Vertical accuracy evaluation of freely available latest high-resolution (30 m) global digital elevation models over Cameroon (Central Africa) with GPS/leveling ground control points.     

Loudi Yap  Ludovic Houetchak Kandé  Robert Nouayou  Nasser Abdou Ngouh  Marie Brigitte Makuate 《International Journal of Digital Earth》2019,12(5):500-524

Digital Elevation Models (DEMs) contain topographic relief data that are vital for many geoscience applications. This study relies on the vertical accuracy of publicly available latest high-resolution (30?m) global DEMs over Cameroon. These models are (1) the ALOS World 3D-30?m (AW3D30), (2) the Shuttle Radar Topography Mission 1 Arc-Second C-Band Global DEM (SRTM 1) and (3) the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2 (ASTER GDEM 2). After matching their coordinate systems and datums, the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs. After this, the three models are compared among them, in order to access random and systematic effects in the elevation data each of them contains. Further, heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM, for their vertical accuracy determination. Traditional and robust statistical measures, normality test, outlier detection and removal were used to describe the vertical quality of the DEMs. The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs. Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square (RMS) and Normalized Median Absolute Deviation (NMAD) are: AW3D30 (13.06?m and 7.75?m), SRTM 1 (13.25?m and 7.41?m) and ASTER GDEM 2 (18.87?m and 13.30?m). Other accuracy measures (MED, 68.3% quantile, 95% quantile) supply some evidence of the good quality of AW3D30 over Cameroon. Further, the effect of land cover and slope on DEM vertical accuracy was also analyzed. All models have proved to be worse in the areas dominated by forests and shrubs areas. SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas. The dependency of DEMs accuracy on the terrain roughness is evident. In all slope intervals, AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon. AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.  相似文献   

Integrated methodology for determining provenance of detrital quartz using optical petrographic microscopy and cathodoluminescence (CL) properties     

《Marine and Petroleum Geology》2017

The provenance of detrital quartz is a useful predictor in frontier basin sandstone reservoirs of the availability of coarse-grained quartz grains of plutonic or high grade metamorphic origin. The standard approach is to use scanning electron microscope (SEM) panchromatic cathodoluminescence (CL) imagery and observations from an optical petrographic microscope. We describe a work flow, modified from previous literature proposals, to determine quartz provenance in detrital grains using optical petrographic microscopy and CL properties from both a hot-cathode cathodoluminescence microscope attachment (HCMA) and panchromatic SEM-CL. HCMA analysis permits better discrimination of different types of metamorphic quartz. This method is applied to a Middle Jurassic to Lower Cretaceous section in the Bandol-1 wildcat well, located in the Laurentian sub-basin south of Newfoundland. Two types of high-grade metamorphic quartz are distinguished, one with low luminescence as described in previous literature and one with medium blue CL colour and a moderate colour shift that is also known from granulite in the hinterland. Three phases of detrital supply are identified, suggesting progressive unroofing of higher grade metamorphic sources through the middle Jurassic and major input of plutonic quartz in the early Cretaceous.  相似文献   

基于数据挖掘的GF-1 遥感影像绿潮自适应阈值分区智能检测方法研究   总被引：1，自引：0，他引：1  

王蕊  王常颖  李劲华 《海洋学报》2019,41(4):131-144

由于受到云雾的影响，可见光影像能够高效用于绿潮检测的数据源较为有限，特别是云覆盖较为严重的可见光影像，基本无法用于检测绿潮。即使影像数据是在薄云、薄雾、无云覆盖的情况下获取的，由于其光谱反射值存在较大差异，依然很难采用同一阈值进行绿潮检测。基于此，为了提高可见光影像的利用率，实现不同云覆盖情况下，绿潮的高精度自适应阈值的自动检测，本文以GF-1影像为数据源，首先采用K-means聚类和C4.5决策树方法实现影像云覆盖情况的自动识别；其次，选取大量不同云覆盖情况下子图像样本（每个子图像样本中均包含绿潮和海水两类），分析得出不同云覆盖情况下绿潮和海水的区分阈值y与影像光谱差x=band_nir-band_red之间所具有的线性关系；然后，利用分析得出的线性关系提出一种适用于GF-1影像的绿潮分区自适应阈值自动检测方法。最后，为验证提出方法的有效性，分别采用NDVI方法、EVI方法和本文提出的自适应阈值自动检测方法进行绿潮提取实验。实验结果表明，对于GF-1卫星遥感数据，本文提出的绿潮自适应阈值分区自动检测方法明显优于传统的NDVI和EVI检测方法，不仅提高了绿潮的监测精度，而且实现了绿潮提取的全自动化。  相似文献   

