Delineation and geometric modeling of road networks     

Charalambos Poullis  Suya You 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(2):165-181

In this work we present a novel vision-based system for automatic detection and extraction of complex road networks from various sensor resources such as aerial photographs, satellite images, and LiDAR. Uniquely, the proposed system is an integrated solution that merges the power of perceptual grouping theory (Gabor filtering, tensor voting) and optimized segmentation techniques (global optimization using graph-cuts) into a unified framework to address the challenging problems of geospatial feature detection and classification.Firstly, the local precision of the Gabor filters is combined with the global context of the tensor voting to produce accurate classification of the geospatial features. In addition, the tensorial representation used for the encoding of the data eliminates the need for any thresholds, therefore removing any data dependencies.Secondly, a novel orientation-based segmentation is presented which incorporates the classification of the perceptual grouping, and results in segmentations with better defined boundaries and continuous linear segments.Finally, a set of gaussian-based filters are applied to automatically extract centerline information (magnitude, width and orientation). This information is then used for creating road segments and transforming them to their polygonal representations.  相似文献   

Modeling and querying approximate direction relations     

Shihong Du  Luo Guo 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):328-340

Existing models of direction relations are mainly designed to handle crisp regions. To accommodate uncertain spatial data, it is necessary to investigate the formalization, uncertain semantics, and composition operators for uncertain direction relations. In this study, direction relations about uncertain regions, i.e., approximate direction relations, are modeled as the combinations of four crisp direction relations. The approximate relations can be interpreted from two aspects: the lower part (only including crisp relations about uncertain region) and the uncertain part (the uncertain directions about uncertain regions). The uncertain semantics of uncertain directions are formalized, such as possibly north, possibly south, possibly southeast, etc. Both crisp and uncertain parts are used to simplify and handle the composition and the query of uncertain direction relations. Approximate direction relations are helpful to model directions concerned with both crisp and uncertain regions; they therefore can play important roles in handling uncertain data (in our case, querying uncertain data).  相似文献   

Milky-Way-Like 2175 Å Dust Extinction Feature Observed toward the Quasar SDSS J0916+2921     

《Chinese Astronomy and Astrophysics》2020,44(2):196-209

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基于SIC的伪卫星系统抗远近效应捕获算法研究          下载免费PDF全文

刘旭  姚铮  吕红丽  陆明泉 《全球定位系统》2020,45(1):12-18

地基伪卫星系统中由于远近效应的影响,近场伪卫星信号可能对远场伪卫星信号形成压制干扰,导致远场伪卫星信号无法被捕获. 针对该系统中使用的跳时直接序列扩频(TH-DSSS)信号的捕获问题,引入串行干扰消除(SIC)技术,缓解伪卫星系统中的远近效应问题,通过本地重构强信号和干扰对消降低强信号对弱信号捕获的影响,并从理论和仿真两方面对其性能进行了分析. 仿真结果表明,相比传统未采用干扰消除的捕获算法而言,基于SIC的信号捕获方法在不改变伪卫星基站结构和接收机框架的基础上,可有效降低远近效应的影响,提高弱信号捕获概率,扩大系统工作范围,从而为接收机在强远近效应场景下的捕获、跟踪和定位解算提供有效保障.   相似文献   

Automatic Solar Seeing Observations at Mt. Wumingshan in Western China     

T. F. Song  Y. M. Wen  Y. Liu  A. Elmhamdi  A. S. Kordi  M. Y. Zhao  X. F. Zhang  X. B. Li  J. X. Wang  Y. Fu  X. M. Cheng  F. Y. Xu 《Solar physics》2018,293(2):37

Mountain Wumingshan (Mt. WMS) is located in the southeastern foot of the Tibet Plateau with an altitude of 4,800 m. It is one of the candidate sites to place China’s next-generation large-scale solar telescope. A temporary observation platform has been built at Mt. WMS, but there is still a great need of a stable solar-seeing monitoring for long-term observations. Based on the preliminary studies on the Solar Differential Image Motion Monitor (SDIMM) of the Yunnan Observatories, we built an improved version of this early prototype, which is called Wumingshan Mountain Automated Solar Differential Image Motion Monitor (WMA-SDIMM). We develop the automatic system of the WMA-SDIMM, investigate the reliability and precision of our measurements by error analysis and comparison testing, and present the statistical results from October 2016 to September 2017 at Mt. WMS. WMA-SDIMM works very well at Mt. WMS and is quite suitable for long-period daytime seeing observations.  相似文献   

