一种新的激光点云数据精简方法     

喜文飞  方源敏  李帅  李健 《测绘工程》2012,21(4):38-40

三维激光扫描技术是最近几年在测量方面发展起来的一个研究热点。提出利用点云模型中相邻三角形夹角的大小来对点云数据进行直接精简的方法,在matlab平台下,通过编程实现点云数据的压缩。将精简的点云数据通过编程重新构建三角网,最后在Geomagic软件中建模,通过与原始模型进行对比,新方法的压缩效果比较理想。  相似文献   

Optical attenuation in fog at a wavelength of 1.55 micrometers     

K.W. Fischer  M.R. Witiw  E. Eisenberg 《Atmospheric Research》2008,87(3-4):252

As part of a series of studies on laser propagation for terrestrial free space optical (FSO) telecommunications or laser telecommunications, an experiment was conducted to determine the relationship between visibility in fog and optical attenuation (dB/km) at a laser wavelength of 1.55 μm. In the telecommunications industry, a semi-empirical equation, called the Kruse formula [Kruse, P.W., McGlauchlin, L., McQuistan, R.B., 1962. Elements of infrared technology: generation, transmission, and detection. John Wiley and Sons, New York] is typically used to calculate expected attenuation for a given meteorological visibility. The Kruse formula, however, was developed to relate meteorological visibility to optical attenuation over wavelengths from the visible to the near infrared (IR), and for dust and small particle aerosols with dimensions much smaller than the wavelength. Typically, suspended small aerosols have diameters that average about 0.1 μm while fog droplets have diameters that range upward from 2.5 μm with mean diameters that exceed 10 μm in some fogs. Therefore, application of the Kruse formula to attenuation in fog is not appropriate since fogs consist mainly of particles much larger than the laser wavelength. As part of the experiment, a transmissometer with an 85-m baseline and a dynamic range of 60 dB operated for thirteen months in an area prone to radiation fog. A commercial visibility sensor, similar to those used at airports, was located near the middle of the optical path of the transmissometer and operated over the same period. The largest attenuation measured at this site was just over 300 dB/km, corresponding to a visibility of 32 m. The key finding of the study is that the generally accepted Kruse formula relating visibility and optical attenuation may be too pessimistic at low visibilities, and actual attenuation values for a given visibility may be more than 20% lower than previously thought. At visibilities exceeding about 650 m, the Kruse formula gives a good estimate of optical attenuation.  相似文献   

Geomorphic expression of neotectonic activity in a low relief area in an Airborne Laser Scanning DTM: A case study of the Little Hungarian Plain (Pannonian Basin)     

Balzs Szkely  Andrs Zmolyi  Erich Draganits  Christian Briese 《Tectonophysics》2009,474(1-2):353

The NW corner of the Little Hungarian Plain, which lies at the junction of the Eastern Alps, the Pannonian Basin and the Western Carpathians, is a neotectonically active region linking the extrusional tectonics of the Eastern Alps with the partly subsiding Little Hungarian Plain. The on-going deformation is verified by the earthquake activity in the region. An extremely flat part of the area, east of Neusiedlersee, the so-called Seewinkel, has been investigated with Airborne Laser Scanning (ALS, also known as airborne LiDAR) techniques, resulting in a digital terrain model (DTM) with a 1 m grid resolution and vertical precision of better than 10 cm. The DTM has been compared with known and inferred neotectonic features.Potential neotectonic structures of the DTM have been evaluated, together with geological maps, regional tectono-geomorphic studies, geophysical data, earthquake foci, as well as geomorphological features and the Quaternary sediment thickness values of the Seewinkel and the adjacent Parndorfer plateau. A combined evaluation of these data allows several tectonic features with a relief of < 2 m to be recognized in the DTM. The length of these linear geomorphological structures ranges from several hundred meters up to several kilometers. The most prominent feature forms a 15 km long, linear, 2 m high NE–SW trending ridge with gravel occurrences having an average grain size of ca. 5 cm on its top. We conclude this feature to represent the surface expression of the previously recognized Mönchhof Fault. In general, this multi-disciplinary case study shows that ALS DTMs are extremely important for tectono-geomorphic investigations, as they can detect and accurately locate neotectonic structures, especially in low-relief areas.  相似文献   