珞珈一号01星夜光遥感设计与处理   总被引：2，自引：0，他引：2  

李德仁  张过  沈欣  钟兴  蒋永华  汪韬阳  涂建光  李治江 《遥感学报》2019,23(6):1011-1022

珞珈一号01星是兼具遥感和导航的一星多用低轨维纳科学试验卫星,本文针对珞珈一号01星夜光遥感设计与处理,详细介绍了卫星平台的有效载荷及平台设计;面向科学的试验目标,制订了科学的夜光成像任务计划,实现了全国夜光一张图任务规划;提出了面向珞珈一号01星的在轨几何辐射定标模型;研制了支持WEB端及移动端访问的数据共享服务系统;针对夜光遥感数据在社会经济应用问题,提出了发展指数和未来发展指数的珞珈一号指数模型,并通过相关实验验证了模型的有效性。珞珈一号01星可为社会经济参数估算、重大事件评估、渔业监测、国家安全等领域提供技术支撑。  相似文献   

基于SAR干涉数据的东帕米尔高原冰川变化     

郭唯娜  柯长青  范宇宾 《地球信息科学学报》2019,21(11):1790-1801

冰川变化监测对生态灾害预防、区域水资源调控、气候变化研究等意义重大。利用冰川在雷达干涉影像上表现出失相干这一特性,选用1998年ERS 1/2与2018年 Sentinel-1A重轨单视复数SAR数据,通过相干系数取阈值的方法获取东帕米尔高原两个时期的冰川边界,以Landsat TM/OLI影像和全球陆地冰川空间监测计划发布的数据验证本文冰川边界提取的精度,从而分析冰川变化。结果表明：① 拟合研究区相干系数图上相干系数γ与对应像元个数的曲线关系,冰川区像元个数会在低相干区域积累形成一个小的波峰。曲线一阶导数变缓的点（冰川区向非冰川区过渡的转折点）即为所选阈值点,利用SAR相干系数取阈值法提取的冰川边界与光学遥感影像结合RGI6.0数据提取的验证冰川边界具有较好的一致性,SAR干涉相干系数提取冰川边界的方法是可行而有效的,ERS 1/2与Sentinel-1A提取的冰川总面积精度均在90%以上,而且SAR数据能够有效提取光学遥感影像难以识别的冰川表碛覆盖;② 1998年和2018年东帕米尔高原冰川总面积减少了318.59 km2,年平均变化速率为-15.93 km2/a,冰川退缩面积占冰川总面积的23%;③ 对大、中型规模冰川来说,表碛覆盖型冰川退缩较其他冰川明显;从坡向上来看,20年各个坡向冰川均有所退缩,其中东南坡冰川退缩最多,西坡冰川退缩最少;从海拔上来看,1998年冰川集中分布在4519~5421 m海拔区间内,2018年集中分布在4682~5320 m海拔区间内;在3325~5710 m海拔区间内冰川退缩明显,4915 m海拔附近达到退缩极大值。  相似文献   

以内陆水体为观测目标的GF-1影像常规融合方法评价   总被引：1，自引：0，他引：1  

杜泳  张霄宇  毛志华  陈建裕 《海洋学报(英文版)》2019,38(1):172-179

内陆水体的研究需要遥感影像具备高空间分辨率和高光谱分辨率，这使得影像的全色（PAN）波段和多光谱（MS）波段之间的融合尤为重要。本文以钱塘江大缺口段为研究对象，采用四种常规融合方法，包括Pan Sharpening（PS）、主成分分析（PCA）、Gram Schmidt（GS）和小波分析（WF），分别对GF-1影像开展了全色波段和多光谱波段的融合方法评价。研究结果表明，GS融合后的影像效果最好，随后分别是PCA、WF和PS。由于水陆之间反射率信息获取的根本差异，大面积水体的存在会影响到融合影像保留源图像空间和光谱信息的能力。因而，在进行遥感影像融合时，融合方法的选择需要考虑影像中水域面积的分布情况。  相似文献   

