ice-free waters when nitrate was mostly depleted. Deeper in the water column at 1–15% of the surface irradiance larger sized diatoms were still abundant in the upper nutricline. Phytoplankton from the shelf appeared to be advected through Barrow Canyon to the adjacent basin, explaining similar composition between the two areas in spring and summer. Off-shelf advection was much less pronounced for other slope and basin areas, which are influenced by the low-nutrient Beaufort gyre circulation, leading to a dominance of smaller prasinophytes and chlorophytes. The correlation of large-sized fucoxanthin containing phytoplankton with the higher primary production measurements shows promise for trophic status to be estimated using accessory pigment ratios.  相似文献