The method adopted here is based on the rigorous solution of Poison’s equation for logarithmic disturbance density within finite thickness galaxies. After their spiral arms are fitted directly with logarithmic spiral...The method adopted here is based on the rigorous solution of Poison’s equation for logarithmic disturbance density within finite thickness galaxies. After their spiral arms are fitted directly with logarithmic spirals, the morphological parameters, scale heights and their relative errors for 32 spiral galaxies, such as NGC4814, are ob-tained.展开更多
A sectional curve feature extraction algorithm based on multi-scale analysis is proposed for reverse engineering. The algorithm consists of two parts: feature segmentation and feature classification. In the first part...A sectional curve feature extraction algorithm based on multi-scale analysis is proposed for reverse engineering. The algorithm consists of two parts: feature segmentation and feature classification. In the first part,curvature scale space is applied to multi-scale analysis and original feature detection. To obtain the primary and secondary curve primitives,feature fusion is realized by multi-scale feature detection information transmission. In the second part: projection height function is presented based on the area of quadrilateral,which improved criterions of sectional curve feature classification. Results of synthetic curves and practical scanned sectional curves are given to illustrate the efficiency of the proposed algorithm on feature extraction. The consistence between feature extraction based on multi-scale curvature analysis and curve primitives is verified.展开更多
This paper presents an analysis of four open-source Global Digital Elevation Models (GDEMs) and compares them on two topographic profiles (nearly flat, and hills regions) for mapping and geomatics applications. The ch...This paper presents an analysis of four open-source Global Digital Elevation Models (GDEMs) and compares them on two topographic profiles (nearly flat, and hills regions) for mapping and geomatics applications. The chief intention is to investigate if GDEMs-based heights, contour intervals, slopes, and topographic profiles are valid for all map scales of topographic mapping, which constitutes a major issue in mapping activities. Two case studies, the Nile delta in Egypt and Makkah city in Saudi Arabia, have been utilized to represent flat and moderate-topography patterns. The investigated GDEMs include the most-recent released models: ASTER v.3, ACE 2, SRTMGL1 v.3, and NASADEM_HGT v.1 released in 2019 and 2020 with spatial resolutions of 1 and 3 arc seconds. Available accurate Ground Control Points (GCP) consist of 540 stations in the Nile delta and 175 stations in Makkah. Based on the available datasets in two study areas, it has been found that the accuracy of investigated GDEMs over known checkpoints ranges from ±2.5 and ±5.1 meters in the Nile delta region, while it varies between ±5.1 and ±8.0 meters in the Makkah area. That indicates that the utilization of GDEMs in topographic mapping differs significantly between flat and hilly spatial regions. Therefore, it is recommended to avoid using GDEMs for developing topographic maps of scale 1:25,000 or larger in flat regions and map scale 1:50,000 or larger in hilly regions. Additionally, the accomplished results showed that all GDEM-based slopes do not match with the actual slopes from known GCP over cross section’s length up to 30 kilometers. Thus, it is concluded that GDEMs are not the appropriate heights’ source for topographic mapping at medium and large map scales, and could not be utilized for topographic profiling in precise engineering and geomatics applications.展开更多
A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency wav...A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.展开更多
顶部电离层是指F2层电子密度最大值所在高度以上的电离层区域。掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究具有重要作用。标高是构建顶部以上电离层电子密度剖面模型的重要参数。本文使用...顶部电离层是指F2层电子密度最大值所在高度以上的电离层区域。掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究具有重要作用。标高是构建顶部以上电离层电子密度剖面模型的重要参数。本文使用2007—2020年的气象、电离层和气候星座观测系统(Constellation Observing System for Meteorology,Ionosphere and Climate,COSMIC)掩星观测数据,提取有效电子密度剖面数据的顶部标高,分析了其随地方时、季节、经纬度和太阳活动水平的变化特性。结果表明:顶部标高具有明显的日变化和季节变化规律,并且表现出强烈的太阳活动依赖性;顶部标高在纬度上的变化强烈依赖于地方时,同时在东西经向上表现出明显的波状结构,且这种经度波状结构在南北半球具有不同的形态;顶部标高在夏季半球具有显著的东西经向差异,南半球夏季更为明显。展开更多
水汽标高是一个反映水汽垂直分布特征的参数,也是全球导航卫星系统(global navigation satellite system,GNSS)对流层天顶湿延迟改正和GNSS水汽层析中的一个辅助参数。本文对2006—2012年水汽标高的时间序列进行频谱分析,发现水汽标高...水汽标高是一个反映水汽垂直分布特征的参数,也是全球导航卫星系统(global navigation satellite system,GNSS)对流层天顶湿延迟改正和GNSS水汽层析中的一个辅助参数。本文对2006—2012年水汽标高的时间序列进行频谱分析,发现水汽标高在时间上呈现出年周期和半年周期变化,因此利用包含年周期和半年周期的三角函数来表达水汽的时变规律,然后利用欧洲中尺度天气预报中心(European Centre for Medium-range Weather Forecasting,ECMWF)的数据在全球1°×1°的格网点上分别拟合了三角函数的系数。通过上述方法首次构建了一个全球适用的水汽标高模型GSH,该模型既体现了水汽标高的时变特性又考虑了其地理差异。以无线电探空数据为参考,GSH具有-0.19km的偏差(bias)和1.81km的均方根误差(root mean square error,RMSE);以ECMWF数据为参考,GSH具有0.04km的bias和1.52km的RMSE。GSH整体上表现出了比较稳定的精度,可服务于GNSS气象学研究,也可为其他相关气象研究提供水汽标高参考。展开更多
文摘The method adopted here is based on the rigorous solution of Poison’s equation for logarithmic disturbance density within finite thickness galaxies. After their spiral arms are fitted directly with logarithmic spirals, the morphological parameters, scale heights and their relative errors for 32 spiral galaxies, such as NGC4814, are ob-tained.