2013年芦山Ms7.0地震前重力场源变化分析     

王林海  陈石  张贝  卢红艳 《地震》2021,41(1):78-92

陆地重力观测获取的时变重力信号是研究地壳内部孕震区介质变化的重要依据。利用贝叶斯平差方法处理了川西地区2010—2012年的流动重力观测资料,发现相对重力仪的格值系数在两年内变化可达2×10^-4,而且仪器存在较小的非线性漂移率;重力场累积动态变化图像显示,2013年芦山MS7.0地震发生在重力梯度带零值线与龙门山断裂带交会部位附近。进一步采用等效源方法划定了测网内以雅安、康定和石棉为中心的场源分辨能力较高的区域,并反演了地震前的地壳视密度变化。场源视密度动态变化结果表明:2013年芦山MS7.0地震前2年,在龙门山断裂带的南侧和鲜水河断裂南段的东侧区域形成了范围较大的等效视密度增加区,而在小金至康定一带和都江堰周边地区也存在小规模的视密度增加。本文基于陆地时变重力测量结果反演得到芦山地震前的地壳内部等效视密度变化,可为研究壳内深部孕震环境变化特征提供参考。  相似文献   

气候变化对陆地水循环影响研究的问题   总被引：29，自引：5，他引：24  

刘春蓁 《地球科学进展》2004,19(1):115-119

简要地回顾了现存的由气候情景驱动水文模型研究气候变化对陆地水循环影响的方法。指出这种单向连接方法很难将气候变暖及人类活动引起的陆地水循环变化反馈给大气。这既影响对降雨的预测精度,又不能正确地描写陆地水循环的变化。近10年来气候学家对大气环流模型中陆面过程模型的改进以及水文气候学家对大尺度水文模型研究所取得的进展,展现了它们之间的互补性,以及未来用水文-气候耦合模型方法研究气候变化与人类活动对陆地水循环影响及水资源预测的可能性。  相似文献   

西藏拉琼锑金矿床流体包裹体特征及地质意义     

刘行  邹灏  李阳  蒋修未  李蝶 《地质论评》2019,65(Z1):223-224

正拉琼锑金矿床位于措美县西约17 km,大地构造位于青藏高原南部的特提斯喜马拉雅构造带东段,地处于印度河—雅鲁藏布江缝合带(IYZS)与藏南拆离系(STDS)大断裂之间。由于印度板块与欧亚板块碰撞之后,导致印度洋持续扩张,造成印度大陆不断向北挤压,形成喜马拉雅造山带(尹安,2000),该地区近东西向的断裂自北而南依次  相似文献   

南海IODP 349航次基底玄武岩中碳酸盐岩脉的岩石学特征*     

许佳锐  陈毅凤  王宝云 《热带海洋学报》2018,37(6):63-73

国际大洋发现计划(International Ocean Discovery Program, IODP)349航次在南海东部次海盆和西南次海盆残留扩张脊附近的U1431和U1433站位首次钻取基底玄武岩, 通过对16块基底玄武岩内的碳酸盐岩脉薄片镜下观察以及激光拉曼光谱分析, 揭示碳酸盐矿物为方解石和文石, 为典型的洋壳低温热液蚀变次生矿物。U1431站位碳酸盐岩脉为独立的方解石脉、文石脉交替出现; 而U1433站位则存在方解石脉、文石脉和方解石-文石共生脉三种情况。此外, U1431站位在基底~42.1m处出现了平行的方解石脉和文石脉, 揭示U1431存在不同来源热液的多期活动, 即可能存在多次或多阶段不同的热液注入。U1431和U1433站位的碳酸岩脉中, 文石的矿物集合体形状基本一致, 呈块状、纤维状和放射纤维状; 而方解石存在差异, U1431的方解石以斑块状、块状、粒状和纤维状出现, 而U1433的方解石仅出现块状。U1431站位的碳酸盐岩脉的丰度明显高于U1433站位。这些均揭示U1431站位的低温热液活动强, 而U1433站位则相对弱。两个站位的热液活动不同很可能是由于区域地质环境的差异造成——U1431附近的巨大海山为其提供了热液补给, 而U1433远离热液的补给/渗漏点。  相似文献   