Remote sensing mapping of macroalgal farms by modifying thresholds in the classification tree     

Yuhan Zheng  Carlos M. Duarte  Jiang Chen  Dan Li  Zhaohan Lou 《国际地球制图》2019,34(10):1098-1108

Remote sensing is the main approach to map aquatic vegetation, and classification tree (CT) is superior to various classification methods. Based on previous studies, modified CT can be developed from traditional CT by adjusting the thresholds based on the statistical relationship between spectral features to classify different images without ground-truth data. However, no studies have yet employed this method to resolve marine vegetation. In this study, three Gao-Fen 1 satellite images obtained on 30 January 2014, 5 November 2014 and 21 January 2015 were selected, and two features were then employed to extract macroalgae farms. Results show that the overall accuracies of traditional CTs for three images are 92.0, 94.2 and 93.9%, respectively, whereas those of the two corresponding modified CTs for images obtained on 21 January 2015 and 5 November 2014 are 93.1 and 89.5%, respectively. This indicates modified CTs can map macroalgae with multi-date imagery and monitor their spatiotemporal distribution in coastal environments.  相似文献   

国产高分卫星遥感影像融合方法比较与评价     

邵亚奎  朱长明  张新  沈谦 《测绘通报》2019,(6):5-10

选择适宜的融合方法有利于卫星遥感影像融合产品更好地服务于生产实践及科学研究。本文在总结现有影像像素级融合算法原理的基础上，选用Pansharp、Gram-Schmidt、HPF、Ehlers、Subtractive、Modified IHS、Brovey、PCA、NNDiffuse等多种常用的影像融合方法对国产高分影像的全色和多光谱数据进行了融合处理，并从定性和定量的角度对融合结果进行了详细评价，试图寻找适用于国产高分卫星遥感影像的最佳融合方法。结果表明：针对国产高分一号卫星遥感数据，超分辨率贝叶斯算法融合效果在视觉效果与影像质量定量评价指标中综合表现最佳；Gram-Schmidt、NNDiffuse、Subtractive和HPF融合结果地物边界最为清晰；Modified IHS、PCA、Brovey融合影像色彩失真较为明显；NNDiffuse在可见光波段表现较突出；Gram-Schmidt在近红外波段表现效果最佳。  相似文献   

Search for radio pulsations in four anomalous X-ray pulsars and discovery of two new pulsars     

Marta Burgay  Nanda Rea  GianLuca Israel  Andrea Possenti  Luciano Burderi  Tiziana Di Salvo  Nichi D’Amico  Luigi Stella  Elisa Nichelli 《Astrophysics and Space Science》2007,308(1-4):531-534

We have performed deep searches for radio pulsations from four southern anomalous X-ray pulsars (AXPs) to investigate their physical nature in comparison with the rotation powered pulsars. The data were acquired using the Parkes radio telescope with the 1.4 GHz multibeam receiver. No pulsed emission with periodicity matching the X-ray ephemeris have been found in the observed targets down to a limit of ∼0.1 mJy. A blind search has also been performed on all the 13 beams of the multibeam receiver (the central beam being pointed on the target AXP), leading to the serendipitous discovery of two new radio pulsars and to the further detection of 18 pulsars. Also a search for single dispersed pulses has been performed in the aim to detect signals similar to those of the recently discovered rotating radio transients.   相似文献   

HESS observations of extragalactic objects     

Matthias Beilicke 《Astrophysics and Space Science》2007,309(1-4):139-145

The HESS experiment (High Energy Stereoscopic System), consisting of four imaging atmospheric Cherenkov telescopes (IACTs) in Namibia, has observed many extragalactic objects in the search for very high energy (VHE) γ-ray emission. These objects include active galactic nuclei (AGN), notably Blazars, Seyferts, radio galaxies, starburst galaxies and others. Beyond the established sources, γ-ray emission has been detected for the first time from several of these objects by HESS, and their energy spectra and variability characteristics have been measured. Multi-wavelength campaigns, including X-ray satellites, radio telescopes, and optical observations, have been carried out for AGNs, in particular for PKS 2155-304, H 2356-309 and 1ES 1101-232, for which the implications concerning emission models are presented. Also results from the investigations of VHE flux variability from the giant radio galaxy M 87 are shown. For the HESS Collaboration.  相似文献