Removal of topographic effects from lunar images using Kaguya (LALT) and Earth-based observations     

Viktor V. Korokhin  Yuriy I. Velikodsky  Yuriy G. Shkuratov  Vadym G. Kaydash  Sergey Y. Gerasimenko  Nikolai V. Opanasenko  Gorden Videen  Carle Pieters 《Planetary and Space Science》2010,58(10):1298-1306

Lunar images acquired at non-zero phase angles show brightness variations caused by both albedo heterogeneities and local topographic slopes of the surface. To distinguish between these two factors, altimetry measurements or photoclinometry data can be used. The distinction is especially important for imagery of phase-function parameters of the Moon. The imagery is a new tool that can be used to study structural anomalies of the lunar surface. To illustrate the removal of the topographic effects from photometric images, we used Earth-based telescopic observations, altimetry measurements carried out with the Kaguya (JAXA) LALT instrument, and a new photoclinometry technique that includes analysis of several images of the same scenes acquired at different phase angles. Using this technique we have mapped the longitudinal component of lunar topography slopes (the component measured along the lines of constant latitude). We have found good correlations when comparing our map with the corresponding data from Kaguya altimetry. The removal of the topographic surface properties allows for the study of the phase-function parameters of the lunar surface, not only for flat mare regions, but for highlands as well.  相似文献   

Current spectra under varying stratification conditions in the central North Sea     

《Journal of Sea Research》2004,51(2):77-91

Given strongly different vertical stratification and not significantly different kinetic energy, ‘internal wave’ band spectral properties were studied using two 8-day representative sets of observations from the central North Sea in winter and summer. The observed similar spectral shape of the internal wave band was due to a combination of deterministic narrow band and intermittent signals. In addition to dominant tidal harmonics, 25% of total kinetic energy was found at inertial and non-linear inertial-tidal interaction frequencies in summer and about the same amount was found in broad-band response to atmospheric forcing in winter. The energy at the (seasonal) non-linear interaction frequencies was proportional to stratification, specifically, to near-inertial shear magnitude. In summer, motions at frequencies (σ) between f<σ<2.5 cpd (cycles per day) appeared in low vertical mode, whilst the power P(σ) of motions at σ>4±1 cpd obeyed canonical internal wave scaling P(σ)∼Cσ⁻², provided the shear magnitude ∣S∣ was used instead of the buoyancy frequency N for the factor C. Motions at 2.5<σ<4±1 cpd appeared as transition between the two regimes. In winter no inertial motions were observed.  相似文献   

Helium White Dwarf-main Sequence Star Mergerand Formation of Pulsating Hot Subdwarf Stars     

《Chinese Astronomy and Astrophysics》2020,44(3):325-333

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The effort factor: Evaluating the increasing marginal impact of resource extraction over time     

《Global Environmental Change》2014

Concern for the increasing impact of human activities on Earth's ecosystems has generated a growing effort to monitor those impacts and measure the success, if any, of mitigation measures. This contribution argues that ecological impact assessments that tend to rely primarily on the volume of natural resources produced and subsequently consumed overlook the degree to which ecological impact can vary significantly independently of production volumes, due to the varying impact that results from production effort. Production effort, in turn, is directly linked to the quality of raw materials, which inevitably tends to decrease over time. As a result, unless technological improvements were able to compensate for the resource quality decline indefinitely, we face a future of increasing marginal ecological impact over time. This is demonstrated here based on three resource extraction systems, coal mining in the UK, grain production in China, and global marine fisheries.  相似文献   

气象台站网布局优化研究综述     

程勇  杨玲  行鸿彦  王伟  王峰  周勇 《南京气象学院学报》2011,(6):511-518

气象台站网的布局优化可以提高气象台站观测资料的代表性、准确性和可比较性.简述了气象台站网布局优化方法的国内外研究进展,讨论了气象台站网布局优化方法的关键技术和存在的问题,重点介绍和分析了利用线性内插法、最优内插法、信息论法、因子分析法和经验模式法来进行气象台站网的布局优化,总结了这些方法的可行性.结合气象业务需求变化,提出了气象台站网布局优化方法的改进方向.  相似文献