机载WIDAS数据的Landsat卫星反照率初步验证   总被引：1，自引：1，他引：0  

何丹丹  焦子锑  董亚冬  张小宁  丁安心  尹思阳  崔磊  常雅轩 《遥感学报》2019,23(1):53-61

随着精细化监测的需求,中高空间分辨率的地表反照率产品逐渐成为气候模型的主要输入。目前,中高空间分辨率反照率产品的验证主要基于地表站点的通量塔观测数据,区域机载飞行数据的验证依然相对较少。因此,本文基于区域机载数据验证Landsat反照率产品。针对内蒙古自治区根河森林试验区所获取的机载红外广角双模式成像仪(WIDAS)多角度反射率数据,应用BRDF原型反演算法估算其反照率,分析了应用机载数据验证中高空间分辨率反照率产品的潜力。2016年内蒙古根河森林试验区机载WIDAS飞行多角度观测的可用多角度范围为25°,以前的研究表明BRDF原型反照率反演算法表现出对小观测角度的反照率反演结果的鲁棒性。因此,机载WIDAS反照率在一定程度可用于星载反照率的验证。首先,基于核驱动模型和各向异性平整指数(AFX)提取了试验区4种MODIS二向性反射分布函数(BRDF)原型;然后,将其作为先验知识应用到根河森林WIDAS机载数据的反照率反演中;最后,用WIDAS反照率和单个地面通量塔观测的反照率对Landsat卫星数据的反照率进行初步验证。验证结果表明Landsat反照率与WIDAS反照率结果较为一致,但略有低估,总体均方根误差(RMSE)约为0.02,偏差为0.0057。在多角度观测范围较小时,BRDF原型的反照率反演算法可为星载地表反照率的验证提供了一种有效的验证手段。  相似文献   

Inter-comparison of remote sensing platforms for height estimation of mango and avocado tree crowns     

《International Journal of Applied Earth Observation and Geoinformation》2020

To support the adoption of precision agricultural practices in horticultural tree crops, prior research has investigated the relationship between crop vigour (height, canopy density, health) as measured by remote sensing technologies, to fruit quality, yield and pruning requirements. However, few studies have compared the accuracy of different remote sensing technologies for the estimation of tree height. In this study, we evaluated the accuracy, flexibility, aerial coverage and limitations of five techniques to measure the height of two types of horticultural tree crops, mango and avocado trees. Canopy height estimates from Terrestrial Laser Scanning (TLS) were used as a reference dataset against height estimates from Airborne Laser Scanning (ALS) data, WorldView-3 (WV-3) stereo imagery, Unmanned Aerial Vehicle (UAV) based RGB and multi-spectral imagery, and field measurements. Overall, imagery obtained from the UAV platform were found to provide tree height measurement comparable to that from the TLS (R² = 0.89, RMSE = 0.19 m and rRMSE = 5.37 % for mango trees; R² = 0.81, RMSE = 0.42 m and rRMSE = 4.75 % for avocado trees), although coverage area is limited to 1–10 km² due to battery life and line-of-sight flight regulations. The ALS data also achieved reasonable accuracy for both mango and avocado trees (R² = 0.67, RMSE = 0.24 m and rRMSE = 7.39 % for mango trees; R² = 0.63, RMSE = 0.43 m and rRMSE = 5.04 % for avocado trees), providing both optimal point density and flight altitude, and therefore offers an effective platform for large areas (10 km²–100 km²). However, cost and availability of ALS data is a consideration. WV-3 stereo imagery produced the lowest accuracies for both tree crops (R² = 0.50, RMSE = 0.84 m and rRMSE = 32.64 % for mango trees; R² = 0.45, RMSE = 0.74 m and rRMSE = 8.51 % for avocado trees) when compared to other remote sensing platforms, but may still present a viable option due to cost and commercial availability when large area coverage is required. This research provides industries and growers with valuable information on how to select the most appropriate approach and the optimal parameters for each remote sensing platform to assess canopy height for mango and avocado trees.  相似文献   

Ground-based hyperspectral imaging and terrestrial laser scanning for fracture characterization in the Mississippian Boone Formation     

《International Journal of Applied Earth Observation and Geoinformation》2017

Petroleum geoscientists have been using cores and well logs to study source rocks and reservoirs, however, the inherent discontinuous nature of these data cannot account for horizontal heterogeneities. Modern exploitation requires better understanding of important source rocks and reservoirs at outcrop scale. Remote sensing of outcrops is becoming a first order tool for reservoir analog studies including horizontal heterogeneities. This work used ground-based hyperspectral imaging, terrestrial laser scanning (TLS), and high-resolution photography to study a roadcut of the Boone Formation at Bella Vista, northwest Arkansas, and developed an outcrop model for reservoir analog analyses.The petroliferous Boone Formation consists of fossiliferous limestones interbedded with chert of early Mississippian age. We used remote sensing techniques to identify rock types and to collect 3D geometrical data. Mixture tuned matched filtering classification of hyperspectral data show that the outcrop is mostly limestones with interbedded chert nodules. 1315 fractures were classified according to their strata-bounding relationships, among these, larger fractures are dominantly striking in ENE – WSW directions. Fracture extraction data show that chert holds more fractures than limestones, and both vertical and horizontal heterogeneities exist in chert nodule distribution.Utilizing ground-based remote sensing, we have assembled a virtual outcrop model to extract mineral composition as well as fracture data from the model. We inferred anisotropy in vertical fracture permeability based on the dominancy of fracture orientations, the preferential distribution of fractures and distribution of chert nodules. These data are beneficial in reservoir analogs to study rock mechanics and fluid flow, and to improve well performances.  相似文献