基金Supported by the Natural Science Foundation of China (50175063)
文摘A sectional curve feature extraction algorithm based on multi-scale analysis is proposed for reverse engineering. The algorithm consists of two parts: feature segmentation and feature classification. In the first part,curvature scale space is applied to multi-scale analysis and original feature detection. To obtain the primary and secondary curve primitives,feature fusion is realized by multi-scale feature detection information transmission. In the second part: projection height function is presented based on the area of quadrilateral,which improved criterions of sectional curve feature classification. Results of synthetic curves and practical scanned sectional curves are given to illustrate the efficiency of the proposed algorithm on feature extraction. The consistence between feature extraction based on multi-scale curvature analysis and curve primitives is verified.
文摘This paper presents an analysis of four open-source Global Digital Elevation Models (GDEMs) and compares them on two topographic profiles (nearly flat, and hills regions) for mapping and geomatics applications. The chief intention is to investigate if GDEMs-based heights, contour intervals, slopes, and topographic profiles are valid for all map scales of topographic mapping, which constitutes a major issue in mapping activities. Two case studies, the Nile delta in Egypt and Makkah city in Saudi Arabia, have been utilized to represent flat and moderate-topography patterns. The investigated GDEMs include the most-recent released models: ASTER v.3, ACE 2, SRTMGL1 v.3, and NASADEM_HGT v.1 released in 2019 and 2020 with spatial resolutions of 1 and 3 arc seconds. Available accurate Ground Control Points (GCP) consist of 540 stations in the Nile delta and 175 stations in Makkah. Based on the available datasets in two study areas, it has been found that the accuracy of investigated GDEMs over known checkpoints ranges from ±2.5 and ±5.1 meters in the Nile delta region, while it varies between ±5.1 and ±8.0 meters in the Makkah area. That indicates that the utilization of GDEMs in topographic mapping differs significantly between flat and hilly spatial regions. Therefore, it is recommended to avoid using GDEMs for developing topographic maps of scale 1:25,000 or larger in flat regions and map scale 1:50,000 or larger in hilly regions. Additionally, the accomplished results showed that all GDEM-based slopes do not match with the actual slopes from known GCP over cross section’s length up to 30 kilometers. Thus, it is concluded that GDEMs are not the appropriate heights’ source for topographic mapping at medium and large map scales, and could not be utilized for topographic profiling in precise engineering and geomatics applications.
文摘A barotropic model containing large-scale topography and zonal mean flow is established to discuss the effects of large-scale topography on the low-frequency waves. The results show that what affects low-frequency waves mostly is maximal height of topography and topographic slope. The former makes frequency of topographic Rossby waves decrease, the latter makes Rossby waves instable. Moreover, when topographic slope is appropriate, it can also make Rossby waves turn into low-frequency waves.
文摘顶部电离层是指F2层电子密度最大值所在高度以上的电离层区域。掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究具有重要作用。标高是构建顶部以上电离层电子密度剖面模型的重要参数。本文使用2007—2020年的气象、电离层和气候星座观测系统(Constellation Observing System for Meteorology,Ionosphere and Climate,COSMIC)掩星观测数据,提取有效电子密度剖面数据的顶部标高,分析了其随地方时、季节、经纬度和太阳活动水平的变化特性。结果表明:顶部标高具有明显的日变化和季节变化规律,并且表现出强烈的太阳活动依赖性;顶部标高在纬度上的变化强烈依赖于地方时,同时在东西经向上表现出明显的波状结构,且这种经度波状结构在南北半球具有不同的形态;顶部标高在夏季半球具有显著的东西经向差异,南半球夏季更为明显。
文摘水汽标高是一个反映水汽垂直分布特征的参数,也是全球导航卫星系统(global navigation satellite system,GNSS)对流层天顶湿延迟改正和GNSS水汽层析中的一个辅助参数。本文对2006—2012年水汽标高的时间序列进行频谱分析,发现水汽标高在时间上呈现出年周期和半年周期变化,因此利用包含年周期和半年周期的三角函数来表达水汽的时变规律,然后利用欧洲中尺度天气预报中心(European Centre for Medium-range Weather Forecasting,ECMWF)的数据在全球1°×1°的格网点上分别拟合了三角函数的系数。通过上述方法首次构建了一个全球适用的水汽标高模型GSH,该模型既体现了水汽标高的时变特性又考虑了其地理差异。以无线电探空数据为参考,GSH具有-0.19km的偏差(bias)和1.81km的均方根误差(root mean square error,RMSE);以ECMWF数据为参考,GSH具有0.04km的bias和1.52km的RMSE。GSH整体上表现出了比较稳定的精度,可服务于GNSS气象学研究,也可为其他相关气象研究提供水汽标高参考。
